Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!mcsun!ukc!cam-cl!news
From: cet1@cl.cam.ac.uk (C.E. Thompson)
Newsgroups: comp.arch
Subject: Re: Can old architectures run fast?
Message-ID: <1991May9.214959.22599@cl.cam.ac.uk>
Date: 9 May 91 21:49:59 GMT
References: <8283@uceng.UC.EDU> <7628@auspex.auspex.com> <8324@uceng.UC.EDU> <1991May05.174756.9026@iecc.cambridge.ma.us>
Reply-To: cet1@cl.cam.ac.uk (C.E. Thompson)
Organization: U of Cambridge Comp Lab, UK
Lines: 16

In article <1991May05.174756.9026@iecc.cambridge.ma.us> johnl@iecc.cambridge.ma.us (John R. Levine) writes:
> ... w.r.t. the IBM 360 architecture ...
>(Yes, it also had things like edit-and-mark which is a disaster in a paging
>system, they weren't totally prescient.)
>
EDMK was an implementation problem on early IBM 370s with virtual memory,
because the length of the area to be modified could only be determined by
trial execution, while address translation exceptions were required to nullify
all side-effects of the instruction. But this isn't a problem in modern
implementations (e.g. IBM 308x and 3090) which have general mechanisms for
rolling back the logical state of of a CPU, including recent storage
modifications.

Chris Thompson
JANET:    cet1@uk.ac.cam.phx
Internet: cet1%phx.cam.ac.uk@nsfnet-relay.ac.uk