[TUHS] SPARC is CRAPS spelled backwards.

Peter Jeremy peter at rulingia.com
Tue Sep 25 05:46:47 AEST 2018

On 2018-Sep-23 17:17:35 -0400, Paul Winalski <paul.winalski at gmail.com> wrote:
>In general, a CISC instruction set encoding can express the same
>algorithm more compactly than a RISC instruction set.  Once CISC
>technology solved the instruction pipelining and decoding problem, it
>gained an advantage over RISC architectures such as Alpha because the
>instruction set stream was less verbose.

RISC architectures have another advantage that instructions are always
aligned on known boundaries (typically 2 or 4 bytes).  This simplifies
the logic around (pre-)fetching instructions.

>Modern x86 designs have a
>bit of logic stuck in one corner that translates the x86 instruction
>stream into a string of RISC-style micro-operations.

Where "modern" is "this century".

>the best of both worlds--the compactness of a CISC instruction stream
>and the simpler and faster circuitry of RISC.

In the specific case of x86, I would dispute that.  The various warts in the
x86 instruction set and "architecture" mean that x86 code density is
relatively low and on a par with SPARC code.  I agree that the overall
performance is impressive but that is more a measure of the abilities of
Intel's engineers than the overall approach.

Peter Jeremy
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 963 bytes
Desc: not available
URL: <http://minnie.tuhs.org/pipermail/tuhs/attachments/20180925/d8225df5/attachment.sig>

More information about the TUHS mailing list