Bay Area nerd/computer person. Found at https://www.roguelazer.com/ and primarily on the Fediverse at @roguelazer@hachyderm.io.

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Cake day: February 15th, 2025

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  • To answer your specific question: no. There have been and continue to be lots of CPUs that have things that could plausibly be called a “bit size” that aren’t a power of 2. Note that the “bit size” can refer to a few things (the width of the bus between the CPU and memory, the native size of a pointer, and/or the native width of the arithmetic units). I’ll give examples of each.

    On essentially every “64-bit” computer, the bus to memory is not 64 bits wide. For example, the Apple M4 ARM CPUs are 64-bit but have a 128-bit memory bus over which they communicate something like 43-bit physical addresses. ARM has always been this way; the original 32-bit ARM1 had 26-bit physical addresses.

    As to pointer size, the best example is probably the currently-being-developed CHERI architecture which is 64-bit arithmetic but 129-bit pointers.

    For an arithmetic unit example, the floating-point unit on Intel CPUs was traditionally 80 bits wide. These days, it’s emulated on a 128-bit wide SSE unit but you still see 80 bits in code a bit.