---
layout: page
title: "PC-DOS 0.90 (with Debugger)"
permalink: /disks/pcx86/dos/ibm/0.90/debugger/
machines:
  - id: ibm5150-pcdos090
    type: pcx86
    debugger: true
    config: /devices/pcx86/machine/5150/mda/256kb/debugger/machine.xml
    resume: 1
    autoMount:
      A:
        path: /disks/pcx86/dos/ibm/0.90/PCDOS090.json
      B:
        name: None
---

PC-DOS 0.90 (with MDA and Debugger)
-----------------------------------

There was no PC-DOS 0.90 product *per se*.  It has been dubbed version 0.90 simply because it predates
[PC-DOS 1.00](../1.00/) by several months.  More information about this preliminary version of PC-DOS can
be found at the [OS/2 Museum](http://www.os2museum.com/wp/pc-dos-1-0-but-not-quite/).

Below is an IBM PC (Model 5150) with an original IBM ROM BIOS and Monochrome (MDA) Display that will boot PC-DOS 0.90.
The machine is configured to run at 4.77Mhz, so the ROM BIOS memory test has been disabled, since a PC with 256Kb
was rather slow to boot.  A similar configuration with [Color Display](/disks/pcx86/dos/ibm/0.90/) is also available.

{% include machine.html id="ibm5150-pcdos090" %}

PC-DOS 0.90 files were distributed on one single-sided (160Kb) diskette.  A directory listing of the disk is
provided below.

### Directory of PC-DOS 0.90 Diskette

	 Volume in drive A has no label
	 Directory of A:\
	
	IBMBIO   COM      2560 05-29-81  12:00a
	IBMDOS   COM      5566 05-29-81  12:00a
	COMMAND  COM      2576 05-29-81  12:00a
	DEBUG    COM      5450 05-27-81  12:00a
	TIME     COM       243 05-19-81  12:00a
	DATE     COM       245 05-20-81  12:00a
	ASM      COM      6389 05-15-81  12:00a
	FORMAT   COM      2048 05-29-81  12:00a
	HEX2BIN  COM       483 05-07-81  12:00a
	BASIC    COM     11008 06-04-81  12:00a
	CHKDSK   COM      1224 05-30-81  12:00a
	EDLIN    COM      2231 05-29-81  12:00a
	MODE     COM       675
	COMMENTS          3561 06-05-81  12:00a
	MOVBAS   COM       128 04-23-81  12:00a
	BAS18    COM     11008 06-04-81  12:00a
	BASICA   COM     14976 06-04-81  12:00a
	AUTOEXEC BAK        24
	SYS      COM       896 06-03-81  12:00a
	BAS18A   COM     14976 06-04-81  12:00a
	COMMENTS BAK      3560 06-05-81  12:00a
	FCOMP    COM      1408 04-13-81  12:00a
	DISKCOPY COM      1211 06-04-81  12:00a
	CONVERT  COM      3200 04-15-81  12:00a
	COMP     COM       256 04-15-81  12:00a
	KILO     BAS       768 04-23-81  12:00a
	20HAL    COM      1792 04-24-81  12:00a
	SPCWAR   BAS      5120 05-22-81  12:00a
	TTY      ASC      2432 05-22-81  12:00a
	VCOPY    BAT        26 04-24-81  12:00a
	SHIPS    MAC      1792 06-01-81  12:00a
	CIRCLE   MAC       384 06-01-81  12:00a
	RBAS     COM     32768 04-25-81  12:00a
	THREED   BAS      3072
	CUBE     DAT       402 04-30-81  12:00a
	       35 file(s)     144458 bytes
	                        8192 bytes free

The boot sector of the original PC-DOS 0.90 disk image contained the following bytes:

	00000000  eb 2f 14 00 00 00 60 00  20 37 2d 4d 61 79 2d 38  |./....`. 7-May-8|
	00000010  31 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |1...............|
	00000020  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
	00000030  00 fa 8c c8 8e d8 ba 00  00 8e d2 bc 00 7c fb a1  |.............|..|
	00000040  06 7c 8e d8 8e c0 ba 00  00 8b c2 cd 13 72 41 e8  |.|...........rA.|
	00000050  58 00 72 fb 2e 8b 0e 02  7c 51 bb 00 00 33 d2 b9  |X.r.....|Q...3..|
	00000060  08 00 be 01 00 56 b0 01  b4 02 cd 13 72 22 5e 58  |.....V......r"^X|
	00000070  e8 e7 00 2b c6 74 14 fe  c5 b1 01 be 08 00 3b c6  |...+.t........;.|
	00000080  73 04 8b f0 eb 01 96 56  50 eb dd 2e ff 2e 04 7c  |s......VP......||
	00000090  be 44 7d b8 42 7d 50 32  ff ac 24 7f 74 0b 56 b4  |.D}.B}P2..$.t.V.|
	000000a0  0e bb 07 00 cd 10 5e eb  f0 c3 bb 00 00 b9 04 00  |......^.........|
	000000b0  b8 01 02 cd 13 1e 72 34  8c c8 8e d8 bf 00 00 b9  |......r4........|
	000000c0  0b 00 26 80 0d 20 26 80  8d 20 00 20 47 e2 f3 bf  |..&.. &.. . G...|
	000000d0  00 00 be 76 7d b9 0b 00  fc f3 a6 75 0f bf 20 00  |...v}......u.. .|
	000000e0  be 82 7d b9 0b 00 f3 a6  75 02 1f c3 be f9 7c e8  |..}.....u.....|.|
	000000f0  a5 ff b4 00 cd 16 1f f9  c3 0d 0a 4e 6f 6e 2d 53  |...........Non-S|
	00000100  79 73 74 65 6d 20 64 69  73 6b 20 6f 72 20 64 69  |ystem disk or di|
	00000110  73 6b 20 65 72 72 6f f2  0d 0a 52 65 70 6c 61 63  |sk erro...Replac|
	00000120  65 20 61 6e 64 20 73 74  72 69 6b 65 20 61 6e 79  |e and strike any|
	00000130  20 6b 65 79 20 77 68 65  6e 20 72 65 61 64 f9 0d  | key when read..|
	00000140  0a 00 cd 18 0d 0a 44 69  73 6b 20 42 6f 6f 74 20  |......Disk Boot |
	00000150  66 61 69 6c 75 72 e5 0d  0a 00 50 52 8b c6 bf 00  |failur....PR....|
	00000160  02 f7 e7 03 d8 5a 58 c3  52 6f 62 65 72 74 20 4f  |.....ZX.Robert O|
	00000170  27 52 65 61 72 20 69 62  6d 62 69 6f 20 20 63 6f  |'Rear ibmbio  co|
	00000180  6d b0 69 62 6d 64 6f 73  20 20 63 6f 6d b0 c9 00  |m.ibmdos  com...|
	00000190  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
	000001a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
	000001b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
	000001c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
	000001d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
	000001e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
	000001f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|

Note that if you download the disk image from the PCjs website (using the "Save" button on a PCjs machine),
the following boot sector bytes will differ:

	00000000  eb 2f 14 00 00 00 60 00  20 37 2d 00 02 01 01 00  |./....`. 7-.....|
	00000010  02 40 00 40 01 fe 01 00  08 00 01 00 00 00 00 00  |.@.@............|

This is simply a side-effect of the [DiskDump](/modules/diskdump/) utility that's used to prepare disk images for the
PCjs website.  It automatically adds a BPB to the boot sector if the BPB is missing or incorrect, making it easier for
modern operating systems to mount the disk image.