Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
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Path: utzoo!linus!decvax!microsoft!markz
From: markz@microsoft.UUCP (Mark Zbiokowski)
Newsgroups: net.micro.pc
Subject: re: DOS 2.0 info needed
Message-ID: <8659@microsoft.UUCP>
Date: Sun, 9-Oct-83 18:53:54 EDT
Article-I.D.: microsof.8659
Posted: Sun Oct  9 18:53:54 1983
Date-Received: Mon, 10-Oct-83 10:37:00 EDT
Organization: Microsoft Corporation
Lines: 14


	How does COMMAND.COM tell DOS where the handler for the
	EXEC function is?

On non-IBM systems, the EXEC system call is part of the kernel.  On IBM
systems COMMAND.COM installs a handler for INT 21h and filters those
calls with AH == 4Bh.

	How is it possible that the word at offset 6 in the program
	segment prefix is both part of a long call and the size
	of a the segment?

Clever manipulation: any CS:IP that refers to a particular location
has 12 bits of redundant information on the 8088/6.  Shuffling this
information around gives the desired result.