RISC Vs. CISC Is the Wrong Lens For Comparing Modern x86, ARM CPUs

Long-time Slashdot reader Dputiger writes: Go looking for the difference between x86 and ARM CPUs, and you'll run into the idea of CISC versus RISC immediately. But 40 years after the publication of David Patterson and David Ditzel's 1981 paper, 'The Case for a Reduced Instruction Set Computer,' CISC and RISC are poor top-level categories for comparing these two CPU families.

ExtremeTech writes:

The problem with using RISC versus CISC as a lens for comparing modern x86 versus ARM CPUs is that it takes three specific attributes that matter to the x86 versus ARM comparison — process node, microarchitecture, and ISA — crushes them down to one, and then declares ARM superior on the basis of ISA alone. The ISA-centric argument acknowledges that manufacturing geometry and microarchitecture are important and were historically responsible for x86's dominance of the PC, server, and HPC market. This view holds that when the advantages of manufacturing prowess and install base are controlled for or nullified, RISC — and by extension, ARM CPUs — will typically prove superior to x86 CPUs.

The implementation-centric argument acknowledges that ISA can and does matter, but that historically, microarchitecture and process geometry have mattered more. Intel is still recovering from some of the worst delays in the company's history. AMD is still working to improve Ryzen, especially in mobile. Historically, both x86 manufacturers have demonstrated an ability to compete effectively against RISC CPU manufacturers.

Given the reality of CPU design cycles, it's going to be a few years before we really have an answer as to which argument is superior. One difference between the semiconductor market of today and the market of 20 years ago is that TSMC is a much stronger foundry competitor than most of the RISC manufacturers Intel faced in the late 1990s and early 2000s. Intel's 7nm team has got to be under tremendous pressure to deliver on that node.

Nothing in this story should be read to imply that an ARM CPU can't be faster and more efficient than an x86 CPU.

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