Reproducing old machines with newer technology (Re: PDP-12 at the RICM)

ben bfranchuk at
Tue Jul 14 21:42:41 CDT 2015

On 7/14/2015 7:36 PM, Jon Elson wrote:
> On 07/14/2015 07:44 PM, William Donzelli wrote:
>>> IIRC, the KB11 processors used in the DEC 11/45 and 11/70 (and other
>>> related systems) used five "clocks delayed from each other" (more
>>> commonly known as clock phases).
>> IBM used this method as well on many of their machines.
> On the system 360 CPUs, they did not use flip-flops like we are used to,
> today.  They used latches, making it a requirement that there be at
> least two clock phases in most of the CPU, so that data into the ALU,
> for instance, remained stable when some register at the output was
> clocked.  Since these were discrete transistor implementations, a real
> flip-flop was too expensive, but a latch could be implemented in about 6
> transistors, I think.

I guessing ( no schematic handy) that they made the 360 register file
easy to decode and build with latches.

> The 11/45 used TTL ICs, so real FFs were available in that technology,
> although they may have used latches as well.

I have seen some 11/?? schematics on bitsavers that the alu uses AOI gates
and includes a latch term.

> Jon

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