Interesting article in Spectrum about IBM's System/360

Jay Jaeger cube1 at
Sat Apr 13 09:11:56 CDT 2019

On 4/12/2019 1:15 PM, Eric Smith via cctalk wrote:
> The article says:
> Poughkeepsie’s engineers were close to completing work on a set of four
>> computers known as the 8000s that were compatible with the 7000s.
> AFAICT, that is totally wrong. The 8000 series was completely INCOMPATIBLE
> with any of the 7000 series machines. In fact, most of the 7000 series
> machines weren't even compatible with each other, though the 7040 and 7044
> had partial compatibility with the 7090 and 7094.
> There are some 8000 documents on Bitsavers so you can see for yourself.

Furthermore, like the 8000 series would have been, the 7000 series (and
the 700 series, and the 1400 series, for that matter) was more of a
series of *technology* rather than a series of compatible computers.

The 7000 series used SMS ECL (current mode), at least in a lot of
places, whereas the 1400 series were essentially RTL with some DTL
sprinkled in on the 1410.

For example, the IBM 7010 was an IBM 1410 done up in 7000 series
technology (and was a compatible super-set of the 1410 and, via  a
toggle switch, the 1401).  It had no architectural relationship with the
7090/7094, nor did the 7070 or 7080, near as I can tell.

>From "The Genesis of the Mainframe" by Bob O. Evans (an extract from a
longer memoirs document, which was not itself published, to my knowledge)

"Flush with the success of the 1401 and the 1410 in process — I was not
willing to abandon those winners to join the 8000 series plan, which did
not sit right with me in the first place because the 8103, 8104, 8108
and the 8112 were architecturally incompatible and I was certain
compatibility was fundamentally important."

"By May 1961 I concluded the 8000 series would be a serious blunder, in
part because of the lack of compatibility within the systems family. I
did not buy Dr. Brooks’ arguments that recompilation would be acceptable
to make it possible for the programming from all the dissimilar
architectures of existing products to work effectively on the dissimilar
architectures of the 8000 series. There were other important reasons to
scrap the 8000 series plan including technology choice. Jerrier Haddad
backed my decision; the 8000 Series plan was killed."

My experience with a couple of magazine authors during my career tells
me that many of them do not understand much of what they are writing,
and errors like this 7000/8000 thing are common.

Another half truth in the article reads:  "The power of compatibility
was demonstrated in the fall of 1960, when IBM introduced the more
powerful 1410 to replace the 1401. Software and peripheral equipment for
the 1401 worked with the newer machine. "

That was only true to the extent that the 1410 included a 1401
compatibility mode switch, which literally changed the logic so that it
became a (somewhat faster) 1401.  In its normal 1410 position, it could
not run 1401 programs, and vice/versa.


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