Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/5/84; site rpics.UUCP Path: utzoo!watmath!clyde!burl!ulysses!gamma!epsilon!zeta!sabre!petrus!bellcore!decvax!mcnc!ncsu!uvacs!edison!steinmetz!rpics!weltyrp From: weltyrp@rpics.UUCP (Richard Welty) Newsgroups: net.lang.c Subject: Re: Re: This Sentence is False (DEC-20) Message-ID: <192@rpics.UUCP> Date: Wed, 2-Oct-85 22:07:20 EDT Article-I.D.: rpics.192 Posted: Wed Oct 2 22:07:20 1985 Date-Received: Sat, 5-Oct-85 08:18:23 EDT References: <1118@brl-tgr.ARPA> <139200010@uiucdcsb> <188@graffiti.UUCP> <314@ihdev.UUCP> <659@rtech.UUCP> Organization: RPI CS Department, Troy NY Lines: 27 > > On a Dec-20, you have a huge number of strange instructions, including : > ... > > skipn : skip never > > jumpn : jump never > > I always assumed these instructions 'existed' out of dedication to > orthogonality in the instruction set. The DEC 10/20 seemed to have > about a bizzilion instructions that boiled down to NOP. The advantage > was that it was easy to learn the mnemonics, since they were all > constructed in a regular fashion. It was also very easy to create and > examine object code: all the instructions are the same size, and the > scheme for modifying operand types is also very regular. Stanford had One more reason why they existed: When the PDP-6 was developed in the early sixties, DEC was a small company trying to compete in a big world. Allowing the massive number of nops was a way to keep the hardware small and simple, and thus fast and cheap -- it is harder not to have such instructions. -- Rich Welty (I am both a part-time grad student at RPI and a full-time employee of a local CAE firm, and opinions expressed herein have nothing to do with anything at all) CSNet: weltyrp@rpi ArpaNet: weltyrp.rpi@csnet-relay UUCP: seismo!rpics!weltyrp