227 lines
14 KiB
HTML
227 lines
14 KiB
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<TITLE>Int 2F/AX=5500h
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<META NAME="Description" CONTENT="
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Int 2F/AX=5500h - DOS 5+ - COMMAND.COM INTERFACE -
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AX = 5500h
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Return: AX = 0000h if an instance of COMMAND.COM is already running
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DS:SI - entry point table
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Notes: used to access the shareable portion of COMMAND.COM, which may have
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been moved into the HMA; only the primary COMMAND.COM retains this
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portion
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procedures called from a dispatcher in COMMAND's resident portion;
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most assume that the segment address of the resident portion is on
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the stack and are thus not of general use
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DR PalmDOS up to DR-DOS 7.03 COMMAND.COM do not support this call.
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">
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<h2>Int 2F/AX=5500h
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<td><a href="int.htm" tppabs="http://www.ctyme.com/intr/int.htm">Interrups</a></td>
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<td><a href="cat.htm" tppabs="http://www.ctyme.com/intr/cat.htm">Categories</a></td>
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<td><a href="alpha.htm" tppabs="http://www.ctyme.com/intr/alpha.htm">Contents</a></td>
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<p><img src="rbline.gif" tppabs="http://graphics.ctyme.com/gif/rbline.gif" width="100%" alt="------"><p>
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<h3><font color=#C00040>DOS 5+ - COMMAND.COM INTERFACE</font></h3>
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<PRE>
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AX = 5500h<br>
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<p><b>Return:</b><br>AX = 0000h if an instance of COMMAND.COM is already running
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DS:SI -> entry point table
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</PRE>
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<p><b>Notes:</b>
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Used to access the shareable portion of COMMAND.COM, which may have
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been moved into the HMA; only the primary COMMAND.COM retains this
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portion.
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Procedures called from a dispatcher in COMMAND's resident portion;
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most assume that the segment address of the resident portion is on
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the stack and are thus not of general use.
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DR PalmDOS up to DR-DOS 7.03 COMMAND.COM do not support this call..
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When loading the default command processor (no SHELL= directive in
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CONFIG.SYS), MS-DOS 6.0-6.22 IO.SYS & PC DOS 6.1-2000 IBMBIO.COM
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check a signature <a href="rb-4286.htm#Table4099" tppabs="http://www.ctyme.com/intr/rb-4286.htm#Table4099">(see #04099)</a> in the COMMAND.COM file image to test
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if it is actually their own shell and has the correct version, before
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they will launch it. If the signature is not found, the message
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"Invalid COMMAND.COM" will be displayed. This test seems to have
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vanished with MS-DOS 7+, as it uses an .EXE style file format..
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In addition to this, the MS-DOS/PC DOS COMMAND.COM checks the version
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of the underlaying OS to see if it is their own. Hence, the
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PC DOS 6.1 (and by SETVER version faking also the PC DOS 7 and 2000)
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COMMAND.COM also run on Novell DOS 7 - DR DOS 7.03, which all
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identify themselves as DOS API level 6.0 and IBM OEM (not yet tested
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as primary shell). PC DOS 5.0 COMMAND.COM should run on DR PalmDOS
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(untested)..
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The MS-DOS 7+ COMMAND.COM seems to no longer perform this kind of
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version check any more, which can cause a serious deadlock situation
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on a multi-boot system with DR-DOS installed, when the MS-DOS 7+
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COMMAND.COM is placed in C:\. When IBMBIO.COM attempts to load the
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MS-DOS 7+ COMMAND.COM as a primary shell under DR-OpenDOS 7.02 to
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DR-DOS 7.03 no error message will be displayed by COMMAND.COM, but
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the machine will just hang. To defuse this situation, DR-DOS 7.02+
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IBMBIO.COM was changed to still scan for a SHELL= directive in
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[D]CONFIG.SYS even in F5-mode. For maximum safety, the MS-DOS 7
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COMMAND.COM should be moved from C:\ to C:\WINDOWS\COMMAND\
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and a DCONFIG.SYS file should be created containing for example
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SHELL=C:\DRDOS\COMMAND.COM instead. If a MS-DOS CONFIG.SYS file
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exists, it should contain a SHELL=C:\WINDOWS\COMMAND\COMMAND.COM
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directive. (If no shell can be found at all, DR-DOS IBMBIO.COM would
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display a prompt to enter the proper path to COMMAND.COM)..
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The DR-OpenDOS 7.02+ COMMAND.COM is designed to also run on 3rd party
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operating systems like MS-DOS/PC DOS 3.31+, Windows 9x, and in DOS
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boxes of OS/2, Windows NT and 2000, and will for example also take
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advantage of long filenames.
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<p><b>See Also:</b>
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<a href="rb-4897.htm" tppabs="http://www.ctyme.com/intr/rb-4897.htm">AX=5501h</a>
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<PRE>
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<p>
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Format of Microsoft COMMAND.COM file image signature:
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<a name=table4100></a>
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Offset Size Description (Table 04100)
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00h 3 BYTEs E9h xxh xxh (JMP instruction)
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03h BYTE version
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<p><b>bits 7-4:</b><br>Major version
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<p><b>bits 3-0:</b><br>Minor version code
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( 60h for MS-DOS 6.0 and PC-DOS 6.1;
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64h for MS-DOS 6.20, Japanese MS-DOS 6.2, Hangeul MS-DOS 6.2;
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66h for MS-DOS 6.22, PRC (Chinese) MS-DOS 6.22;
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70h for PC DOS 7, PC DOS 7 Y2K edition )
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</PRE>
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<p><b>Notes:</b>
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Since DR DOS 6.0+, MS-DOS 7.0+, PTS-DOS, S/DOS, 4DOS/NDOS use an .EXE
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style shell file format, this signature is not met by any release of
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these shells. DR DOS 3.31-5.0 used a different jump (E8h) at offset
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00h..
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Older releases of MS-DOS/PC DOS all had a jump (E9h) at offset 00h, but
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other values at offset 03h. For reference here is a list of the
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values for some of these older shells:
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00h for PC DOS 1.10, Olivetti DOS 2.11, MS-DOS 5.0,
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Russian MS-DOS 5.0
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1Eh for MS-DOS 4.01
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BAh for PC DOS 3.10, 3.20, MS-DOS 3.30
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<p>
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<b>Category: <a href="cat-039.htm" tppabs="http://www.ctyme.com/intr/cat-039.htm">
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Shells/Command Interpreters</a>
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- <a href="int-2f-1.htm" tppabs="http://www.ctyme.com/intr/int-2F.htm">
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Int 2Fh</a>
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D</a>
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<td><a href="alpha.htm" tppabs="http://www.ctyme.com/intr/alpha.htm">Contents</a></td>
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