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Board from 60's early military computer: UNIVAC CP-901

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radiogeek381:
The choice of DTL in the late '60s (if it was produced mid-70 then the design likely was "in the box" by 1969 - perhaps much much earlier) could have been influenced by the availability or qualification of mil-spec qualified parts in the 5400 series (TTL) or COS/MOS. Often a system manufacturer would have a "qualified parts list" that meant they had incoming test systems in place, the chip supplier had their own tests, the parts had been characterized across voltage and temperature, the datasheets were "accurate," there had been lifetime tests, and the supplier could commit to timely delivery of parts in production quantities as long as the computer was in the catalog. 

All that takes time.  So a technology that showed up in 1969 from a chip vendor would not likely have been qualified before '70 or even later. (Perhaps there are counter-examples? Those would be interesting.)

I'm noting the Fairchild 900 series was nominally 5V and unipolar. (No negative supply.). The open collector outputs would likely have been compatible with early TTL, and maybe even older RTL and diode logic modules. 

As crude as these devices seem, they may have been faster than early-70s CMOS.  A 2 input CMOS NAND in '75 had a max prop delay of 100 ns (better than I remembered) with a very limited fan-out. The input loading of a CMOS gate was about 2x the comparable DTL 2 input NAND. And the advantage for DTL was about 2x per pF of load.

There were likely a lot of reasons to choose DTL at the time, other than inertia. But inertia probably played a part.

Alex Eisenhut:

--- Quote from: SeanB on August 25, 2023, 05:28:23 pm ---International to me, though it is expensive.....

--- End quote ---

I mean what I see in the item description once you scroll down. Still no reply from the seller.

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