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<h1>The Wonderful World of Linux 2.6</h1>
<p id="by"><b>By <A HREF="../authors/pranevich.html">Joe Pranevich</A></b></p>

<p>
<P ALIGN="center"><EM>[Reprinted from
<A HREF="http://kniggit.net/wwol26.htm">http://kniggit.net/wwol26.htm</A>
with the kind permission of the author.]</EM></P>

<p>Although it seems like only yesterday
that we were booting up our
first Linux 2.4 systems, time has ticked by and the kernel development
team has just released the 2.6 kernel to the public. This document is
intended as a general overview of the features in the new kernel
release, with a heavy bias toward i386 Linux. Please also be aware that
some of the "new"
features discussed here may have been back-ported to Linux 2.4 after
first appearing in Linux 2.6, either officially or by a distribution
vendor. I have also included information on a handful of cases where a
new feature originated during the maintenance cycle of Linux 2.4, and
those will be marked as appropriate in the text.
</p>
<p>At present, this document has been
translated into ten languages.
Please see the "<A HREF="">Translations</A>" section at the very bottom for more
information.
</p>


<h3>The Story So Far...</h3>
<p>The Linux kernel project was started in
1991 by Linus Torvalds as a
Minix-like Operating System for his 386. (Linus had originally wanted
to name the project Freax, but the now-familiar name is the one that
stuck.) The first official release of Linux 1.0 was in
March 1994, but it supported only single-processor i386 machines. Just
a year later, Linux 1.2 was released (March 1995) and was the first
version with support for
different hardware platforms (specifically: Alpha, Sparc, and Mips),
but still only single-processor models. Linux
2.0 arrived in June of 1996 and also included support for a number of
new
architectures, but more importantly brought Linux into the world of
multi-processor machines (SMP). After 2.0, subsequent major releases
have been somewhat slower in coming (Linux 2.2 in January 1999 and 2.4
in January 2001), each revision expanding Linux's support for new
hardware and system types as well as boosting scalability. (Linux 2.4
was also notable in being the release that really broke Linux into the
desktop space with kernel support for ISA Plug-and-Play, USB, PC Card
support, and other additions.) Linux 2.6, released 12/17/03,&nbsp;
stands not only to build
on these features, but also to be another "major leap" with improved
support for both significantly larger systems and significantly smaller
ones (PDAs and other devices.)</p>
<h2>Core Hardware Support </h2>
<p>One of the most important strengths of
Linux-powered operating
systems is their flexibility and their ability to support a wide range
of hardware platforms. While this document is geared specifically to
the uses of Linux on PC-derived hardware types, the Linux 2.6 kernel
has made some remarkable improvements in this area that deserve to be
pointed out.
</p>
<h3>Scaling Down -- Linux for Embedded Systems</h3>
One of the two most fundamental
changes to Linux in 2.6 comes through
the acceptance and merging of much of the uClinux project into the
mainstream kernel. The uClinux project (possibly
pronounced "you-see-Linux", but more properly spelled with the Greek
character "mu") is the Linux for Microcontrollers project. This variant
of Linux has already been a major driver of support for Linux in the
embedded market, and its inclusion in the official release should
encourage further development in this space. Unlike the "normal" Linux
ports that we are generally accustomed to, embedded ports do not have
all the features that we associate with the kernel, due to hardware
limitations. The primary difference is that these ports feature
processors that do not feature an MMU. ("memory management unit" - what
makes a protected-mode OS "protected") While these are generally true
multitasking
Linux systems, they are missing memory
protection and other related features. (Without memory protection, it
is possible for a wayward process to read the data of, or even crash,
other processes on the system.) This may make them unusable for a
multi-user system, but an excellent choice for a low-cost PDA or
dedicated device. It is difficult to over-emphasize this architecture
shift in Linux 2.6; all versions of Linux up to this point were derived
(however indirectly) from the
limitations inherent with Linus' initial work on his Intel 80386.

<p>There are several new lines of embedded
processors supported by
Linux 2.6, including Hitachi's H8/300 series, the NEC v850 processor,
and Motorola's line of
embedded m68k processors. Motorola's offerings are the most familiar to
the average Linux user as they are the
guts underneath Palm Pilots starting with the first (the Palm 1000), up
until the Palm III. Other models go by names such as
Dragonball and ColdFire and are included on systems and evaluation
boards manufactured by Motorola, Lineo, Arcturus, and others. Sadly,
support for other, older m68k processors without
MMUs (such as the 68000s used in early Macintoshes) is not yet covered
by the new release but it is highly possible that "hobbyist" projects
of the future will seek to support Linux on these and other antique
system.</p>

<p>Although not a part of the uClinux
merge, the new revision of Linux
also include support for
Axis
Communications' ETRAX CRIS ("Code Reduced Instruction Set") processors.
(Actual support
for this processor arrived as a feature during the 2.4 kernel's
maintenance cycle -- well after the 2.4.0 release-- so it deserves a
brief mention.) These are embedded
processor, but with MMUs, that is primarily used in network hardware.
Related
support for MMU-less variants of these processors has not yet been
accepted into the kernel, but are being worked on by outside projects.
</p>

<p>In addition to pure hardware support,
there have been a number of
other wins through the integration of the embedded work into the
mainline kernel. While most of these changes are under the hood,
changes such as ability to build a system completely without swap
support add to the overall robustness of the OS.</p>
<h3>Scaling Up -- NUMA and Bigger Iron</h3>
<p>The second of the two most fundamental
changes in Linux 2.6 happens
to work
in the other direction: to make Linux a more acceptable kernel on
larger and larger servers. (Some of these larger servers will be i386
based, and some not.) The big change in this respect is Linux's new
support
for NUMA servers. NUMA (or "Non-Uniform Memory Access") is a step
beyond SMP in the multi-processing world and is a major leap forward
for
efficiency on systems that have many processors. Current
multiprocessing systems were
designed with many of the same limitations as their uniprocessor
counterparts, especially as only a single pool of memory is expected to
serve all processors. On
a many-processor system,
there is a major performance bottleneck due to the extremely high
contention rate between the multiple cpus onto the single memory bus.
NUMA servers get around that difficulty by introducing the concept
that, for a specific processor, some memory is closer than others. One
easy way (and not terribly technically incorrect) to imagine this is
that you have a system built with separate cards, each containing CPUs,
memory,
and possibly other components (I/O, etc.) There are many of these cards
in a system and while they can all talk to each other, it's pretty
clear that the CPUs will have the easiest time talking to the local
memory (the memory on the cpu card rather than on a separate card.)You
can imagine the new NUMA architecture being somewhat similar to a very
tight-knit
cluster at the lowest levels of hardware.</p>

<p>To properly support these new NUMA
machines, Linux had to adapt in
several respects to make the new model efficient. To start with, an
internal topology API was created to actually let the kernel internals
understand one processor or one memory pool's relations to I/O devices
and each other. Derived from that, the Linux process scheduler now is
capable of understanding these relationships and will attempt to
optimize tasks for best use of local resources. Additionally, many NUMA
machines are built in such a way that they have "holes" in the linear
memory space "between" nodes. The new kernel is able to deal with those
discontiguous cases in a reasonable way. There are many other internal
changes which were made to allow Linux to support these new high-end
machines, and this is definitely an area of growth for the kernel as a
whole. However, this is an area where Linux is very rapidly growing
and maturing and much work remains to be done to make the most
efficient use of resources possible. Over the course of the next year,
we can expect to see many more
improvements in Linux's support for these very
high-end systems.
</p>
<h3>Subarchitecture Support</h3>
<p>While not quite as core as the two
previous changes, the new
revision of the kernel also includes a new concept
called a "subarchitecture" which further extends Linux's reach into new
hardware types. Previously, Linux often had the underlying
assumption that processor types and hardware types went hand in hand.
That is, that i386-descendant processors are only used on
PC/AT-descendant servers. In Linux 2.4, this assumption was broken for
i386 with the addition of support for SGI's Visual Workstation, a
"legacy-less" platform running with an Intel chip. (And in fact, it was
broken long before on many other architectures. For example, m68k has
long supported Amigas, Macintoshes, and other platforms.) The big
change in Linux 2.6 is that this feature and concept was standardized
so that all architectures handle this in a similar and saner way that
allows for more clear separation of the components that need
to be separated.</p>

<p>With this standardization comes two new
platforms to support for
i386. The first is NCR's Voyager architecture. This is a SMP system
(developed before the now-standard Intel MP specification) supporting
486-686 processors in up to 32x configurations. The actual number of
configurations that were sold with this architecture is relatively
small, and not all machines are supported yet. (The oldest ones are
unsupported.) The second architecture supported is the more widespread
PC-9800 platform developed by NEC into the (almost) dominant PC
platform in Japan until relatively recently. The original PC-9800
machines shipped with an 8086 processor and the line eventually evolved
and matured (in parallel with the AT-descendants) until they featured
Pentium-class processors and SMP support. (Of course, the support for
Linux is limited to 386 or better.) Although completely unknown in the
US, versions of Microsoft products up until Windows 95 were ported to
run on this hardware. The line has been officially discontinued by the
manufacturer in favor of more "standard" PCs.</p>

<p>By formalizing Linux's support for
these "slightly different"
hardware types, this will more easily allow the kernel to be
ported to other systems, such as dedicated storage hardware and other
components that use industry-dominant processor types. To be absolutely
clear
though, one should not take this subdivision too far. These
subarchitecture have been separated because very low-level components
of the system (such as IRQ routing) are slightly or radically
different. This is quite different than running Linux on an X-Box, for
example, where relatively little other than hardware drivers and some
quirks separate the system from being a "generic" i386 system. Support
for the X-Box would not be a subarchitecture.
</p>
<h3>Hyperthreading</h3>
<p>Another major hardware advancement
supported under Linux 2.6 is
hyperthreading. This is the ability, currently only built into modern
Pentium 4 processors but applicable elsewhere, allows a single physical
processor to masquerade (at the hardware level) as two or more
processors. This allows for
performance boosts in some circumstances, but also adds scheduling
complexity and other issues. Key in the kernel's improved support for
this feature is that the scheduler now knows how to recognize and
optimize processor loads across both real and virtual processors within
a machine. In previous versions of Linux, it was quite possible to
overwork a single processor because it was not possible to factor in
the workload as a whole. One of the great things to note about this
feature is that Linux was ahead of the market curve on supporting this
new hardware feature transparently and intelligently. (Windows 2000
servers
can see the additional faux-processors, but does not recognize them as
virtual. Thus, you also require additional CPU licenses to take
advantage of the feature. It was not until the Windows XP release that
Microsoft completely supported this feature.)</p>
<h2>Linux Internals</h2>
<h3>Scalability Improvements</h3>
<p>In addition to the previously described
generic features such as
NUMA and hyperthreading, Linux 2.6 also has other changes for
Intel servers at the top of the food chain. First and foremost is
improved support for other new Intel hardware features including
Intel's PAE ("Physical Address Extension") which allows
most newer 32-bit x86 systems to access up to 64GB of RAM, but in a
paged mode. In addition, IRQ balancing has been significantly improved
on
multiprocessor systems through major improvements to Linux's APIC
support.
</p>

<p>In addition to just supporting new
hardware features, internal
limits have been also increased when
possible. For example, the number of unique users and groups on a Linux
system has
been bumped from 65,000 to over 4 billion. (16-bit to 32-bit), making
Linux more practical on large file and authentication servers.
Similarly, The
number of PIDs (Process IDs) before wraparound has been bumped up from
32,000 to 1 billion, improving application starting
performance on very busy or very long-lived systems. Although the
maximum number of open files has not been increased, Linux with the 2.6
kernel will no longer require you to set what the limit is in advance;
this number will self-scale. And finally, Linux 2.6 will include
improved 64-bit support on block devices that support it, even on
32-bit platforms such as i386. This allows for filesystems up to 16TB
on common hardware.
</p>

<p>Another major scalability improvement
in Linux 2.6 is that the
kernel itself can now not only support more types of devices, but also
support more devices of a single type. Under all iterations of Linux
(and indeed, most UNIX-derived operating systems), users and
applications running on a system communicate with the attached hardware
using numbered device nodes. (The entries in the "/dev" directory.)
These device nodes were limited to 255 "major" devices (generally, one
type of device gets one or more device nodes) and 255 "minor" numbers
(generally, specific devices of that type.) For example, the
"/dev/sda2" device (the second partition on the first detected SCSI
disk), gets a major number of 8, common for all SCSI devices, and a
minor number of 2 to indicate the second partition. Different device
types allocate their major and minor numbers differently, so it can't
be said with assurance how many devices you can have on a Linux system.
Unfortunately, this system breaks down badly on large systems where it
would be possible, for example, to have many more than 255 of any
specific device in a system. (Think large storage arrays, print farms,
etc.) Under Linux 2.6, these limitations have been eased to allow
for 4095 major device types and a more than a million subdevices per
type. This increase should be more than adequate to support high-end
systems for the time being.
</p>
<h3>Interactivity and Responsiveness</h3>
<p>In addition to just scaling up, another
priority with the new
release has been to make the system more responsive. This is useful not
only for the general desktop user (who always likes to see things
respond quickly), but also to more time-critical applications where
absolute preciseness is required to achieve the desired effect. Despite
these changes, Linux 2.6 will not be a "hard" Real Time OS, which has
very strict requirements for absolutely ensuring that actions happen
predictably, but the overall responsiveness improvements should appeal
to all classes of Linux users. (That said, there are external projects
which have unofficial patches to provide RTOS functionality. Those
projects could conceivably be made official in the next major
release.)</p>

<p>One of the key improvements in Linux
2.6, is that the kernel is
finally preemptible. In all
previous versions of Linux, the kernel itself cannot be interrupted
while it is processing. (On a system with multiple processors, this was
true on a per-CPU basis.) Under Linux 2.6, the kernel now can be
interrupted mid-task, so that other applications can continue to run
even when something low-level and complicated is going on in the
background. Of course, there are still times when the kernel cannot be
interrupted in its processing. In reality, most users never saw these
delays, which are rarely over small fractions of a second. Despite
that, many users may notice an improvement in interactive performance
with this feature enabled; things like user input will "feel" faster,
even when the system is bogged down.</p>

<p>Linux's Input/Output (I/O) subsystems
has also undergone major
changes to allow them
to be more responsive under all sorts of workloads. These changes
include a complete rewrite of the I/O scheduler, the code
of the kernel that determines what processes get to read from devices
and when. The newly rewritten layer is now better capable of ensuring
that no processes get stuck waiting in line for too long, while
still allowing for the older optimizations which made sure that reading
data still happens in the most efficient way for the underlying
hardware.</p>

<p>On the application software side,
another change that will help make
Linux programs more responsive (if they use the feature) is support for
new "futexes" (or "Fast User-Space Mutexes") Futexes are a way in which
multiple processes or threads can
serialize events so that they don't trample on each other (a "race
condition"). Unlike the traditional mutex operations that most
threading libraries support, this concept is partially kernel based
(but only
in the contention case) and it also supports setting priorities to
allow applications or threads of higher priority access to the
contested resource first. By allowing a program to prioritize
waiting tasks, applications can be made to be more responsive in
timing-critical areas.
</p>

<p>In addition to all of the above, there
have been a number of other
smaller changes which will improve interactivity and performance in
many cases. These include more removals of the "Big Kernel Lock"
(non-fine-grained locks which were used in the early days' of Linux's
support for multiple processors), optimizations of filesystem
readahead, writeback, and manipulating small files, and other similar
changes.
</p>
<h3>Other Improvements</h3>
<p>
Linux, like the Open Source movement in general, has always been a
flag-bearer for the benefits of open standards. Another major change in
the 2.6 release, is that the kernel's internal
threading infrastructure has been rewritten to allow the Native POSIX
Thread Library (NPTL) to run on top of it. This can be a major
performance
boost for Pentium Pro and better processors in heavily threaded
applications, and many of the top players in the "enterprise" space
have
been clamoring for it. (In fact, Red Hat has already backported the
support to
Linux 2.4 and includes it starting with Red Hat 9 and Advanced Server
3.0) This change includes new
concepts to the Linux thread space including thread groups, local
memory for individual threads, POSIX-style signals, and other changes.
One of the major drawbacks is that applications (such as some versions
of Sun Java) not
written to spec that rely on old Linux-isms will break with the new
support enabled. As the benefits overwhelm the cost (and with so many
large players in the game), it's clear that most important applications
will support the changes before too long after the new kernel is
released.</p>
<h2>Module Subsystem and the Unified Device Model
</h2>
<p>Increasingly in modern operating
systems, the device handling
subsystems have taken on new prominence as they are forced to deal with
a myriad of internal and external bus types and more devices by more
vendors than you can shake a stick at. It should come as no surprise
then, that the upcoming upgrade to the Linux kernel will include
improved support both in its module loader, but also in its internal
understanding of the hardware itself. These changes range from the
purely cosmetic (driver modules now use a ".ko" extension, for "kernel
object", instead of just ".o") to a complete overhaul of the unified
device model. Throughout all of these changes is an emphasis on
stability and better grasp of the limitations of the previous revision.
</p>

<p>Strictly in the module (driver)
subsystem, there are a handful of
major changes to improve stability. The process for unloading modules
have been changed somewhat to reduce cases where it is possible for
modules to be used while they are still being unloaded, often causing a
crash. For systems where this problem cannot be risked, it is now even
possible to disable unloading of modules altogether. Additionally,
there has been extensive effort to standardize the process by which
modules determine and announce what hardware they support. Under
previous versions of Linux, the module would "know" what devices it
supported, but this information was not generally available outside of
the module itself. This change will allow hardware management software,
such as Red Hat's
"kudzu", to make intelligent choices even on hardware that would not
otherwise recognize. Of course, in the event that you know better than
the current version of
the driver what it supports, it is still possible to force a driver to
try to work on a specific
device.
</p>

<p>Outside of just module loading, the
device model itself has
undergone significant changes in the updated kernel release. Unlike the
module loader, which just has to concern itself with detecting the
resource requirements of incoming hardware, the device model is a
deeper concept which must be completely responsible for all of the
hardware in the system. Linux versions 2.2 and earlier had
only the barest support for a unified device model, preferring instead
to leave almost all knowledge of the hardware solely at the module
level. This worked fine, but in order to use all of the features of
modern hardware (especially ACPI), a system needs to know more than
just what resources a device uses: it needs to know things like what
bus it is connected to, what subdevices it has, what its power state
is, whether it can be reconfigured to use other resources in the event
of contention, and even to know about devices that haven't had modules
loaded for them yet. Linux 2.4 expanded on this foundation to become
the first
edition to unify the interfaces for
PCI, PC Card, and ISA Plug-and-Play buses into a single device
structure with
a common interface. Linux 2.6, through its new kernel object
("kobject") subsystem, takes this support to a new level by not only
expanding
to know about all devices in a system, but also to provide a
centralized interface for the important little details like reference
counting, power management, and exports to user-space.
</p>

<p>Now that an extensive amount of
hardware information is available
within the kernel, this has
allowed Linux to better support modern laptop and desktop features that
require a much more in-depth knowledge of
hardware. The most readily apparent application of this is the
increasing proliferation of so called "hot plug" devices like PC Cards,
USB and Firewire devices, and hot-plug PCI. While it's hard to think
back that far now, Linux didn't offer true support for any of these
devices until the 2.2 kernel. Given that hot-plugging is the rule these
days and not the exception, it is fitting that the new device
infrastructure essentially eliminates the differences between a
hot-plug and a legacy device. Since the kernel subsystem does not
directly differentiate between a device discovered at boot time from
one discovered later, much of the
infrastructure for dealing with pluggable devices has been simplified.
A second up and coming driver of this newly rewritten subsystem is for
improved support of modern power management. The new power management
standard in
recent years, called ACPI for "Advanced Configuration and Power
Interface", was first supported in rough form for the previous version
of the kernel. Unlike old-fashioned APM ("Advanced Power Management"),
OSes run on systems with this new interface are required to
individually tell all
compatible devices that they need to change their power
states. Without a centralized understanding of hardware, it would be
impossible for the kernel to know what devices it needs to
coordinate with and in what order. Although these are just two obvious
examples, there are clearly other areas (such as hardware auditing and
monitoring) that will benefit from a centralized picture of the world.</p>

<p>The final, but possibly the most
obvious, ramification of the new
centralized infrastructure is the creation of a new "system" filesystem
(to join 'proc'
for processes, 'devfs' for devices, and 'devpts' for UNIX98
pseudo-terminals) called 'sysfs'. This filesystem (intended to be
mounted on '/sys') is a visible representation of the device tree as
the kernel sees it (with some exceptions). This representation
generally includes a number of known attributes of the detected
devices, including the name of the device, its IRQ and DMA resources,
power status, and that sort of thing. However, one aspect of this
change that may be confusing on the short term is that many of the
device-specific uses of the "/proc/sys" directory may be moved into
this new filesystem. This change has not (yet) been applied
consistently, so there may continue to be an adjustment period.
</p>
<h2>System Hardware Support
</h2>
<p>As Linux has moved forward over the
years and into the mainstream,
each new iteration of the kernel appeared to be leaps and bounds better
than
the previous in terms of what types of devices it could support-- both
in
terms of emerging technologies (USB in 2.4) and older "legacy"
technologies (MCA in 2.2). As we arrive at the 2.6 however, the number
of major devices that Linux does not support is
relatively small. There are few, if any, major branches of the PC
hardware universe yet to conquer. It is for that reason that most (but
certainly not all) of improvements in i386 hardware support have been
to add robustness rather
than new features.
</p>
<h3>Internal Devices</h3>
<p>Arguably as important as the processor
type, the underling bus(es)
in a
system are the glue that holds things together. The PC world has been
blessed with no shortness of these bus technologies, from the oldest
ISA (found in the original IBM PC) to modern external serial and
wireless buses. Linux has always been quick to adapt to a new bus and
device type as they have become popular with consumer devices, but
significantly less quick adapting to technologies that get relatively
little use.</p>

<p>Improvements in Linux's support for
internal devices are really
spread across the board. One specific example where Linux is playing
"catch up" is support for the old ISA ("Industry Standard
Architecture") Plug-and-Play extensions. Linux didn't offer any
built-in support for PnP at all until the 2.4 release. This support has
been rounded out with the upcoming kernel to include full PnP BIOS
support, a device name database, and other compatibility changes. The
sum of all of those modifications, is that now Linux is now a
"true" Plug-and-Play OS and may be set as such in a compatible
machine's BIOS. Other legacy buses such as MCA ("Microchannel
Architecture") and EISA ("Extended ISA") have also been wrapped into
the new device model and feature device naming databases. On a more
modern front Linux 2.6 brings to the table a number of incremental
improvements to its PCI ("Peripheral Component Interconnect") subsystem
including improved Hot-Plug PCI and power management, support for
multiple AGPs ("accelerated graphics ports" -- a separate high-speed
extension to the PCI bus), and other changes. And finally, in addition
to all of the "real" buses, Linux 2.6 has internally added the concept
of a "legacy" bus that is specific to each architecture and contains
all of the assumed
devices that you would expect to find. On a PC, for example, this may
include on-board serial, parallel, and PS/2 ports-- devices that exist
but are not enumerated by any real buses on the system. This support
may require more complicated work
(such as querying firmware) on some platforms, but in general this is
just a wrapper to ensure that all devices are handled in a standard way
in the new driver
paradigm.</p>
<h3>External Devices
</h3>
<p>While it is true that the older-style
internal device buses have
not seen many new features during the most recent development cycle,
the same cannot be said for hot new external hardware. Possibly the
most important change in this space is the new support for USB 2.0
devices. These devices, commonly referred to as
"high speed" USB devices, support device bandwidth of up to 480
megabits per second, compared to 12 Mbit/sec of current USB. A related
new standard, USB
On-the-Go (or USB OTG), a point-to-point variant on the USB protocol
for connecting devices directly together (for example, to connect a
digital camera to a printer without having a PC in the middle) is not
currently supported in Linux 2.6. (Patches for this feature are
available, but not yet rolled into the official release.) In addition
to device support, much of the way USB devices have been internally
enumerated has been revised so that it is now possible to have many
more devices of the same type all accessible from within Linux. In
addition to the large changes, there has been an emphasis placed in
this development cycle on simplification, stability, and compatibility
that should improve the support of USB devices for all Linux users.
</p>

<p>On the complete opposite end of the
field, Linux 2.6 for the first
time includes support that allows a Linux-powered machine to be a USB
device, rather than a USB host. This would allow, for example, your
Linux-powered PDA to be plugged
into your PC and to have both ends of the line speaking the proper
protocol. Much of this support is new, but this is an essential
direction for Linux to move into for embedded devices.
</p>
<h3>Wireless Devices</h3>
<p>Wireless technology has really taken
off within the public in the
past several years. It often seems as if cords (except power... maybe?)
will be
a thing of the past within a handful of years. Wireless devices
encompass both networking devices (the most common currently) and also
more generic devices such as PDAs, etc. </p>

<p>In the wireless networking space,
devices can generally be divided
into long range (for example, AX.25 over amateur radio devices) and
short range (usually 802.11, but some older protocols exist.) Support
for both of these has been a hallmark of Linux since the early days
(v1.2) and both of these subsystems have been updated during
development of 2.6. The largest change here is that major components of
the short range subsystems for the various supported cards and
protocols has been merged into a single "wireless" subsystem and API.
This merge resolves a number of minor incompatibilities in the way
different devices have been handled and strengthens Linux's support for
the subsystem by making a central set of userspace tools that will work
with all supported devices. In addition to just standardization, Linux
2.6 introduces a number of overall improvements including better
capability to notify in the event of a state change (such as a device
that has a "roaming" state) and a change to TCP to better handle
periodic delay spikes which occur with wireless devices. Due to the
immediate desire to better support wireless devices in the current
Linux 2.4 kernel, many of these
changes have already been back-ported and are available for use.</p>

<p>In the generic wireless devices space,
there have been similar major
advancements. IrDA (the infrared protocol named for the Infrared Data
Associates group) has received some advancements since the last major
release such as power management and integration into the new kernel
driver model. The real advancements however have been made in providing
Linux
support for Bluetooth devices. Bluetooth is a new wireless protocol
that is designed to be short range and low on power consumption, but
does not have the line of sight limitations that IrDA has. Bluetooth as
a protocol is designed to go "anywhere" and has been implemented in
devices like PDAs, cell phones, printers, and more bizarre things such
as automotive equipment. The protocol itself is made up of two
different data link types: SCO, or "Synchronous Connection Oriented",
for lossy audio applications; and L2CAP, or "Logical Link Control and
Adaptation Protocol", for a more robust connection supporting
retransmits, etc. The L2CAP protocol further supports various
sub-protocols (including RFCOMM for point-to-point networking and BNEP
for Ethernet-like networking.) Linux's support for the things that
Bluetooth can do continues to grow and we can expect this to mature
significantly once more devices are in the hands of the consumers. It
should also be mentioned that initial support for Bluetooth has been
integrated into later editions of the 2.4 kernel.</p>
<h2>Block Device Support</h2>
<h3>Storage buses</h3>
<p>Dedicated storage buses, such as
IDE/ATA ("Integrated Drive
Electronics/Advanced Technology Attachment") and SCSI ("Small Computer
System Interface"), have also
received a major update during the 2.6 cycle. The most major
changes are centered around the IDE subsystem which has been rewritten
(and
rewritten again) during the development of the new kernel, resolving
many scalability problems and other limitations. For example, IDE CD/RW
drives can now be written to directly through the real IDE disk driver,
a much cleaner implementation than before. (Previously, it was required
to also use a special SCSI-emulating driver which was confusing and
often difficult.) In addition, new support has been added for
high-speed Serial ATA (S-ATA) devices, which have transfer rates
exceeding 150 MB/sec. On the SCSI side, there have also been many small
improvements scattered around the system both for wider support and
scalability. One specific improvement for older systems is that Linux
now supports SCSI-2 multipath devices that have more than 2 LUNs on a
device. (SCSI-2 is the previous version of the SCSI device standard,
circa 1994.) Another important change is that Linux can now fall back
to test media changing like Microsoft Windows does, to be more
compatible with devices that do not completely follow the
specification. As these technologies have stabilized over time, so too
has Linux's support for them.</p>

<p>Although not a storage bus in itself,
Linux now includes support for
accessing a newer machine's EDD ("Enhanced Disk Device") BIOS directly
to
see how the server views its own disk devices. The EDD BIOS includes
information on all of the storage buses which are attached to the
system that the BIOS knows about (including both IDE and SCSI.) In
addition to just getting configuration and other information out of the
attached devices, this provides several other advantages. For example,
this new interface allows Linux to know what disk device the system was
booted from, which is useful on newer systems where it is often not
obvious. This allows intelligent installation programs to consider that
information when trying to determine where to put the Linux boot
loader, for example. </p>

<p>In addition to all of these changes, it
should be stressed again
that all of the bus device types (hardware, wireless, and storage) have
been integrated into Linux's new device model subsystem. In some cases,
these changes are purely cosmetic. In other cases, there are more
significant changes involved (in some cases for example, even logic for
how devices are detected needed to be modified.)</p>
<h3>Filesystems</h3>
<p>The most obvious use of a block device
on a Linux (or any other)
system is by creating a filesystem on it, and Linux's support for
filesystems have been vastly improved since Linux 2.4 in a number of
respects. Key among these changes include support for extended
attributes and POSIX-style access controls.</p>

<p>When dealing strictly with conventional
Linux filesystems, the
extended filesystems (either "ext2" or "ext3") are the
systems most associated with a core Linux system. (ReiserFS is the
third most common option.) As these are the filesystems that users care
about the most, they have also been the most improved
during the development of Linux 2.6. Principal among these changes is
support for "extended attributes", or metadata that can be embedded
inside the filesystem itself for a specific file. Some of these
extended attributes will be used by the system and readable and
writable by root only. Many other operating systems, such as Windows
and the MacOS, already make heavy use of these kinds of attributes.
Unfortunately, the UNIX legacy of operating systems have not generally
included good support for these attributes and many user-space
utilities (such as 'tar') will need to be updated before they will
save and restore this additional information. The first real use of the
new extended attribute subsystem is to
implement POSIX access control lists, a
superset of standard UNIX permissions that allows for more fine-grained
control. In addition to these changes for ext3, there are several other
smaller changes: the journal commit time for the filesystem can now be
tuned to be more suited for laptop users (which might have to spin up
the drive if it were in a power save mode.), default mount options can
now also be stored within the filesystem itself (so that you don't need
to pass them at mount time), and you can now mark a directory as
"indexed" to speed up searches of files in the directory.
</p>

<p>In addition to the classic Linux
filesystems, the new kernel offers
full support for the new (on Linux) XFS filesystem. This filesystem is
derived from and is block-level compatible with the XFS filesystem used
by default on Irix systems. Like the extended filesystems and Reiser,
it can be used as a root-disk filesystem and even supports the newer
features such as extended attributes and ACLs. Many distributions are
beginning to offer support for this filesystem on their Linux 2.4-based
distributions, but it remains to be seen yet what place this filesystem
will have in the already crowded pantheon of UNIX-style filesystems
under Linux.
</p>

<p>Outside of those, Linux has also made a
number of improvements both
inside and outside the filesystem layer
to improve compatibility with the dominant PC operating systems. To
begin with, Linux 2.6 now supports Windows' Logical Disk Manager (aka
"Dynamic Disks"). This is the new partition table scheme that Windows
2000 and later have adopted to allow for easier resizing and creation
of
multiple partitions. (Of course, it is not likely that Linux systems
will be using this scheme for new installations anytime soon.) Linux
2.6 also features improved (and rewritten) support for the NTFS
filesystem and it is now
possible to mount a NTFS volume read/write. (Writing support is still
experimental and is gradually being improved; it may or may not be
enabled for the final kernel release.) And finally, Linux's support for
FAT12 (the DOS filesystem used on really old systems and floppy disks)
has been improved to work around bugs present in some MP3 players which
use that format. Although not as dominant in the marketplace, Linux has
also improved compatibility with OS/2 by adding extended attribute
support into the HPFS filesystem. Like previous releases, the new
additions to Linux 2.6 demonstrate the importance of playing well with
others and reinforces Linux's position as a "Swiss Army Knife"
operating system. </p>

<p>In addition to these changes, there
have been a large number of more
scattered changes in Linux's filesystem support. Quota support has been
rewritten to allow for the larger number of users supported on a
system. Individual directories can now be marked as synchronous so that
all changes (additional files, etc.) will be atomic. (This is most
useful for mail systems and directory-based databases, in addition to
slightly better recovery in the event of a disk failure.) Transparent
compression (a Linux-only extension) has been added to the ISO9660
filesystem (the filesystem used on CD-ROMs.) And finally, a new
memory-based filesystem ("hugetlbfs") has been created exclusively to
better support shared memory databases. </p>
<h2>Input / Output Support
</h2>
<p>On the more "external" side of any
computer system is the input and
output devices, the bits that never quite seem as important as they
are.
These include the obvious things like mice and keyboards, sound and
video cards, and less obvious things like joysticks and accessibility
devices. Many of Linux's end-user subsystems have been expanded during
the 2.6 development cycle, but support for most of the common devices
were already pretty
mature. Largely, Linux 2.6's improved support for these devices are
derived directly from the more general improvments with external
bus support, such as the ability to use Bluetooth wireless keyboards
and similar. There are
however a number of areas where Linux has made larger improvements.</p>
<h3>Human Interface Devices</h3>
<p>One major internal change in Linux 2.6
is the reworking of much of
the human interface layer. The human interface layer is the center of
the user experience of a Linux system, including the video output,
mice, and keyboards. In the new version of the kernel, this layer has
been reworked and modularized to a much greater extent than ever
before. It is now possible to create a completely "headless" Linux
system without any included support for a display or anything. The
primary benefit of this modularity may be for embedded developers
making devices that can only be administrated over the network or
serial, but end-users benefit as many of the underlying assumptions
about devices and architectures has been modularized out. For example,
it was previously always assumed that if you had a PC that you would
need support for a standard AT (i8042) keyboard controller; the new
version of Linux removes this requirement so that unnecessary code can
be kept out of legacy-less systems.</p>

<p>Support of Linux's handling of monitor
output has also received a
number of changes, although most of these are useful only in
configurations that make use of the kernel's internal framebuffer
console subsystem. (Most Intel Linux boxes are not configured this way,
but that is not the case for many other architectures.) In my personal
opinion, the best feature is that the boot logo (a cute penguin, if
you've never seen it) now supports resolutions up to 24bpp. That aside,
other new features for the console include resizing and rotating (for
PDAs and similar) and expanded acceleration support for more hardware.
And finally, Linux has now included kernel support for querying VESA
("Video Electronics Standard Association") monitors for capability
information, although XFree86 and most
distributions installation systems already have covered this detail in
user-space.</p>

<p>In addition to the big changes, Linux
2.6 also includes a number of
smaller changes for human interaction. Touch screens, for example, are
now supported. The mouse and keyboard drivers have also been updated
and standardized to only export a single device node
("/dev/input/mouse0", for example) regardless of the underlying
hardware
or protocol. Bizarre mice (with multiple scroll wheels, for example)
are now also supported. PC keyboard key mappings have also been updated
to follow the Windows "standard" for extended keys. Joystick support
has also been improved thanks not only to the addition of many new
drivers (including the X Box gamepad), but also to include newer
features such as force-feedback. And finally (but not least important),
the new release also includes support for the Tieman Voyager braille
TTY device to allow blind users better access to Linux. (This feature
is important enough that it has been back-ported to Linux 2.4 already.)</p>

<p>As a side note, Linux has also changed
the "system request"
interface to better support systems without a local keyboard. The
system request ("sysrq") interface is a method for systems
administrators at the local console to get debugging information, force
a system reboot, remount filesystems read-only, and do other wizardly
things. Since Linux 2.6 now supports a completely headless system, it
is now also possible to trigger these events using the /proc
filesystem. (Of course, if your system hangs and you need to force it
to do things, this may not be of much help to you.)</p>
<h3>Audio &amp; Multimedia
</h3>
<p>One of the most anticipated new
features of Linux 2.6 for desktop
users is the inclusion of ALSA (the "Advanced Linux Sound
Architecture") in lieu of the older sound system. The older system,
known as OSS for "Open Sound System", has served Linux since the early
days but had many architectural limitations. The first major
improvement with the new system is that it has been designed from the
start to be completely thread and SMP-safe, fixing problems with many
of the old drivers where they would not work properly outside the
expected "desktop-means-single-cpu paradigm." More importantly, the
drivers have been designed to be modular from the start (users of older
versions of Linux will remember that modularity was retro-fitted onto
the sound system around Linux 2.2), and that this allows for improved
support for systems with multiple sound cards, including multiple types
of sound cards. Regardless of how pretty the internals are, the system
would not be an improvement for users if it did not have neat new
whiz-bang features, and the new sound system has many of those. Key
among them are support for newer hardware (including USB audio and MIDI
devices), full-duplex playback and recording, hardware and
non-interleaved mixing, support for "merging" sound devices, and other
things. Whether you are an audiophile or just someone that likes to
play MP3s, Linux's improved sound support should be a welcome step
forward.</p>

<p>Beyond simple audio these days, what
users want is support for the
really fancy hardware like webcams, radio and TV adapters, and digital
video recorders. In all three cases, Linux's support has been improved
with the 2.6 release. While Linux has supported (to a greater or lesser
extent) radio
cards (often through userspace) for many iterations, support for
television tuners and video cameras was only added within the last one
or two major revisions. That subsystem, known as Video4Linux (V4L), has
received a major upgrade during the work on the new edition of the
kernel including both an API cleanup and support for more functionality
on the cards. The new API is not compatible with the previous one and
applications supporting it will need to upgrade with the kernel. And on
a completely new track, Linux 2.6 includes the first built-in
support for Digital Video Broadcasting (DVB) hardware. This type of
hardware, common in set-top boxes, can be used to make a Linux server
into a Tivo-like device, with the appropriate software. </p>
<h2>Software Improvements</h2>
<h3>Networking</h3>
<p>Leading-edge networking infrastructure
has always been one of
Linux's prime assets. Linux as an OS already supports most of the
world's dominant network protocols including TCP/IP (v4 and v6),
AppleTalk, IPX, and others. (The only unsupported one that comes to
mind is IBM/Microsoft's obsolete and tangled NetBEUI protocol.) Like
many of the changes in the other subsystems, most networking
hardware changes with Linux 2.6 are under the hood and not immediately
obvious. This includes low-level changes to take advantage of the
device model and updates to many of the device drivers. For example,
Linux now includes a separate MII (Media Independent Interface, or IEEE
802.3u) subsystem which is used by a number of the network device
drivers. This new subsystem replaces many instances where each driver
was handling that device's MII support in slightly different ways and
with duplicated code and effort. Other changes include major ISDN
updates and other things.</p>

<p>On the software side, one of the most
major changes is Linux's new
support for the IPsec protocols. IPsec, or IP Security, is a collection
of protocols for IPv4 ("normal" IP) and IPv6 that allow for
cryptographic security at the network protocol level. And since the
security is at the protocol level, applications do not have to be
explicitly aware of it. This is similar to SSL and other
tunneling/security protocols, but at a much lower level. Currently
supported in-kernel encryption includes various flavors of SHA ("secure
hash algorithm"), DES ("data encryption standard"), and others.</p>

<p>Elsewhere on the protocol side, Linux
has improved its support for
multicast networking. Multicast networks are networks where a single
sent packet is intended to be received by multiple computers. (Compare
to traditional point-to-point networks where you are only speaking to
one at a time.) Primarily, this functionality is used by messaging
systems (such as Tibco) and audio/video conferencing software. Linux
2.6 improves on this by now supporting several new SSM (Source Specific
Multicast) protocols, including MLDv2 (Multicast Listener Discovery)
and IGMPv3 (Internet Group Messaging Protocol.) These are standard
protocols that are supported by most high-end networking hardware
vendors, such as Cisco. </p>

<p>Linux 2.6 also has broken out a
separate LLC stack. LLC, or Logical
Link Control protocol (IEEE 802.2), is a low-level protocol that is
used beneath several common higher-level network protocols such as
Microsoft's NetBeui, IPX, and AppleTalk. As part of this change-over,
the IPX, AppleTalk, and Token Ring drivers have been rewritten to take
advantage of the new common subsystem. In addition, an outside source
has put together a working NetBEUI stack and it remains to be seen
whether it will ever be integrated into the stock kernel.</p>

<p>In addition to these changes, there
have been a number of smaller
changes. IPv6 has received some major changes and it can now also run
on Token Ring networks. Linux's NAT/masquerading support has been
extended to better handle protocols that require multiple connections
(H.323, PPTP, etc.) On the Linux-as-a-router front, support for
configuring
VLANs on Linux has been made no longer "experimental".</p>
<h3>Network Filesystems</h3>
<p>Overlaid on top of Linux's robust
support for network protocols is
Linux's equally robust support for network filesystems. Mounting (and
sometimes exporting) a network filesystem is one of the very few
high-level network operations that the kernel cares about directly.
(The most obvious other, the "network block device", did not receive
many changes for 2.6 and is generally used in specialized applications
where you end up doing something filesystem-like with it anyway.) All
other network operations are content to be relegated to user-space and
outside the domain of the kernel developers.</p>

<p>In the Linux and UNIX-clone world, the
most common of the network
filesystems is the aptly named Network File System, or NFS. NFS is a
complicated file sharing protocol that has deep roots in UNIX (and
especially Sun Solaris' excellent implementation). The primary
transport protocol can utilize either TCP or UDP, but several
additional sub-protocols are also required, each of which also run on
top of the separate RPC ("remote procedure call") protocol. These
include the separate "mount" protocol for authentication and NLM
("network lock manager") for file locking. (The common implementation
is also tied closely to other common RPC-based protocols, including
NIS-- "network information service"-- for authentication. NIS and its
progeny are not
commonly used for authentication on Linux machines due to fundamental
insecurities.) It is perhaps because of this complexity that NFS has
not been widely adapted as an "Internet" protocol.
</p>

<p>In Linux 2.6, this core Linux
filesystem received many updated and
improvements. The largest of these improvements is that Linux now
experimentally supports the new and not widely adopted NFSv4 protocol
version for both its client and server implementations. (Previous
versions of Linux included support for only the v2 and v3 versions of
the protocol.)
The new version supports stronger and more secure authentication (with
cryptography), more intelligent locking, support for
pseudo-filesystems, and other changes. Not all of the new NFSv4
features have been implemented in Linux yet, but the support is
relatively stable and could be used for some production applications.
In addition, Linux's NFS server implementation has been improved to be
more scalable (up to 64 times as many concurrent users and a larger
request queues), to be more complete (by supporting serving over TCP,
in addition to UDP), to be more robust (individual filesystems drivers
can adapt the way files on those systems are exported to suit their
particularities), and more easily maintainable (management though a new
'nfsd' filesystem, instead of system calls.) There have also been may
other under the hood changes, including separating lockd and nfsd, and
support for zero-copy networking on supported interfaces. NFS has also
been made somewhat easier to secure by allowing the kernel lockd port
numbers to be assigned by the administrator. The NFS
client side has also benefited from a number of improvements to the
implementation of the underlying RPC protocol including a caching
infrastructure, connection control over UDP, and other improvements for
TCP. Linux's support for using NFS-shared volumes as the root
filesystem (for disk-less systems) has also been improved as the kernel
now supports NFS over TCP for that purpose.</p>

<p>In addition to improving support for
the UNIX-style network
filesystems, Linux 2.6 also delivers many improvements to Windows-style
network filesystems. The standard shared filesystem for Windows servers
(as well as OS/2 and other operating systems) has been the SMB ("server
message block") protocol and the Linux kernel has had excellent client
support of the SMB protocol for many revisions. Windows 2000 however
standardized on an upgraded superset of the SMB protocol, known as CIFS
("common internet filesystem.") The intention of this major update was
to streamline and refine certain aspects of SMB which had at that point
become a complete mess. (The protocol itself was loosely defined and
often extended to the point that there were cases even where the
Win95/98/ME version was incompatible with the WinNT/Win2k version.)
CIFS delivered on that intention and added UNICODE support, improved
file locking, hard linking, eliminated the last vestiges of NetBIOS
dependencies, and added a few other features for Windows users. Since
Linux users do not like to be kept in the dark for long, Linux 2.6 now
includes completely rewritten support for mounting CIFS filesystems
natively. Linux 2.6 also now includes support for the SMB-UNIX
extensions to the SMB and CIFS protocols which allows Linux to access
non-Windows file types (such as device nodes and symbolic links) on SMB
servers which support it (such as Samba.) Although not as commonly seen
today, Linux has not completely
forgotten about the Novell NetWare users. Linux 2.6 now allows Linux
clients to mount up to the maximum of 256 shares on a single NetWare
volume using its built in NCP ("NetWare Core Protocol") filesystem
driver. </p>

<p>Linux 2.6 also includes improved
support for the relatively new
domain of distributed network filesystems, systems where files on a
single logical volume can be scattered across multiple nodes. In
addition to the CODA filesystem introduced in Linux 2.4, Linux now
includes some support for two other distributed filesystems: AFS and
InterMezzo. AFS, the Andrew filesystem (so named because it was
originally developed at CMU), is presently very limited and restricted
to read-only operations. (A more feature complete version of AFS is
available outside the kernel-proper.) The second newly supported
filesystem, InterMezzo (also developed at CMU), is also newly supported
under Linux 2.6 and it allows for more advanced features such as
disconnect operation (so you work on locally cached files) and is
suitable for high-availability applications where you need to guarantee
that storage is never unavailable (or faked, when down). It also has
applications for keeping data in sync between multiple computers, such
as a laptop or PDA and a desktop computer. Many of the projects
providing support for these new types of filesystems are initially
developed on Linux, putting Linux well ahead of the curve in support
for these new features.
</p>
<h2>Miscellaneous Features</h2>
<h3>Security</h3>
<p>Another of the big changes in Linux 2.6
that does not receive enough
attention is the wealth of new security-related changes. Most
fundamentally, the entirety of kernel-based security (powers of the
super user under a UNIX-like operating system) has been modularized out
to be one out of a potential number of alternate security modules. (At
present, however, the only offered security model is the default one and
an example how to make your own.) As part of this change, all parts of
the kernel have now been updated to use "capabilities" as the basis of
fine-grained user access, rather than the old "superuser" system.
Nearly all Linux systems will continue to have a "root" account which
has complete access, but this allows for a Linux-like system to be
created which does not have this underlying assumption. Another
security-related change is that binary modules (for example, drivers
shipped by a hardware manufacturer) can no longer "overload" system
calls with their own and can no longer see and modify the system call
table. This significantly restricts the amount of access that non-open
source modules can do in the kernel and possibly closes some legal
loopholes around the GPL. The final change that is somewhat
security-related is that Linux with the new kernel is now able to use
hardware random number generators (such as those present in some new
processors), rather than relying on a (admittedly quite good) entropy
pool based on random hardware fluctuations. </p>
<h3>Virtualizing Linux</h3>
<p>One of the most interesting new
features in Linux 2.6 is its
inclusion of a "user-mode" architecture. This is essentially a port
(like to a different hardware family) of Linux to itself, allowing for
a completely virtualized Linux-on-Linux environment to be run. The new
instance of Linux runs as if it was a normal application. "Inside" the
application, you can configure fake network interfaces, filesystems,
and other devices through special drivers which communicate up to the
host copy of Linux in a secure way. This has proved quite useful, both
for development purposes (profiling, etc.) as well as for security
analysis and honeypots. While most users will never need this kind of
support, it is an incredibly "cool" feature to have running on your
box. (Impress your friends!)</p>
<h3>Laptops</h3>
<p>In addition to all of the other general
purpose support described
above (improved APM and ACPI, wireless support improvements, etc.)
Linux also includes two other hard-to-classify features that will best
assist laptop users. The first is that the new edition of the kernel
now supports software-suspend-to-disk functionality for the Linux
user on the go. This feature still has some bugs to iron out, but is
looking solid for many configurations. The new version also supports
the ability of modern
mobile processors to change speed (and, in effect, power requirements)
based on
whether your system is plugged in or not.
</p>
<h3>Configuration Management
</h3>
<p>Linux 2.6 includes another feature
which might seem minor to some,
but will both greatly assist developers' abilities to debug kernel
problems of end-users as well as make it easier for individual
administators to know configuration details about multiple systems. In
short, the kernel now supports adding full configuration information
into the kernel file itself. This information would include details
such as what configuration options were selected, what compiler was
used, and other details which would help someone reproduce a similar
kernel if the need arose. This information would also be exposed to
users via the /proc interface.
</p>
<p> </p>
<h3>Legacy Support</h3>
<p>Although Linux 2.6 is a major upgrade,
the difference to user-mode
applications will be nearly non-existent. The one major exception to
this rule appears to be threading: some applications may do things that
worked under 2.4 or 2.2 but are no longer allowed. Those applications
should be the exception to the rule however. Of course, low-level
applications such as module utilities will definitely not work.
Additionally, some of the files and formats in the /proc and /dev
directories have changed and any applications that have dependencies on
this may not function correctly. (This is especially true as more
things shift over to the new "/sys" virtual filesystem. In the "/dev"
case,
backwards-compatible device names can easily be configured.) </p>

<p>In addition to those standard
disclaimers, there are a number of
other smaller changes which may affect some environments. First, very
old swap files (from Linux 2.0 or earlier) will need to be reformatted
before they can be used with 2.6. (Since swap files do not contain any
permanent data, that should not be a problem for any user.) The kHTTPd
daemon which allowed the kernel to serve web pages directly has also
been removed as most of the performance bottlenecks that prevented
Apache, Zeus, et. al. from reaching kernel speeds have been resolved.
Autodetection of DOS/Windows "disk managers" such as OnTrack and
EzDrive for large harddisk support with older BIOSes has been removed.
And finally,
support for using a special kernel-included boot sector for booting off
of a floppy disk has also been removed; you now need to use SysLinux
instead.
</p>
<h2>Stuff At The Bottom</h2>
<p>This document was assembled primarily
from long hours looking at
BitKeeper changelogs, looking at and playing with the source, reading
mailing list posts, and lots and lots of Google and Lycos searches for
documentation about this and that. As such, there are likely places
where something could have been missed or misunderstood, and places
where something could have been backed out after the fact. (I have been
especially careful of the two versions of IDE support that were worked
on during this time period, but there are other examples.) As a bit of
my research was done by looking at the web pages of various kernel
projects, I have had to be careful that the independent projects
weren't farther ahead with features than were accepted into the
mainline Linux code. If you see any
errors in this document or want to email me to ask me how my day is
going, you can do so at jpranevich &lt;at&gt; kniggit.net.</p>

<p>The newest version of this document can
always be found at <a href="http://kniggit.net/wwol26.html">http://kniggit.net/wwol26.html</a>.
</p>
<A NAME="translations"></A>
<h3>Translations</h3>
<p>Not an English speaker? This document
(or an older revision) has
been translated into a handful of other languages. 
</p>
<p>Bulgarian - <a href="http://kniggit.net/wwol26bg.html">http://kniggit.net/wwol26bg.html</a>
(Ivan Dimov)<br>
Chinese -
<a
 href="http://www-900.ibm.com/developerWorks/cn/linux/kernel/l-kernel26/index.shtml">http://www-900.ibm.com/developerWorks/cn/linux/kernel/l-kernel26/index.shtml</a>
(Stone Wang, et. al.)<br>
Czech - <a href="http://www.linuxzone.cz/index.phtml?ids=10&amp;idc=782">http://www.linuxzone.cz/index.phtml?ids=10&amp;idc=782</a>
(David
Haring)<br>
French - <a
 href="http://dsoulayrol.free.fr/articles/wonderful_2.6.html">http://dsoulayrol.free.fr/articles/wonderful_2.6.html</a>
(David
Soulayrol)<br>
Hungarian -
<a
 href="http://free.srv.hu/b/e/behun/pn/modules.php?op=modload&amp;name=News&amp;file=index&amp;catid=&amp;topic=12">http://free.srv.hu/b/e/behun/pn/modules.php?op=modload&amp;name=News&amp;file=index&amp;catid=&amp;topic=12</a>
(Ervin Novak)<span style="font-style: italic;"> (Not yet completed.)</span><br>
Italian - <a
 href="http://www.opensp.org/tutorial/vedi.php?appartenenza=42&amp;pagine=1">http://www.opensp.org/tutorial/vedi.php?appartenenza=42&amp;pagine=1</a>
(Giulio Ciuffi Vampa)<br>
Portuguese (BR) -
<a href="http://geocities.yahoo.com.br/cesarakg/wwol26-ptBR.html">http://geocities.yahoo.com.br/cesarakg/wwol26-ptBR.html</a>
(Cesar A. K.
Grossmann)<br>
Russian - <a
 href="http://www.opennet.ru/base/sys/linux26_intro.txt.html">http://www.opennet.ru/base/sys/linux26_intro.txt.html</a>
(Sergey Prokopenko)<br>
Spanish - <a href="http://www.escomposlinux.org/wwol26/wwol26.html">http://www.escomposlinux.org/wwol26/wwol26.html</a>
(Alex Fernández)
</p>
<p>An abridged version also appeared in
German in the 09/2003 issue of
LanLine magazine. I believe that an unabridged edition may be floating
around also, but I am uncertain of the link. If you know
of any additional translations to add to this list, please let me know.
</p>

<P> <SMALL><STRONG>Author's note: please send me a copy of any off-line
reprints of this article.</STRONG></SMALL></P>

</p>


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<img ALIGN="LEFT" ALT="[BIO]" SRC="../gx/2002/note.png">
<em>
I'm just this guy, y'know?  More info about me is on my
<A HREF="http://kniggit.net/">web page</A>.
</em>
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<p>
Copyright &copy; 2004, Joe Pranevich. Copying license 
<a href="http://linuxgazette.net/copying.html">http://linuxgazette.net/copying.html</a>
</p>

<p>
Published in Issue 98 of Linux Gazette, January 2004
</p>

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