MZ is back!

README.md

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 <img width="150" height="150" align="left" style="float: left; margin: 0 10px 0 0;" alt="MS-DOS logo" src="https://github.com/Microsoft/MS-DOS/blob/main/.readmes/msdos-logo.png">   
 
-# MS-DOS v1.25 and v2.0 Source Code
+# MS-DOS v1.25, v2.0, v4.0 Source Code
 
-This repo contains the original source-code and compiled binaries for MS-DOS v1.25 and MS-DOS v2.0.
+This repo contains the original source-code and compiled binaries for MS-DOS v1.25 and MS-DOS v2.0, plus the source-code for MS-DOS v4.00 jointly developed by IBM and
+Microsoft.
 
-These are the same files [originally shared at the Computer History Museum on March 25th, 2014]( http://www.computerhistory.org/atchm/microsoft-ms-dos-early-source-code/) and are being (re)published in this repo to make them easier to find, reference-to in external writing and works, and to allow exploration and experimentation for those interested in early PC Operating Systems.  
+The MS-DOS v1.25 and v2.0 files [were originally shared at the Computer History Museum on March 25th, 2014]( http://www.computerhistory.org/atchm/microsoft-ms-dos-early-source-code/) and are being (re)published in this repo to make them easier to find, reference-to in external writing and works, and to allow exploration and experimentation for those interested in early PC Operating Systems.  
 
 # License
 

v4.0-ozzie/bin/DISK1/AUTOEXEC.BAT

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+date
+time
+prompt $p$g
+path a:\bin;a:\
+

v4.0-ozzie/bin/DISK1/BIN/DEMO1.BAT

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+cd bin
+pound 290 a:bbset.exe a:sm.exe
+

v4.0-ozzie/bin/DISK1/BIN/DEMO2.BAT

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+c:
+cd \bin
+pound 800 bbset.exe sm.exe
+

v4.0-ozzie/bin/DISK1/BIN/DEMO3.BAT

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+c:
+cd \bin
+cd a:\bin
+detach pound 800 bbset.exe sm.exe
+detach pound 290 a:bbset.exe a:sm.exe
+basica a:prime
+

v4.0-ozzie/bin/DISK1/COMMANDS.DOC

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+
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+
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+
+                                Multi-Tasking MS-DOS
+                               Beta Test Release 1.00
+
+                                   Command Guide
+
+
+            ARENA.EXE - Prints out arena assignments
+
+                 arena
+
+                      The system's  memory arena  is printed  out.   The
+                      number listed  under the owner field is the PID of
+                      the process which owns the memory.
+
+
+            BBSET.EXE - Set and report on behavior bits
+
+                 bbset [-o] [ {+|-}bitname ... ] fname ...
+
+                      BBSET sets or clears behavior bits in an .EXE file
+                      header.   Multi-Tasking MS-DOS  uses the  behavior
+                      bits   to   determine   the   level   of   special
+                      compatibility   support    needed   to   run   the
+                      application.
+
+                      BBSET will  set  (if  +bitname)  or  clear  (if  -
+                      bitname)  the   named  behavior  bit(s)  from  the
+                      specified files.   If  the -o switch is specified,
+                      BBSET writes  a report  on the  current setting of
+                      all the  defined behavior  bits  to  stdout  after
+                      making the requested changes.
+
+                      For a  list of  behavior  bits  that  BBSET  knows
+                      about, type BBSET without any arguments.
+
+
+            COUNTDOW.EXE - Count down a CPU loop
+
+                 countdown number
+
+                      Its argument  is a  number; it  counts the  number
+                      down to 0, at about a 1hz rate.     It  prints out
+                      the countdown.   Another  CPU  loop  program  like
+                      TEXT, but  this  one  terminates  when  the  count
+                      reaches 0
+
+
+            DETACH.EXE - Detaches a child process
+
+                 detach command [argument ...]
+
+                      The command  given is run as a background process.
+                      Detach prints  out the  Command Subgroup ID (CSID)
+                      which may  be used  as  an  argument  to  KILL  to
+                      terminate the process.
+
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+
+     Multi-Tasking MS-DOS Command Guide - Page: 2
+
+            HE_DAEM.EXE - Hard error catcher
+
+                 detach he_daem
+
+                      Intercepts hard  errors, reports them and requests
+                      user action.   This  should always  be run  in the
+                      background for now.  Put the above command line in
+                      your AUTOEXEC.BAT  file if you're not going to use
+                      the Session Manager (SM).
+
+
+            KILL.EXE - send a signal to a process
+
+                 kill [-nn] [sig=nn] [disp=mm] pid ...
+
+                      Sends signal  nn with  disposition mm to processes
+                      mentioned in pid.  Defaults to SIGTERM and process
+                      tree disposition.
+
+
+            POUND.EXE - Exercise disk I/O system
+
+                 pound [t]count filea fileb
+
+                      Pound reads  sequencially through filea and fileb,
+                      reading 512  bytes at  a time  alternating between
+                      the files  on each  read.  When the end of file is
+                      read the  following read  for that  file begins at
+                      the  beginning  of  the  file.    If  a  count  is
+                      specified without  the preceeding  "t" then  pound
+                      reads 512  bytes, count  number of times from each
+                      file  before  the  program  terminates.    If  "t"
+                      preceeds the  count value  then the files are read
+                      for count  number of  seconds before  the  program
+                      terminates.
+
+
+            SLEEP.EXE - Sleep for a while
+
+                 sleep sec[.millisec]
+
+                      Sleep will  execute a  sleep system  call for  the
+                      number  of  seconds  and  milliseconds  specified.
+                      This might  be useful  in batch files to pause for
+                      an interval  as opposed  to  waiting  for  a  user
+                      response.
+
+
+            SM.EXE - Session manager
+
+                 sm
+
+                      Manages multiple  processes running  on  different
+                      screens.   Uses initialization  file SM.INI.  This
+
+
+
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+
+
+     Multi-Tasking MS-DOS Command Guide - Page: 3
+
+                      program includes  the hard error catcher, so don't
+                      run HE_DAEM  if you're going to use this.  See the
+                      file SM.DOC for more information.
+
+
+            TEXT.EXE - Loop and print text
+
+                 text argument
+
+                      CPU loops  and prints  its argument  every  2  CPU
+                      seconds or so
+
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v4.0-ozzie/bin/DISK1/CONFIG.SYS

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+buffers = 40
+files = 20
+break=on

v4.0-ozzie/bin/DISK1/README

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+
+
+
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+
+
+                                Multi-Taking MS-DOS
+                               Beta Test Release 1.00
+
+                                   Release Notes
+
+
+                 Enclosed you  will find  Microsoft's first beta release
+            of Multi-tasking  MS-DOS.  This version is based upon MS-DOS
+            Version 2  sources, we  will be  reimplementing  the  multi-
+            tasking enhancements on top of Version 3 sources shortly.
+
+                 Although we  have distributed  a bootable  disk for the
+            IBM PC,  this package  can be adapted to any MS-DOS machine.
+            Those manufacturers  who are  designing IBM compatible ROMs,
+            would be  wise to keep multi-tasking in mind.  Specifically,
+            this IBM  PC implementation  has had  to hook out the entire
+            disk (both  floppy and  hard disk) ROM code because after he
+            IBM code  set's up  the DMA  transfer it simply loops in ROM
+            waiting for the interrupt to occur (routine WAIT_INT).
+
+            Problems you may wish to avoid within future ROMs are:
+                 1)   loading ES  with the  physical video  RAM location
+                      (label M3)
+                 2)   Looping in ROM on Cntrl-NumLock (label K40)
+                 3)   No  way  to  add  special  detecting  special  key
+                      strokes which  a jump  out into  RAM after reading
+                      the keystroke at KB_INT would avoid
+                 4)   Not being  able to hook the loading of DS to point
+                      to DATA (EQU 40H) in numerous routines.
+            Other than  these deficiencies the ROM code developed should
+            be very usable.
+
+                 By implementing the above suggestions, the size of your
+            BIOS can  be reduced  since it  will  not  be  necessary  to
+            duplicate functionality in RAM.
+
+                 More  detailed  specifications  of  the  device  driver
+            formats will  be forth  coming.  For the time being you will
+            have to  make use  of the sample source code for the IBM PC.
+            If you  have further  questions please contact Microsoft OEM
+            customer support through Technical Assist Requests (TAR).
+
+
+               * * *  WARNING  * * *  WARNING  * * *  WARNING  * * *
+
+                 Each copy  of this  software distribution has been
+                 individually serialized  to facilitate  tracing of
+                 unauthorized duplication.
+
+               * * *  WARNING  * * *  WARNING  * * *  WARNING  * * *
+
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