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Article #625489Re: different architecture, was PDP 11/40 system manual
From: John Levine
Date: Tue, 14 Aug 2018 23:42
Date: Tue, 14 Aug 2018 23:42
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2870 bytes
In article <pkvnqe$3ft$1...@gioia.aioe.org>, Rob Doyle <radi...@gmail.com> wrote: >> We all think it's obvious to have byte/word addressing where the word >> addresses are byte addresses with the low bits zero, but it wasn't >> obvious at all before IBM invented it for the 360. Once they had a >> memory architecture that could work either way, building the >> instruction set wasn't so hard. > >... and forgotten by the time that the DEC Alpha arrived on the scene. > >The first few versions of the DEC Alpha couldn't load or store 8-bit or >16-bit data to/from memory. Those instructions were added (EV5) when >they realized how crazy that decision was. Oops. The IBM 801 did the same thing. The theory on the 801 was that they would really do a RISC and strip everything out of the hardware that they could do in software. At the time the logic to do byte stores to word memory was complex enough that they figured (probably correctly because they had better compiler people than anyone else) that they could do it in software and make the machine faster over all. As gates continued to get cheaper a lot of stuff has crept back in, with misaligned and partial word loads and stores near the head of the line. -- Regards, John Levine, jo...@iecc.com, Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. https://jl.ly
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X-Received: by 2002:a24:43cb:: with SMTP id s194-v6mr9613335itb.3.1534290160594; Tue, 14 Aug 2018 16:42:40 -0700 (PDT) X-BeenThere: alt.folklore.computers@googlegroups.com Received: by 2002:a24:ba19:: with SMTP id p25-v6ls99099itf.8.canary-gmail; Tue, 14 Aug 2018 16:42:39 -0700 (PDT) X-Received: by 2002:a24:294d:: with SMTP id p74-v6mr9540239itp.36.1534290159810; Tue, 14 Aug 2018 16:42:39 -0700 (PDT) MIME-Version: 1.0 Path: mbox-mo1.pugleaf.net!g5-v6ni1342iti.0!nntp.google.com!border1.nntp.dca1.giganews.com!border2.nntp.dca1.giganews.com!nntp.giganews.com!news.iecc.com!.POSTED.news.iecc.com!not-for-mail From: John Levine <jo...@taugh.com> Newsgroups: alt.folklore.computers Subject: Re: different architecture, was PDP 11/40 system manual Date: Tue, 14 Aug 2018 23:42:39 -0000 (UTC) Organization: Taughannock Networks Message-ID: <pkvpdf$gb3$1@gal.iecc.com> References: <21aaeee8-c41a-4442-a4eb-ea6a29b1e4f1@googlegroups.com> <5b71ce88.4681852@news.dslextreme.com> <pksssc$2p6c$1@gal.iecc.com> <pkvnqe$3ft$1@gioia.aioe.org> Injection-Date: Tue, 14 Aug 2018 23:42:39 -0000 (UTC) Injection-Info: gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970"; logging-data="16739"; mail-complaints-to="ab...@iecc.com" Cleverness: some X-Newsreader: trn 4.0-test77 (Sep 1, 2010) Originator: jo...@iecc.com (John Levine) Bytes: 2316 Lines: 28 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit