Re: architecture, The Design of Design

Thomas Koenig wrote:

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.

I found a 704 glossary that defines:

CF  = Cathode Follower
PCF = Power Cathode Follower
THY = Thyratron

A quicky search finds cathode follower is a signal regenerator buffer
tube circuit for driving high fan-out loads.

Unfortunately I couldn't find any 704 documents which detail
its tube logic circuit designs.

BUT... in searching for "IBM 704 tube" I cames across this which
show a picture of a 704 logic circuit

https://computermuseum.uwaterloo.ca/index.php/Detail/objects/13

and says the 704 tube logic circuits were designed by someone named
A. Halsey Dickinson, AND it seems he also designed the 604 tube

which were circa 1948, and those are documented.
This document is dated 1958 so contemporaneous with the 704
and details the 604 tube logic circuits:

http://www.bitsavers.org/pdf/ibm/604/227-7609-0_604_CE_man_1958.pdf

It is possible the 704's "T" gate stands for what 604 called TR or
Trigger units, which appears to be what we today call an SR Latch.