Added DiskDump option to create mountable albeit unbootable disks: --forceBPB
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Jeff Parsons
Jeff Parsons
parent
61c1a3f211
commit
74617db812
3 changed files with 94 additions and 6 deletions
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@ -100,13 +100,25 @@ Another unexpected file was **BASICA.EXE** (54277 bytes) from 1999. It seems un
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*any* BASIC binary with this game, because DOS was a prerequisite, and at the time, all versions of DOS included BASIC.
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IBM's PC-DOS shipped with **BASICA.COM** and OEM versions of DOS shipped with either **GWBASIC.EXE** or **BASIC.EXE**.
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The closest matching binary I'd seen up to this point was **BASICA.EXE** from [COMPAQ DOS 1.12](/disks/pcx86/dos/compaq/1.12/)
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(54304 bytes). And sure enough, dumping the strings inside this **BASICA.EXE** revealed that it was a close relative:
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Curiously, the **BASICA.EXE** from [COMPAQ DOS 1.11](/disks/pcx86/dos/compaq/1.11/) is exactly 5 bytes smaller, and both
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files contain the following strings:
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The COMPAQ Personal Computer BASIC
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Version 1.13
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(C) Copyright COMPAQ Computer Corp. 1983
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In fact, the only differences are in first few and last few bytes:
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1c1
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< 00000000 4d 5a 05 00 6b 00 00 00 20 00 7a 03 ff ff 00 00 |MZ..k... .z.....|
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---
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> 00000000 4d 5a 20 01 6a 00 00 00 20 00 00 00 ff ff 00 00 |MZ .j... .......|
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3196,3197c3196
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< 0000d400 4d 73 44 6f 73 |MsDos|
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< 0000d405
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---
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> 0000d400
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It's safe to say that IBM would not have distributed a COMPAQ binary; if IBM had distributed any BASIC binary at all,
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it would have been their own **BASICA.COM**. Of course, the problem with IBM's **BASICA.COM** is that it also requires
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an IBM PC with ROM BASIC installed, which is why some people would have preferred the COMPAQ binary: it had no ROM
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@ -9,7 +9,9 @@ machines:
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resume: 1
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autoMount:
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A:
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path: /disks/pcx86/dos/compaq/1.11/COMPAQ-DOS111.json
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name: COMPAQ MS-DOS 1.11
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B:
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name: None
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---
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COMPAQ MS-DOS 1.11
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@ -20,10 +22,11 @@ Released in 1983 by COMPAQ Computer Corp, this early version of MS-DOS displays
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The COMPAQ Personal Computer DOS
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Version 1.11
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(C) Copyright COMPAQ Computer Corp. 1982
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(C) Copyright Microsoft 1981, 82
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A directory listing of the diskette is provided [below](#directory-of-compaq-ms-dos-111-diskette).
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A directory listing of the 320Kb diskette is provided [below](#directory-of-compaq-ms-dos-111-diskette).
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{% include machine.html id="ibm5150-compaq111" %}
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@ -67,4 +70,73 @@ A directory listing of the diskette is provided [below](#directory-of-compaq-ms-
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28 file(s) 256320 bytes
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53248 bytes free
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The boot sector of the COMPAQ MS-DOS 1.11 disk image (COMPAQ-DOS111.img) contained the following bytes:
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00000000 fa bc e7 01 b8 c0 07 8e d0 fb 8e d8 8e c0 33 c0 |..............3.|
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00000010 cd 13 b8 01 02 bb 00 02 b9 04 00 33 d2 e8 8b 00 |...........3....|
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00000020 eb 1c bb da 00 8a 07 3c 24 74 0c 53 b4 0e bb 07 |.......<$t.S....|
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00000030 00 cd 10 5b 43 eb ee 33 c0 cd 16 eb c3 c3 fc 8b |...[C..3........|
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00000040 f3 bf c4 00 b9 0b 00 f3 a6 75 d7 83 c6 15 b9 0b |.........u......|
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00000050 00 f3 a6 75 cd b8 01 02 bb 00 02 b9 02 00 33 d2 |...u..........3.|
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00000060 e8 48 00 8a 27 80 fc fe be 26 01 74 0a 80 fc ff |.H..'....&.t....|
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00000070 74 02 eb ae be 3c 01 b8 60 00 50 07 8b 04 33 db |t....<..`.P...3.|
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00000080 8b 4c 02 8b 54 04 e8 22 00 8b 44 06 03 5c 08 8b |.L..T.."..D..\..|
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00000090 4c 0a 8b 54 0c e8 13 00 8b 44 0e 03 5c 10 8b 4c |L..T.....D..\..L|
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000000a0 12 8b 54 14 e8 04 00 ff 2e 52 01 bf 05 00 57 50 |..T......R....WP|
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000000b0 cd 13 72 03 58 58 c3 33 c0 cd 13 58 5f 4f 75 ee |..r.XX.3...X_Ou.|
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000000c0 58 e9 5e ff 49 4f 53 59 53 20 20 20 43 4f 4d 4d |X.^.IOSYS COMM|
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000000d0 53 44 4f 53 20 20 20 43 4f 4d 0a 0d 4e 6f 6e 2d |SDOS COM..Non-|
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000000e0 53 79 73 74 65 6d 20 64 69 73 6b 20 6f 72 20 64 |System disk or d|
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000000f0 69 73 6b 20 65 72 72 6f 72 0a 0d 52 65 70 6c 61 |isk error..Repla|
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00000100 63 65 20 61 6e 64 20 73 74 72 69 6b 65 20 61 6e |ce and strike an|
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00000110 79 20 6b 65 79 20 77 68 65 6e 20 72 65 61 64 79 |y key when ready|
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00000120 0a 0d 24 47 41 53 01 02 08 00 00 00 08 02 00 02 |..$GAS..........|
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00000130 01 01 00 00 08 02 00 10 01 02 00 00 06 02 03 00 |................|
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00000140 00 01 08 02 00 0c 01 01 00 00 03 02 00 10 01 01 |................|
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00000150 00 01 00 00 60 00 28 43 29 43 6f 70 79 72 69 67 |....`.(C)Copyrig|
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00000160 68 74 20 43 4f 4d 50 41 51 20 43 6f 6d 70 75 74 |ht COMPAQ Comput|
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00000170 65 72 20 43 6f 72 70 6f 72 61 74 69 6f 6e 20 31 |er Corporation 1|
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00000180 39 38 32 00 00 00 00 00 00 00 00 00 00 00 00 00 |982.............|
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00000190 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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000001a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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000001b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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000001c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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000001d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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000001e0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
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Consequently, the disk could not be mounted by a modern operating system (e.g., macOS), because it lacked a proper
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BPB at offset 0x000B.
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Using the *--forceBPB* option of the [DiskDump](/modules/diskdump/) utility, I was able to create a mountable disk
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image with the following boot sector modifications:
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00000000 eb fe 90 50 43 4a 53 2e 4f 52 47 00 02 02 01 00 |...PCJS.ORG.....|
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00000010 02 70 00 80 02 ff 01 00 08 00 02 00 00 00 00 00 |.p..............|
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00000020 00 00 00 00 00 8a 07 3c 24 74 0c 53 b4 0e bb 07 |.......<$t.S....|
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These modifications included:
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- 0x0000-0x0002: 2-byte Intel JMP instruction followed by 1-byte Intel NOP
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- 0x0003-0x000A: 8-byte OEM signature string (we use the fake "PCJS.ORG" OEM signature)
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- 0x000B-0x001D: 19-byte BPB describing a 320Kb diskette image with 8 sectors/track and 2 heads
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Ordinarily, only the 19-byte BPB would be required, but it turned out that macOS wouldn't mount the image file
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*unless* the boot sector also began with an Intel JMP instruction. All known PC-DOS boot sectors begin with a JMP
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instruction, so these early OEM disk images were rather unusual.
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Anyway, I changed the *--forceBPB* option to update all 30 bytes at the beginning of the boot sector, making the disk
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image mountable, but also rendering it unbootable. But that was OK, because all I wanted to do with the image was mount
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it and copy its files. The sequence of commands were:
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diskdump --disk=COMPAQ-DOS111.img --format=json --output=COMPAQ-DOS111-BPB.json
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warning: BPB has been updated
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327680-byte disk image saved to COMPAQ-DOS111-BPB.json
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diskdump --disk=COMPAQ-DOS111.json --format=img --output=COMPAQ-DOS111-BPB.img
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327680-byte disk image saved to COMPAQ-DOS111-BPB.img
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chmod -w COMPAQ-DOS111-BPB.img
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open COMPAQ-DOS111-BPB.img
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mkdir COMPAQ-DOS111
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cp -pr /Volumes/Untitled/ COMPAQ-DOS111
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[Return to [COMPAQ MS-DOS Disks](/disks/pcx86/dos/compaq/)]
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@ -343,6 +343,7 @@ function DiskDump(sDiskPath, asExclude, sFormat, fComments, sSize, sServerRoot,
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this.sJSONWhitespace = (this.fJSONComments? " " : "");
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this.fXDFSupport = (argv && argv['xdf']);
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this.sLabel = (argv && argv['label']);
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this.forceBPB = (argv && argv['forcebpb']);
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/*
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* The dump operation itself doesn't care about sManifestFile, but we DO need some indication
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@ -2780,7 +2781,7 @@ DiskDump.prototype.convertToJSON = function()
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}
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}
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}
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else if (bByte0 == X86.OPCODE.JMPS && bByte1 >= 0x22) {
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else if (bByte0 == X86.OPCODE.JMPS && bByte1 >= 0x22 || this.forceBPB) {
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/*
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* I'm going to stick my neck out here and slam a BPB into this disk image, since it doesn't appear
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* to have one, which should make it more "mountable" on modern operating systems. PC-DOS 1.x (and
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@ -2792,8 +2793,11 @@ DiskDump.prototype.convertToJSON = function()
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* 0x003-0x00A. For example, the word at 0x006 contains the starting segment for where to load
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* IBMBIO.COM and IBMDOS.COM. Those same early boot sectors are also missing the traditional 0xAA55
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* signature at the end of the boot sector.
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*
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* However, if --forceBPB is specified, all those concerns go out the window: the goal is assumed to
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* be a mountable disk, not a bootable disk. So the BPB copy starts at offset 0 instead of SECTOR_BYTES.
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*/
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for (i = DiskAPI.BPB.SECTOR_BYTES; i < DiskAPI.BPB.LARGE_SECS+4; i++) {
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for (i = this.forceBPB? 0 : DiskAPI.BPB.SECTOR_BYTES; i < DiskAPI.BPB.LARGE_SECS+4; i++) {
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this.bufDisk.writeUInt8(DiskDump.aDefaultBPBs[iBPB][i] || 0, offBootSector + i);
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}
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console.log("warning: BPB has been updated");
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