Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: anton@mips.complang.tuwien.ac.at (Anton Ertl) Newsgroups: comp.arch Subject: Re: Why I've Dropped In Date: Sat, 14 Jun 2025 15:53:52 GMT Organization: Institut fuer Computersprachen, Technische Universitaet Wien Lines: 23 Message-ID: <2025Jun14.175352@mips.complang.tuwien.ac.at> References: <0c857b8347f07f3a0ca61c403d0a8711@www.novabbs.com> <102cd09$23hcu$1@dont-email.me> <42cac84be6fb35b9e468cc174919bc4a@www.novabbs.com> <102eske$2nqdn$1@dont-email.me> <697be23c211740763457a5f3b09df55d@www.novabbs.com> <102hfbb$3gg8b$1@dont-email.me> <97af35d9c1dc988bd7921bfecfef3d7b@www.novabbs.com> <102i2uh$3lm55$1@dont-email.me> <58e562def39603a1cd79da8751069588@www.novabbs.org> <102j3pg$qf8$1@dont-email.me> <2025Jun14.112604@mips.complang.tuwien.ac.at> Injection-Date: Sat, 14 Jun 2025 18:05:40 +0200 (CEST) Injection-Info: dont-email.me; posting-host="776ba7da7fe6b73acdb3f7225b5b828c"; logging-data="295300"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/YgWHdRWCBvf3lMurucGFj" Cancel-Lock: sha1:/QRL4wv09BCbtfIFPCc1Csmxj00= X-newsreader: xrn 10.11 anton@mips.complang.tuwien.ac.at (Anton Ertl) writes: >Stephen Fuld writes: >For the 8086 architecture, the effective addresses are reg, reg+const >or reg+reg (with severe restrictions on the registers usable for that; >the 8086 does not have GPRs). There is also absolute addressing on the 8086, and IA-32 (that encoding was repurposed for RIP-relative addressing on AMD64 IIRC). And I completely ignored the segment registers, which were intended to to provide a virtual-memory/relocation mechanism, but in MS-DOS programs were used as a cumbersome way to access more than 64KB of memory. Only in stuff like PC/IX was it used as intended AFAICT. The tragedy continued with the 80286, which now supported protected segments with up to 64KB, well suited for the kind of usage in PC/IX (but apparently that never had a 286 port) and actually used in Xenix, but which was against the grain for the kind of usage in MS-DOS. - anton -- 'Anyone trying for "industrial quality" ISA should avoid undefined behavior.' Mitch Alsup,