1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
|
Floppy format descriptions
--------------------------
Notes:
Extra Tracks:
Many other variations upon these formats are possible. In particular,
many nominally 40-track or 80-track drives are capable of more tracks,
usually 41 and 83 respectively. Not all drives can seek to these
unofficial extra tracks, and even on drives which can these extra
tracks tend to be less reliable. However, most of the formats listed
below could be increased in capacity by using extra tracks.
Extra Sectors:
The official formats used by MS-DOS and other operating systems are
generally very conservative, and more sectors can nearly always be
fit onto each track by reducing the size of the gap between tracks
and/or the size of the leftover space at the end of the disk.
If the gap sizes are too small, it is necessary to use a 2:1
interleave to achieve acceptable performance.
Larger sectors:
By using larger sectors, quite a bit of space is saved as the
per-sector overhead in gaps and headers, permitting more data
to fit on a disk than could possibly be achieved with normal
512-byte sectors. However, MS-DOS and other operating systems
cannot normally read these formats. Furthermore, when any portion
of one of these larger sectors is read, the entire sector must be
read. When any portion of such a sector is written to, the entire
sector must be read, and then written back with just the necessary
portion modified. Both of these circumstances can entail worse
performance for small reads and (especially) small writes.
"2m" Formats:
"2m" formats have a "standard" density on the first side of the first
track, and a higher density on the rest of the disk. And are intended
only for MS-DOS file systems. The MS-DOS boot sector indicates the
number of sectors and tracks on the disk, and by this method 2m and
mtools can determine the geometry of the *rest* of the disk. To cover
up for the missing sectors on the first track, 2m and mtools pretend
that there is a duplicate FAT in the missing sectors, which it
simulates by using the first (real) FAT.
Linux is also capable of using non-2m formats with mixed sector sizes
(without using a reduced density on the first track. This is necessary
for using non-MS-DOS formats, such as ext2fs, tar, Minix, or cpio.
This can also be done for MS-DOS formats, but 2m can only read disks
with the "standard" format on the first side of the first track.
"Xdf" formats:
Just like "2m" formats, Xdf formats use mixed sector sizes.
However, for Xdf disks, the logical order of the sectors on a
given track, and their physical order is not the same. When
reading a track, sectors reads alternate between both
sides, instead of first one complete side and then the
other. This technique allows to do much faster accesses: 550
milliseconds per track instead of the 800 microseconds (or
more) needed for 2m. If you have any questions, please mail me
at Alain@knaff.lu
80/90/160/180 KB 5.25":
Original IBM PC, CP/M, Apple II, TRS-80, etc. Single density, FM
(not MFM), 40-track. Some systems also used "hard" sectoring, with
an index hole for each sector. These are probably readable on
standard FDCs if anyone cares to go to the effort. 160KB/180KB
formats were double-sided.
320 KB 5.25":
CP/M, Zenith Z-100, some forms of MS-DOS. 8-sector DD 40-track.
400 KB 5.25":
AT&T 7300/3B1: cpio format, 10 sectors, DS, 40 tracks.
PC: MS-DOS, 10 sectors, DS, 40 tracks; formatted by various
utilities; readable by some versions of MS-DOS.
<720KB 3.5" formats:
- Some dedicated word-processing systems use lower than normal
capacity floppies (some may be 40-track either via "stretching"
or by having odd drives; others may be single-sided or use fewer
sectors per track, or use "single density" or FM). IMHO these
are not worth supporting in the kernel per se, but providing
info on them for use via setfdprm is appreciated.
- Atari ST 360 KB floppies: these are 9 sector 250KBps 80-track
single-sided, using a slightly incompatible MS-DOS-like FAT.
Very common distribution format for Atari ST software.
- Mac 400 KB: single-sided 80-tracks, Mac MFS or HFS file system,
Group Code Recording, zone bit recording, variable RPMs from 300
to 600 in 5 zones, and auto-eject mechanism. Almost theoretically
impossible to read on "normal" drives without some form of hardware
assistance.
720 KB 3.5":
- PC: 9 sectors, DS, 80-track; very common.
- Atari ST: same as Atari ST 360 KB except double-sided.
720 KB 5.25":
- "Quad Density": 9 sectors, DS, 80-track; name is rather misleading,
as it is double density 80 track.
800 KB:
- PC: 10 sectors, DS, 80 tracks; readable by MS-DOS; formatted by
many PC utilities; "almost standard".
- Atari ST "Twister": 10 sectors, DS, 80-track; slightly incompatible
MS-DOS-like FAT; sector skewing (originated by David Small).
- Mac 800 KB: same as Mac 400KB except double-sided.
880 KB:
- PC: 11 sectors, DS, 80 tracks, interleaved(?). Formatted by various
PD utilities such as fdformat.
- Amiga: uses "single-sector" tracks the size of 11 sectors; DS; 80
tracks. Written by a custom chip rather than a standard FDC; it
is very difficult to read using a standard FDC, though writing or
formatting might be theoretically possible.
880 KB-960 KB:
Atari ST: 11/12 sectors, DS, 80-track, interleaved(?); not very
reliable, formatted by various PD utilities.
960 KB:
2m and Linux; 12 sectors interleaved(?), DS, 250Kbps?, 80-track,
1K sectors(?).
1001 KB:
"Japanese" format: 300Kbps, 77 tracks, HD drives/disks.
1040 KB:
2m and Linux only; 13 sectors, DS, 300Kbps, 80-track.
1120 KB:
2m and Linux only; 14 sectors interleaved, DS, 300Kbps, 80-track.
Can only be formatted under Linux; even under Linux difficult to
format on ED drives.
1200 KB 5.25" HD:
"AT": 360 rpm 500Kbps 80-track 15-sector MS-DOS.
1360 KB 5.25" HD:
Highest "fdformat" noninterleaved 5.25" format. 360 rpm 500Kbps
17-sector MS-DOS.
1440 KB 5.25" HD:
Interleaved 18-sector 360 rpm 500Kbps; highest "fdformat" 5.25" format.
18-sector MS-DOS.
2m and Linux only: noninterleaved 1024-byte sector 18-sector-equivalent
360 rpm 500Kbps; 18-sector MS-DOS. A good substitute for 1.44MB 3.5"
floppies.
1600 KB 5.25" HD:
2m and Linux only: interleaved? 500Kbps 80-track; 1 8KB sector, 1
2KB sector?
1760 KB 3.5" HD:
2m and Linux only: 11 1KB sectors; 500Kbps, noninterleaved?
1840 KB 3.5" HD:
2m and Linux only: 23-sector equivalent; 500Kbps, noninterleaved.
1920 KB 3.5" HD:
2m and Linux only: 3 4KB sectors; 500Kbps, interleaved?
2m and Linux only: 1 8KB sector, 1 4KB sector; 500Kbps, interleaved?
2880 KB 3.5" ED:
"Extra Density" or "Extra High Density". 1Mbps, 36-sector, DS, 80-
track.
3200 KB 3.5" ED:
Non-interleaved, 80 track, 40-sector 1Mbps. Highest capacity that
MS-DOS can read directly(?)
3520 KB 3.5" ED:
2m and Linux only: 1 16KB sector, 1 4KB sector, 1 2KB sector?
Non-interleaved, 80 track 1Mbps. Highest capacity that 2m can
format.
3840 KB 3.5" ED:
2m and Linux only: 1 16KB sector, 1 8KB sector (or is it 3 8KB
sectors?). Non-interleaved, 80 track 1Mbps. Formatted only by
Linux, but readable and writeable by 2m.
|
