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

Jon Elson elson at
Tue Jul 14 20:36:52 CDT 2015

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.

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


More information about the cctalk mailing list