rmwd wrote
Are modern CPUs built using these low level logic gates? ... its hard to imagine engineers at Intel for example making i5's using NAND gates?
They do use a lot of Nand gates, but there are other circuits available that are often more efficient than Nands.
Nor gates can both be created, but physics favors Nand gates because their transistors are smaller. In some circumstances Nor gates may be preferable. N-input Nand/Nor gates require 2N transistors, Not is just a 1-input Nand. However, that pesky physics requires transistor size increases as N increases. This means the gates grow in size by O(N^2) so there's a practical limit how large N can be.
Besides Nand and Nor, it is possible to make more complex gates with approximately the same speed as a Nand or Nor. An example is an And-Or-Invert gate which computes !(a b + c d). The Nand only implementation requires 3 Nands and a Not (14 trans.) with 3 gate delays. An optimized And-Or-Invert requires only 8 transistors and 1 gate delay, and is about the size of three 2-input Nand gates.
Another gate that CMOS can make with 2 transistors is a "transmission gate" which is like a logic controlled switch. They are very handy for multiplexors. A 2-input mux can be made with 2 TG and 1 Not: 6 transistors and slightly more than 1 gate delay. The equivalent Nand implementation would require 14 transistors with 3 gate delays.
The other thing that makes IC engineers jobs possible is Synthesis tools (Hardware compilers) that like Software compilers know the rules for the target IC technology and are very good at optimizing.
I just googled this: a 15-Core Intel Xeon Ivy Bridge-EX has 4.3
Billion transistors! That's a bit mind-blowing.
--Mark
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