Re: ancient OS history, ARM is sort of channeling the IBM 360

John Dallman wrote:
>

In article <v5rcui$fqgj$1@dont-email.me>, tkoenig@netcologne.de
(Thomas Koenig) wrote:
>

Imagine a process which resides at a certain address.  It contains
code, data, and pointers to data.  Now you swap it out and want
to reload it.  You can use the same base address, then everything
is fine.  Or you can use a different one, where do the pointers
point, especially registers which contain addresses?
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The /360 tried to solve this via base pointers, which all addresses
were supposed calculated relative to to.  Hence the RX and RS
instraction all had a base register + 12 bit offset for their
addressing modes - swapping out the base registers (if you knew
which ones they were, was this info in the executable?)  should have
worked.  But the SS instructions for decimal arithmetic did not have
base pointers, so that solution did not work in the general casse.

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And only a 12-bit offset, to boot. I've read of systems with base and
limit registers, where all accesses were offsets from the base (or
separate base registers for code and data).

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Yes, e.g. Univac 1108.