top left Image    Area, where does it go ?

Something I find quite interesting is how the transistors (and area) of the Megaprocessor splits among the different kind of activity. In particular we think of processors as being all about doing calculations but the ALU forms only a small part of this processor.
Looking at the transistors for the processor (leaving out the RAM) the counts are:

Transistor Count
Proportion (%)
Multiplexing 5174 34
Control Logic 4031 27
Adders, Logic, Shifters 2280 15
Cosmetic (module bus input display) 1904 13
Registers 1808 12

The biggest proportion of transistor usage, a third, is steering the data around . We have also about a third of the transistors dedicated to working out what we're supposed to be doing. Only about a sixth of the processor is actually doing productive work.

I don't quite know where to go with the observation, but I find it interesting....

One thing I certainly should have done (hindsight is great) is given the PC its own dedicated adder. It did have early on but the adder migrated into the ALU (it became ADDER2) so I could share it with other operations. This was a mistake. Adders are big, but so are the multiplexors. And there's also the yards and yards of ribbon cables I needed to move data from the PC to the ALU and then bring the answer back.

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© 2014-2016 James Newman.