On May 25, 2005, at 5:53 PM, Carl Lowenstein wrote:
I thought the "R" in ARM stood for RISC. But maybe that is only history.
It does, but take a look at the instruction set. The hallmark of "RISC" is single purpose instructions which tend to be easily decodeable by hardware. The hallmark of "CISC" is complex instructions which tend to require internal or operating system microprogramming. With RISC, for example, load from memory address in register was a single instruction. With CISC, a load from memory often had multiple address modes, computations of an index address, etc.
The classic example of a CISC instruction was the VAX "evaluate polynomial". Talk about a heavyweight instruction.
ARM hardware has specialized instructions like simultaneous add/ rotates, bit decoding, etc. Also very CISCy.
x86 kind of straddles the boundary. While the complex instructions and modes tend to still be there, they are now sufficiently slow that compilers avoid using them and generally confine themselves to the core RISC-like instructions.
-a -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
