From: jpero(a)sympatico.ca <jpero(a)sympatico.ca> It would eat power but it would not be that slow. The mos logic of the time was quite slow compared to the ttl of the time. I did do a 2901C version of z80 and it was much faster than the MOS version, not due to the 2901s as they were logic savers but the acutal speed bottleneck as well. I have seen photos of apple IIe prototype laid out on early pre-production logic board, one of that 40 pin chipset socket is hooked to a equally same size board filled to the 4 edges with tightly packed TTLs and few large ICs, I think it was shown in Byte as well as few other publicatons. Large board full of chips vs. 40 pin IC, same thing...Amazing! That was replaced by a 2000 or so gate array so thats were it all went. Also the proto was built of all SSI TTL making it less dense. I did some work like that in the early 80s. Logic was faster than you think. It's true to get to the sub 100ns range for serious cpus you have to get the interconnect problem out of the way. However for a fairly fast machine (4-10mhz clocks) there are many examples that are mostly ttl. For starters the PDP-8E ca. 1971ish executes instructions in 1.4uS for the base modes and that was SSI ttl on low density boards. FYI it was limited by the core cycle time not the TTL, I ran one at nearly twice speed easily with semicon memory. Allison