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From: John Levine <johnl@taugh.com>
Newsgroups: comp.arch
Subject: Re: Why VAX Was the Ultimate CISC and Not RISC
Date: Sun, 2 Mar 2025 20:02:03 -0000 (UTC)
Organization: Taughannock Networks
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According to Anton Ertl <anton@mips.complang.tuwien.ac.at>:
>>That's not a fair comparison. VAX design started in 1975 and shipped in 1978.
>>The first ARM design started in 1983 with working silicon in 1985. It was a
>>decade later.
>
>The point is that ARM outperformed VAX without using caches.  DRAM
>with 800ns cycle time was available in 1971 (the Nova 800 used it).
>By 1977, when the VAX 11/780 was released, certainly faster DRAM was
>available.

Oh, OK.  How was the code density?  I know ARM was pretty good but VAX
was fantastic since they sacrified everything else to compact instructions.
The pages were only 512B, they really thought memory was expensive even
though the trend lines were clear.

>IBM tried to commercialize it in the ROMP in the IBM RT PC; ...
>... The delay between the
>completion of the ROMP design, and introduction of the RT PC was
>caused by overly ambitious software plans for the RT PC and its
>operating system (OS)." 

I was there, designing AIX. IBM couldn't decide what they wanted, and
they didn't understand Unix, but they wanted it yesterday, so they had
an elaborate and slow "virtual resource manager" with the operating
systems running on top. It turned out that the only operating system
was AIX, with the VRM just extra overhead. We wasted a lot of time
explaining why we weren't going to do random IBM stuff of which the
most memorable was user labels in the inodes (well, OS DASD has them.)

It did not help that I naively believed their initial schedule so we
based AIX on 4.1BSD rather than the recently released 4.2 and it
didn't have dynamic shared libraries and other 4.2 stuff. Someone else
did a 4.2 port that ran way faster than AIX did.

-- 
Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly