Re: architecture, The Design of Design

John Levine <johnl@taugh.com> schrieb:

I wonder if that was the way that the 704 OR'ed the index registers.
There were three of them, numbered 1, 2, and 4, so if your index field
was 5, it OR'ed registers 1 and 4. It subtracted the index (or the
OR'ed combination of indexes) from the base address, so it would have
taken some really tricky programming to make use of that. But someone
must have since they documented it and it continued to work on the
709, 7090, and 7094 until they provided 7 index registers and a mode
bit to switch between the old OR and the new 7 registers.
>
I have never found anything that says whether it was deliberate or an
accident of the 704's implementation, and I have looked pretty hard.

We've had that discussion before :-)

Looking at the "manual of operation" from 1955, the ORing is shown,
and it is not listed in the changes from the 1954 version

So, documented from the release, at least.

The (incomplete) schematics at Bitsavers will probably show the
ORs, if anybody can dig through them and the relevant drawings
are not in the missing parts. I can read "AND" and "OR", but I have
no idea what "CF", "T" or "2PCF" stand for.