Re: [問題] dos為何要有記憶體配置的中斷指令?
http://www.ctyme.com/intr/rb-2980.htm
DOS 2+ internal - SET CURRENT PROCESS ID (SET PSP ADDRESS)
AH = 50h
BX = segment of PSP for new process
Notes: DOS uses the current PSP address to determine which processes own
files and memory; it corresponds to process identifiers used by other OSs.
Under DOS 2.x, this function cannot be invoked inside an INT 28h handler
without setting the Critical Error flag. Under MS-DOS 3.0+ and DR DOS 3.41+,
this function does not use any of the DOS-internal stacks and may thus be
called at any time, even during another INT 21h call. Some Microsoft
applications such as Quick C 2.51 use segments of 0000h and FFFFh and direct
access to the SDA (see #01687 at AX=5D06h) to test whether they are running
under MS-DOS rather than a compatible OS; although one should only call this
function with valid PSP addresses, any program hooking it should be prepared
to handle invalid addresses. This function is supported by the OS/2
compatibility box. This call was undocumented prior to the release of DOS 5.0
See Also: AH=26h - AH=51h - AH=62h
Category: DOS Kernel - Int 21h - D
※ 引述《tester.bbs@bbs.csie.ncu.edu.tw (try or test)》之銘言：
: > DOS 只是沒有 UNIX 的多工，可以視為循序執行的單工環境，
: > （把自己串到 Interrupt Vector 的 TSR 不討論）
: > 但是仍然有父子行程的概念
: > 另外，如果去讀 PC DOS 7.0 使用手冊，
: DOS 7.0 跟 win95 已經是同一種版本了, 從 win3.1 之後開了多個視窗
: 同時跑(至少是交錯地跑), 要算那一種系統 ?
: DOS 過了 286 protection Mode 的時代進入 VM386, 只要是用了 MMU 功
: 能且使用1MB 以上高位址記憶體執行程式, 就進入 win32 .
: 使用了 protection mode 執行程式(不是只拿 1MB 之後當 ram disk 用,
: 再用 pseudo reset 切回 real mode 跑程式), 不想用多工都不行, 那個
: VM386 mode 是硬體多工.
: > 系統呼叫 功能
: > 00H Terminating a program
: > 31H Terminating a program with a specified portion remaining in memory
: > 4CH Terminating a program and passing control to the calling process
: > 4DH Determining how a process ended
: > 這代表 DOS 是有 Process 概念的...
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