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From: hyc@math.lsa.umich.edu (Howard Chu)
Newsgroups: alt.folklore.computers
Subject: Re: non-volatile core memory
Message-ID: <10675@stag.math.lsa.umich.edu>
Date: 17 Jan 90 00:13:42 GMT
References: <10257@microsoft.UUCP>
Sender: news@math.lsa.umich.edu
Reply-To: hyc@math.lsa.umich.edu (Howard Chu)
Organization: University of Michigan Math Dept., Ann Arbor
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UUCP-Path: {mailrus,umix}!um-math!hyc

In article <10257@microsoft.UUCP> markro@microsoft.UUCP (Mark ROBERTS) writes:
>compiling and linking on the current system; loading the result into core;
>pulling out the memory board; walking accross the lab and inserting the
>board into the new machine; using the debugger jump to know address.
>
>Needless to say, got more testing done after they brought O/S up on new
>system.

Different scale, of course. HP calculators are all CMOS devices these
days, eh? The HP-41 was cute, 'cause you could take their little memory
modules out, swap them with someone else's calculator, and presto, instant
file/data transfers. Of course, with the original 41Cs, that was only
64 registers == 448 bytes per module, and when I started messing with 'em,
folks were using CVs, with the equivalent of all 4 modules already installed.
(*Only* 4 ports in back. I wish some well-known computer companies would
offer as much!!) But hey, then HP came out with Extended memory modules
for the 41, and the trick returned. Dunno why they called it X-memory,
it mapped in at the other end of the address space but you could still
use it directly. Execute code out of it, etc. (Using synthetics tricks,
that is. You had to alter the memory map, effectively turning the address
space upside down. If you weren't careful about it, the PACK routine that
packs unused memory would start at the top of RAM, wrap around thru zero,
and wham - all gone. The dreaded MEMORY LOST...)

But anyway, these modules were a lot more fun, holding, what, 2K each?
Cool stuff.

Wonder what kind of chips they used, always tossing in memory in
multiples of 448 bytes. This carried on thru the HP-10 series as
well (10, 11, 12, 15, 16, etc.)
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