Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site peora.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!harvard!talcott!panda!genrad!decvax!tektronix!uw-beaver!cornell!vax135!petsd!peora!joel From: joel@peora.UUCP (Joel Upchurch) Newsgroups: net.arch Subject: Re: RISC and MIPS Message-ID: <1432@peora.UUCP> Date: Mon, 5-Aug-85 09:05:31 EDT Article-I.D.: peora.1432 Posted: Mon Aug 5 09:05:31 1985 Date-Received: Sat, 10-Aug-85 23:39:17 EDT References: <419@kontron.UUCP> <237@weitek.UUCP> <437@petrus.UUCP> Organization: Perkin-Elmer SDC, Orlando, Fl. Lines: 15 >A side note: The Berkeley RISC's have no absolute addressing mode, >they fake it by using R0 (always 0) plus an offset. BUT, the offset >can only be 13 bits, hence they can only absolutely address the first >2**13 locations in memory. Large programs, eg the UNIX kernel >(particularly from Berkeley) use much more than 2**13 (like 2**19) for >instructions, hence the problem is how well would a RISC do when it >takes 2 instructions to form an absolute address and probably requires >a register? I'll accept RISCs when I see one runnning 4.3 BSD faster >than an 11/780. I would like to point out that the IBM 370 (usually considered a CISC :-> ) doesn't have absolute addressing and that it only has a displacement of 2**12 bytes. They seem to be able to get some rather large operating systems, including UNIX, to run on it.