Author: Robert Hyatt
Date: 16:20:04 07/03/03
Go up one level in this thread
On July 03, 2003 at 15:59:25, Tom Kerrigan wrote: >On July 03, 2003 at 07:24:02, Bo Persson wrote: > >>On July 02, 2003 at 19:29:45, Tom Kerrigan wrote: >> >>>On July 02, 2003 at 14:24:28, Robert Hyatt wrote: >>> >>>>>What x86 problems? The x86 has variable length instructions anyway, so you can't >>>>>say that n-bit-long instructions limit it somehow. >>>> >>>>Sure I can. It first limits the number of registers to 3 bits. I'd bet >>>>that if Intel could "start over" the ISA would be greatly different with a >>>>target of 32 bits from the beginning. Intel grew up from 8 bits. Other >>>>vendors started at 32 and their instruction sets are _far_ better. Motorolla >>>>is an example with the 680x0. The sparc has a nice instruction set, it's just >>>>a dog for performance. >>> >>>I don't know what in the world you're talking about. Grew up from 8 bits? Target >>>32 bits? Started at 32 bits? Do you know what "variable length instructions" >>>means? x86/680x0 didn't start at, target, or grow up from ANY length. >>> >> >>You are losing your history Tom! >> >>The 8086 project started out with the *specific* goal of being able to machine >>translate assembly language programs from its 8080/8085 predecessors. Eventually >>the idea didn't work out, but still heavily influenced the design of the x86 >>assembly language and the register set of the processor. AX, BX, CX, etc are >>eXtended versions of the 8-bit A, B, and C registers from the 8080. > >Of course. But that doesn't change the fact that the _instruction width_ was not >a limiting factor in designing the ISA. > >For some reason it seems to be very difficult to keep instruction width and >datapath width straight in this conversation. > >-Tom The "instruction width" on the X86 is pretty much irrelevant. One byte up for instructions. I have no idea what the longest instruction is on the X86 as I don't count the bytes although I'm sure I could find out.
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