Author: Tom Kerrigan
Date: 12:59:25 07/03/03
Go up one level in this thread
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
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