
What Makes a PDP-11/35 Tick? - bcaa7f3a8bbc
https://loomcom.com/blog/0044_what_makes_a_pdp_11_35_tick.html
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tyingq
Somewhat related, here's a 6502 compatible CPU made from a bunch of ttl logic
chips: [https://c74project.com/](https://c74project.com/)

It even boots up in a VIC20, and can run at 20x the clock speed of the real
6502.

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amelius
Neat. Makes me wonder if in 25 years, hobbyists will build a 64 bit Intel x86
CPU entirely in ttl logic, at 20x the clock speed.

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greenyoda
A modern x86 CPU built out of TTL logic would be huge, slow and use lots of
power. Comparing number of transistors:

\- 6502: 3500 transistors[1]

\- Intel Core i3: 382 million transistors,[2] or roughly 191 million
transistors per core.

So a single core of a modern x86 processor built with TTL would have 55,000
times the number of chips of a TTL 6502. Most people wouldn't have the space,
power or cooling capacity to run that.

Also, it would be much slower than a single chip x86 CPU, since it takes time
for signals to travel between discrete chips, due to having to drive the
capacitative loads of the I/O pins (and traverse a much larger distance).
There's no way that TTL could run at gigahertz clock rates.

The only reason why a 6502 made of TTL can be faster than a real 6502 is that
the 6502 was a very slow processor. Its clock speed was only 1 - 3
megahertz.[1]

[1]
[https://en.wikipedia.org/wiki/MOS_Technology_6502](https://en.wikipedia.org/wiki/MOS_Technology_6502)

[2]
[https://en.wikipedia.org/wiki/List_of_Intel_Core_i3_micropro...](https://en.wikipedia.org/wiki/List_of_Intel_Core_i3_microprocessors)

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perl4ever
Aren't most of the transistors in a modern CPU used for cache, not to mention
additional processing units?

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greenyoda
I accounted for the additional processing units by dividing the number of
transistors by the number of processor cores on the i3 chip (there are two).

Since the question was asking about getting performance that's comparable to
the original processor, we'd need to keep the cache.

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davidgould
I don't think you need to keep all the cache.The cpu will be much slower due
to the slower chips and propagation delays so it will be much better matched
to memory speeds. Which would make cache misses much less important.

