Re: Identifying CPU and current OS
On Tue, Sep 30, 2025 at 12:41 PM Michael Stone <mstone@debian.org> wrote:
>
> On Tue, Sep 30, 2025 at 04:08:56PM -0000, Greg wrote:
> > In computing, a word is any processor design's natural unit of data. A word is
> > a fixed-sized datum handled as a unit by the instruction set or the hardware of
> > the processor.
>
> It has that definition (among others), one which mapped cleanly to
> historic processors, but which is much messier when dealing with modern
> CPUs. E.g., amd64 mostly has 64bit instruction operands and types, but
> there's also an 80 bit floating point type and with AVX-512 extensions
> has 512 bit registers and can transfer data to/from memory 512 bits at a
> time in a single instruction. So is the word size 512? 80? 64?
Maybe a small nit: when someone says a 32-bit or 64-bit machine, they
are usually talking about the size of a register in the register file
for the main CPU.
The 80-bit, 128-bit, 256-bit, 512-bit and friends are the size of
registers in coprocessors, like the x87 math coprocessor, the SSE
coprocessor, the AVX coprocessor, etc.
There is also a CHERI architecture
(https://www.cl.cam.ac.uk/research/security/ctsrd/cheri/cheri-morello.html).
They have 64-bit registers, 20 bits of bounds, 16 bits of object type,
and 18 bits of permissions. Effectively, pointers are 128-bit (64-bit
pointer, and 64-bits of capability describing the pointer). The GCC
Compile Farm offers a CHERI machine at cfarm240
(https://portal.cfarm.net/machines/list/).
There's also a memory word size on occasion. For example, Crays are
64-bit, but have 72-bit memory word size for error correction.
And based on OP's original question of "How do I discover the CPU's
bus width?", he probably should have asked how to determine the
register size of the CPU. I think that was closer to what he wanted
to know.
Jeff
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