Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!decwrl!labrea!glacier!jbn
From: jbn@glacier.STANFORD.EDU (John B. Nagle)
Newsgroups: comp.sys.mac
Subject: Re: MAC 88000
Keywords: IBM 360 1401
Message-ID: <17573@glacier.STANFORD.EDU>
Date: 20 Jul 88 04:53:01 GMT
References: <261@hodge.UUCP> <370STORKEL@RICE> <607@riddle.UUCP> <441@softway.oz>
Reply-To: jbn@glacier.UUCP (John B. Nagle)
Organization: Stanford University
Lines: 30

In article <441@softway.oz> chris@softway.oz (Chris Maltby) writes:
>Roll on IBM - I want to standardise on the 360
>(actually 1401) architecture - its RISC and CISC together!

     When IBM came out with the PC/RT, ballyhooing their "reduced instruction
set machine", I observed that the PC/RT instruction set was larger than that
of the IBM System/360.  This was a bit amusing.

     Incidentally, the architecture of the IBM 1401, a popular business
computer of the early 1960s, was totally different from that of the System/360.
The IBM 1401 was a variable-number-length machine with decimal arithmetic.
Each character of memory held 6 bits.  Memory addresses were decimal.
The IBM System/360 was the first machine with what we today consider standard
computer architecture: byte-addressable memory (the word "byte" was coined
at IBM and first appeared outside IBM in the System/360 product announcement.),
32-bit words, 16-bit halfwords, 64-bit longwords, 8-bit characters, and
a 16-megabyte address space potentially expandable to 2^32 bytes.
It represented a clean break with IBM's two previous product lines; the
business machines, with decimal arithmetic and memory, and the scientific
machines, the 701-704-709-7040-7090-7094 line, with 36-bit words,
binary arithmetic, and a 64K word address space.

     IBM 1401 emulation hardware was available for the smaller System/360 
machines as an option, but this was not part of the 360 architecture.

     Sorry for the digression, but I wanted to set the record straight.
The IBM System/360 was a major breakthrough, and the hardware architecture
was excellent.  (The same cannot be said for the software architecture;
design mistakes made in OS/360 still haunt us.)

					John Nagle