RISC versus CISC chip design

This is good example of the value of not letting edge cases cause a design to be over complicated - or the 80-20 rule.

The ARM processor architecture that dominates the mobile phone market now, and that Apple has now finally switched over to always had a superior design to the Intel chips it is replacing. It took 30 years but it’s finally happening.

The ARM chip was invented by British company called Acorn Computers (I have fond memories - my first computer was a BBC Micro produced by this company and I worked at McDonalds as a teenager to buy the Archimedes computer which was the world’s first ARM based computer).

What the designers at Acorn did is that they observed 80% of machine code only used 20% of the CPU instructions. The remaining 20% of the instructions could be implemented by using a few of the more common simpler instructions. By eliminating all the instructions that were not frequently used they were able to greatly simplify the chip design and make the ARM processor much less expensive, faster and consume less energy. They called this RISC - reduced instruction set computer versus CISC - Complex Instruction Set Computer.

It has taken a while to over come the legacy hold of CISC and Intels commercial dominance but ultimately RISC architectures are proving to be dominant in long term.