Calculating Pi Digits on First Intel Microprocessor (Intel 4004)
owl writes:
https://mark.engineer/2022/04/calculating-pi-digits-on-first-intel-microprocessor-intel-4004/
One day I thought about the performance gap between the first Intel processor and modern machines. Of course, we can try to do some estimations empirically - we know clock rate and how the pipeline is organized and what features intel 4004 CPU has (but it would not be standard FLOPS, because there was no embedded support for float numbers yet). But there are few details: architecture bit width (only 4 bits in comparison with modern 64 bits!), very limited instruction set (it's missing even basic logical operators like AND or XOR) and peripheral limitations (ROM/RAM accesses).
So I decided to research the subject in practice. After some thinking, I chose number calculation as a benchmark. After all, even ENIAC did that (in 1949) and achieved a new record for the amount of calculated digits.
Usually, we chose hardware, based on our goals. But in that case, we need to choose an algorithm, based on restrictions that come with intel 4004. So what do we have?
CPU is very basic and its instruction set has very few ALU operations - addition/subtraction of 4-bit operands, inversion (NOT operator), rotation left/right. And ... that's all, folks. No multiplications, division or any other logical operators.
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