MEMDISK: algorithmic determination of floppy formats

Consider all disks < 4 MB to be floppies, and guess their geometry
algorithmically.

1 files changed, 38 insertions, 19 deletions

diff --git a/doc/memdisk.txt b/doc/memdisk.txt
index 759a7b27..808a9476 100644
--- a/doc/memdisk.txt
+++ b/doc/memdisk.txt
@@ -28,25 +28,44 @@ Note the following:
 
 a) The disk image can be uncompressed or compressed with gzip or zip.
 
-b) If the disk image is one of the following sizes, it's assumed to be a
-   floppy image:
-
-     368,640 bytes -  360K floppy
-     737,280 bytes -  720K floppy
-   1,222,800 bytes - 1200K floppy
-   1,474,560 bytes - 1440K floppy
-   1,720,320 bytes - 1680K floppy (common extended format)
-   1,763,328 bytes - 1722K floppy (common extended format)
-   2,949,120 bytes - 2880K floppy
-   3,932,160 bytes - 3840K floppy (extended format)
-
-   For any other size, the image is assumed to be a hard disk image,
-   and should typically have an MBR and a partition table.  It may
-   optionally have a DOSEMU geometry header; in which case the header
-   is used to determine the C/H/S geometry of the disk.  Otherwise,
-   the geometry is determined by examining the partition table, so the
-   entire image should be partitioned for proper operation (it may be
-   divided between multiple partitions, however.)
+b) If the disk image is less than 4,194,304 bytes (4096K, 4 MB) it is
+   assumed to be a floppy image and MEMDISK will try to guess its
+   geometry based on the size of the file.  MEMDISK recognizes all the
+   standard floppy sizes as well as common extended formats:
+   
+     163,840 bytes  (160K) c=40 h=1 s=8		5.25" SSSD
+     184,320 bytes  (180K) c=40 h=1 s=9		5.25" SSSD
+     327,680 bytes  (320K) c=40 h=2 s=8		5.25" DSDD
+     368,640 bytes  (360K) c=40 h=2 s=9		5.25" DSDD
+     655,360 bytes  (640K) c=80 h=2 s=8		3.5"  DSDD
+     737,280 bytes  (720K) c=80 h=2 s=9		3.5"  DSDD
+   1,222,800 bytes (1200K) c=80 h=2 s=15	5.25" DSHD
+   1,474,560 bytes (1440K) c=80 h=2 s=18	3.5"  DSHD
+   1,638,400 bytes (1600K) c=80 h=2 s=20	3.5"  DSHD (extended)
+   1,720,320 bytes (1680K) c=80 h=2 s=21	3.5"  DSHD (extended)
+   1,763,328 bytes (1722K) c=82 h=2 s=21	3.5"  DSHD (extended)
+   1,784,832 bytes (1743K) c=83 h=2 s=21	3.5"  DSHD (extended)
+   1,802,240 bytes (1760K) c=80 h=2 s=22	3.5"  DSHD (extended)
+   1,884,160 bytes (1840K) c=80 h=2 s=23	3.5"  DSHD (extended)
+   1,966,080 bytes (1920K) c=80 h=2 s=24	3.5"  DSHD (extended)
+   2,949,120 bytes (2880K) c=80 h=2 s=36	3.5"  DSED
+   3,194,880 bytes (3120K) c=80 h=2 s=39	3.5"  DSED (extended)
+   3,276,800 bytes (3200K) c=80 h=2 s=40	3.5"  DSED (extended)
+   3,604,480 bytes (3520K) c=80 h=2 s=44	3.5"  DSED (extended)
+   3,932,160 bytes (3840K) c=80 h=2 s=48	3.5"  DSED (extended)
+
+   A small perl script is included in the MEMDISK directory which can
+   determine the geometry that MEMDISK would select for other sizes;
+   in general MEMDISK will correctly detect most physical extended
+   formats used, with 80 cylinders or slightly more.
+
+   If the image is 4 MB or larger, it is assumed to be a hard disk
+   image, and should typically have an MBR and a partition table.  It
+   may optionally have a DOSEMU geometry header; in which case the
+   header is used to determine the C/H/S geometry of the disk.
+   Otherwise, the geometry is determined by examining the partition
+   table, so the entire image should be partitioned for proper
+   operation (it may be divided between multiple partitions, however.)
 
    You can also specify the geometry manually with the following command
    line options: