Notes Concerning the
June, 1981 Pre-Release Copy
of IBM® Personal Computer™ DOS 1.00
(Also referred to as: "IBM PC DOS 0.90"; see below)

Web Presentation and Text are Copyright©2017, 2019, 2021 by Daniel B. Sedory
NOT to be reproduced in any form without Permission of the Author !




The History of this Pre-Release Image File


How to Obtain a Copy for Your Own Research


Some Comments from Dick Conklin on the Disk's Contents


The Comments File on the Diskette

Notes about this diskette    6/5/81
1. The autoexec facility has been fixed, and works on this system.
2. The system files1 have reverted to upper case letters again, but will not be included in any
 directory searches because of a new byte (attribute2) in the directory entry (they won't show on a DIR
 command, and can't be erased, copied, folded, spindled or mutilated). The FORMAT ans SYS commands both
 can be used to put these files on a diskette3 (if SYS is used, the disk must have already had the system
 on it4). In addition, FORMAT writes the boot record5 and copies COMMAND.COM6.

 2 Only the System bit was set at this time (attribute byte = 0x04); when released, these files had both System
   and Hidden attributes set (attribute byte = 0x06). This is the 12th byte in each Directory entry.
 3 See our comments further below on the FORMAT and SYS commands. 
 4 So why was SYS.COM created, when it appears to have very little use? SEE NOTES BELOW for the answer!
 5 By copying the Boot Record from Sector 0 of boot diskette; not by writing a new one from within the FORMAT.COM
   file itself as the later (release) FORMAT program does!
 6 In addition to IBMBIO.COM and IBMDOS.COM, _when_ its '/S' switch is used.

3. The system now contains single-drive support that makes the dip switch settings very important. The DOS
   now conforms with the proper dip switch settings for number of drives namely -
   7 on, 8 on - 1 drive
   7 off, 8 on - 2 drives
   7 on, 8 off - 3 drives
   7 off, 8 off - 4 drives
4. The disk contains some extra programs, as follows -
   vcopy - used like the copy command - it's a batch file that invokes copy, then invokes a file compare
   program [FCOMP.COM] to verify the copied file is the same as the original.
   mode  - changes the mode of the screen or line printer
          the command has two basic options
         OPTION 1 (line printer) ex: MODE LPT1:132,8

         lpt<#> - specify printer number 1-3 , usually 1
	 m - 80 , 132 characters per line

	 n - 6 , 8 specifies 6 or 8 lines per inch

         OPTION 2 (display) ex: MODE 80,r

	 m - 40 , 80 characters per line

	 n - r , l shifts the screen to the right or left (repeated use of this option allowed)
diskcopy -
        'DISKCOPY dr1 dr2" where dr1 will contain the source diskette, and dr2 will contain the target.
           If only the first dr is specified, the default dr will be used for dr2 - if both dr's are
           omitted, a single drive copy will be done on the default dr.
    comp - diskette compare, compares all 40 tracks of 2 diskettes (use after fcopy7 if you suspect a problem.

    7 But there is no 'fcopy' on the diskette; must have meant diskcopy (was there ever an early;
      as in early 1981 or earlier, FCOPY program - possibly a beta version, or from SCP?).
    fcomp - file compare program - compares 2 files on the same or different drives, indicates up to 10
           offsets that don't compare. To invoke, enter "FCOMP fn1 fn2". Both filenames may include drive specifiers
           and both are optional (the program prompts). Note that compares of non-text files (such as .COM
           files) will cause a message indicating no eof was found. This is normal for such files, and does not
           indicate an error - the program looks for an eof mark (1AH), which is present in source files,
           but not in .COM files.
    convert - To date, 3 different formats of diskette maps have been used by DOS. The first contained the
           dir on track 2 and was the system that did not prompt for tha date. The second was the system
           with the dir on track 2 and did prompt for the date - it was a conversion system to be used
           for converting diskettes with the first format to the new format directory. The latest system,
           (4/15/81 or later) contains another change - the dir has now been moved to track 0, and both
           previous formats are incompatible. If your diskettes are in the second format, use the FORMAT
           command on this disk to format a new disk, then enter "CONVERT". It copies all files
           from a diskette that has the second (date in dir, dir on trk 2) to the new formatted diskette.
           (Sorry, there's no program to go from the oldest to the newest format).

Figure 3. This is a marked-up and combined screens picture of a Norton Disk Editor view of the Directory after EDLIN was used to only view the COMMENTS file; not make any changes.

If you do so; without making another edit change, then EDLIN erases its 'back-up' file (COMMENTS.BAK) as shown within the GREEN circle.

Notice how Norton's Disk Editor considers all 3 files (in RED) as having errors because there are only zero bits in their 'Date bytes'. The disk's COMMAND.COM program simply ignores these and doesn't display anything for them.

Note: Never attempt to open a 'FAT object' in Norton Disk Editor while Windows is running, it will always CRASH the program!


Use of the FORMAT and SYS Commands


Early DIR Command, AUTOEXEC.BAT and BASIC's FILES Command


Detailed Locations of Every File on the Disk


The actual screen display of this version's DIR command has no 'Time Column' nor are file names listed in the same order found in the Directory (compare to our manually compiled listing at right):

Figure 6. The 3 files with no listed date had zero bits in their 'date bytes'; the DIR command of this version's COMMAND.COM displays no date when encountering that 'technical error' (there cannot be a zero-th month or day, but all zero bits for the year does mean 1980).

 Absolute Sector 3
 -----------------                        Absolute
   Name   .Ext    Size    Date    Cluster Sector(s)  A R S H D V

  IBMBIO   COM    2560   5-29-81      2     7-11     - - S - - -
  IBMDOS   COM    5566   5-29-81      7    12-22     - - S - - -
  COMMAND  COM    2576   5-29-81     18    23-28
  DEBUG    COM    5450   5-27-81     24    29-39
  TIME     COM     243   5-19-81     35      40
  DATE     COM     245   5-20-81     36      41
  ASM      COM    6389   5-15-81     37    42-54
  FORMAT   COM    2048   5-29-81     50    55-58
  HEX2BIN  COM     483   5-07-81     54      59
  CHKDSK   COM    1224   5-30-81     55    60-62
  BASIC    COM   11008   6-04-81     58      63    <- Fragmented
                                     66    71-90
                                    184     189
  EDLIN    COM    2231   5-29-81     59    64-68
  COMMENTS        3561   6-05-81     64    69-70   <- Fragmented
                                    112   117-121
  MOVBAS   COM     128   4-23-81     86      91
  BAS18    COM   11008   6-04-81     87    92-112  <- Fragmented
                                    127     132

 Absolute Sector 4
  BASICA   COM   14976   6-04-81    108     113    <- Fragmented
                                    134   139-164
                                    185   190-192
  AUTOEXEC BAT      24    NONE*     109     114
  SYS      COM     896   6-03-81    110   115-116
  DISKCOPY COM    1211   6-04-81    117   122-124
  COMMENTS BAK    3560   6-05-81    120   125-131
  BAS18A   COM   14976   6-04-81    128   133-138  <- Fragmented
                                    160   165-188
  FCOMP    COM    1408   4-13-81    188   193-195
  KILO     BAS     768   4-23-81    191   196-197
  SPCWAR   BAS    5120   5-22-91    193     198    <- Fragmented
                                    202   207-208
                                    208   213-217
                                    215     220
                                    222     227
  CONVERT  COM    3200   4-15-81    194   199-205
  COMP     COM     256   4-15-81    201     206
  20HAL    COM    1792   4-24-81    204   209-212
  MODE     COM     675    NONE*     213   218-219
  TTY      ASC    2432   5-22-81    216   221-225
  VCOPY    BAT      26   4-24-81    221     226
  THREED   BAS    3072    NONE*     223   228-232  <- Fragmented
                                    297     302
  SHIPS    MAC    1792   6-01-81    228   233-236
  CIRCLE   MAC     384   6-01-81    232     237

 Absolute Sector 5
  RBAS     COM   32768   4-25-81    233   238-301
  CUBE     DAT     402   4-30-81    298     303

 * The "NONE" entries mean no Date had been entered into
   the OS when these files were added; the Date bits in
   each of these file Directory entries were all zeros.
   Later versions would use a 'default date' of 1-1-80.

                                         Clusters   Sectors
  Unused clusters/sectors on diskette:    299-314   304-319
  Unused sectors at end of diskette = 16
 (16 sectors x 512 bytes/sector = 8,192 bytes free space).


Examples of Data Found in Slack Space


Download All the Slack Space Data


How to Use ASM.COM on this Disk





1[Return to Text]  Both files are exactly 6,389 bytes, and only 5 bytes differ. The affected instructions are:

It's clear the Stack Pointer was moved from 0x2037 to 0x2085 for these and a few instructions which depend on that location. Yet there appears to be no mention of this in the Source Code for version 2.44; where we only find:

Perhaps this change in 2.24 was considered too minor to mention.

2[Return to Text]  The Assembly Source Code for ASM.COM (Version 2.44), as well as much of the source code for IBM PC DOS 2.0, has been publicly available for research purposes since March 25, 2014 (see this article by Len Shustek at CHM). In that file, you'll find:

Which leads us to believe this bit of slack space is from around the beginning of March, 1981.

3[Return to Text]  This pre-release version of FORMAT.COM contains a unique oddity you won't find anywhere else in DOS. Its author, Bob O'Rear, for some reason decided to insert his name in the program in a way which would require more than a glance to notice. The final release verison did not include any of this (although his name is found there as well, because FORMAT.COM was revised to include a copy of the DOS 1.00 Boot Sector, which Bob had already inserted his name into!):

Those color highlighted bytes above, are nothing more than:


First Published: 10 JUN 2017 (10.06.2017).
Updated: 10 JUN 2017 (10.06.2017); 16 JUN 2017 (16.06.2017); 18 JUN 2017 (18.06.2017); 19 JUN 2017 (19.06.2017); 21 JUN 2017 (21.06.2017); 22 JUN 2017 (22.06.2017); 25 JUN 2017 (25.06.2017); 1 JUL 2017 (01.07.2017); 26 FEB 2018 (26.02.2018); 22 JUL 2019 (22.07.2019) - added picture of diskette Dick Conklin sent us and comments on how it still boots-up! 28 SEP 2020 (28.09.2020) - added notes on CP/M function calls in this version of ASM.COM.
Last Update: 9 FEB 2021 (09.02.2021) -
Corrected MD5 Checksum, made some clarifications.

You can write to us using this: email address (opens in a new window).

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