Retro/pcjs
Watch
1
0
Fork
You've already forked pcjs
 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Added more info about DOS 2.0 BPBs

Browse source
This commit is contained in:
Jeff Parsons 2017-06-01 16:42:46 -07:00 • committed by Jeff Parsons
commit 20f8bdf141
2 changed files with 21 additions and 12 deletions
Download patch file Download diff file Expand all files Collapse all files

18
modules/shared/lib/diskapi.js
View file

@ -89,8 +89,9 @@ DiskAPI.DISK_FORMATS = {
1474560: [80,2,18,,0xF0], // media type 0xF0: 80 cylinders, 2 heads (double-sided), 18 sectors/track, (2880 total sectors x 512 bytes/sector == 1474560)
2949120: [80,2,36,,0xF0], // media type 0xF0: 80 cylinders, 2 heads (double-sided), 36 sectors/track, (5760 total sectors x 512 bytes/sector == 2949120)
/*
* The following are some common partition sizes, which we explicitly map to CHS values, since the MBR and/or BPB
* can mislead us when attempting to calculate total cylinders.
* The following are some common partition sizes, which we explicitly map to CHS values, since MBR/BPB values
* can mislead us when attempting to determine the exact disk geometry. TODO: Investigate. Is it possible that
* usable space on early hard disks was reduced to reserve the last cylinder for diagnostics, head parking, etc?
*/
10618368:[306,4,17], // PC XT 10Mb hard drive (type 3)
21368320:[615,4,17], // PC AT 20Mb hard drive (type 2)
@ -152,7 +153,14 @@ DiskAPI.BOOT = {
};
/*
* BIOS Parameter Block (BPB) offsets in DOS-compatible boot sectors (DOS 2.0 and up)
* BIOS Parameter Block (BPB) offsets in DOS-compatible boot sectors (DOS 2.x and up)
*
* NOTE: DOS 2.x OEM documentation says that the words starting at offset 0x018 (TRACK_SECS, TOTAL_HEADS, and HIDDEN_SECS)
* are optional, but even the DOS 2.0 FORMAT utility initializes all three of those words. There may be some OEM media out
* there with BPBs that are only valid up to offset 0x018, but I've not run across any media like that.
*
* DOS 3.20 added LARGE_SECS, but unfortunately, it was added as a 2-byte value at offset 0x01E. DOS 3.31 decided
* to make both HIDDEN_SECS and LARGE_SECS 4-byte values, which meant that LARGE_SECS had to move from 0x01E to 0x020.
*/
DiskAPI.BPB = {
SECTOR_BYTES: 0x00B, // 2 bytes: bytes per sector (eg, 0x200 or 512)
@ -165,8 +173,8 @@ DiskAPI.BPB = {
FAT_SECS: 0x016, // 2 bytes: sectors per FAT (eg, 1)
TRACK_SECS: 0x018, // 2 bytes: sectors per track (eg, 8)
TOTAL_HEADS: 0x01A, // 2 bytes: number of heads (eg, 1)
HIDDEN_SECS: 0x01C, // 4 bytes: number of hidden sectors (always 0 for non-partitioned media)
LARGE_SECS: 0x020 // 4 bytes: number of sectors if TOTAL_SECS is zero (TODO: Verify the true extent of DOS 2.0 BPBs; they may have stopped with HIDDEN_SECS, which is what DiskDump assumes)
HIDDEN_SECS: 0x01C, // 2 bytes (DOS 2.x) or 4 bytes (DOS 3.31 and up): number of hidden sectors (always 0 for non-partitioned media)
LARGE_SECS: 0x020 // 4 bytes (DOS 3.31 and up): number of sectors if TOTAL_SECS is zero
};
/*