Accuracy of IBM Instructional Logic Diagrams

[Jay Jaeger]

As part of my project to create a Field Programmable Gate Array
implementation (FPGA) of the IBM 1410 Data Processing System based on
Automated Logic Diagrams (ALDs), I decided to look at using the
Instructional Logic Diagrams (ILDs) to guide my testing, rather than
using the ALDs directly.

The ILDs are written completely in “positive logic”. Going in, I sort of
expected a pretty imperfect match – that the ILDs would not have all the
signals, and be somewhat superficial in their treatment of the logic.
For the IBM 1410, the circuits were:

	AND, OR, Inverter, Indicator (Lamp), Single Shot,
	Latch (Reset/Set), Trigger (Flip Flop)

To my surprise I found that the ILDs are *VERY* accurate, and a great
testing guide, providing a second view of the logic – a kind of
redundancy check against my entry of ALD data into my system. They are
good enough that they have given me considerable confidence that I can
use them to help “fill in the blanks” related to the handful of ALD
pages I am missing, and also for some of the IBM 1414 peripheral
controllers for which I do not have ALDs.

In 1962 IBM published an article in the IEEE Transactions “Information
Processing — from Engineering Drawing to Manufacture” by R. K. Grim that
describes how the data the ended up generated ALDs was entered and the
ALDs produced, but it does not mention where the ILDs come from. They
are definitely artwork – not machine generated per se. The article did
not address ILDs.

I have corresponded with IBM to see if they might have, in their
archives, the data from these 1960s era engineering systems, but it
seems that they do not (or have lost the pointers to them.)

It seems that the SMS automation was first done using an IBM 709, then
they later added IBM 7090 and IBM 1401 systems (which of course could
not have been there for the original design of the IBM 7090 and 1401,
which used the SMS system), using tape files. The article also describes
future plans to use a 1301 disk drive attached to an IBM 1410 for remote
(tele-processing) access (which was supported by the IBM 1410-PR155
operating system.

The accuracy of the ILDs is such that I expect that they evolved along
with the design of the machine and entry of the data used for the ALDs.
I’d expect that doing it after the fact, from the ALDs, would be quite
error prone — besides the one difference I have found is in the signal
names, which do not always exactly match those used in the ALDs, but are
close enough that the intent is obvious. But I don’t know the timing:
which came first — the ILDs or the ALDs, or did they perhaps begin
together in some form and co-evolve?

In summary, it seems to me that one could do a pretty decent positive
logic implementation of IBM machines of that era using these ILDs. This
was a real eye-opener.

If there are any old-time IBMers that read this, I'd love to hear any
enlightening information or stories about this process.

JRJ