Author: Tom Kerrigan
Date: 17:27:41 07/03/03
Go up one level in this thread
On July 03, 2003 at 19:20:04, Robert Hyatt wrote: >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. Right, it's irrelevant except that's what we've been talking about. ">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." -Tom
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