Author: Robert Hyatt
Date: 16:18:36 07/03/03
Go up one level in this thread
On July 03, 2003 at 15:54:34, Tom Kerrigan wrote: >On July 03, 2003 at 09:35:41, 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. >> >>Sorry, but the X86 _started_ as an 8-bit cpu capable of doing 16 bit math. >>It grew to 16 bits in the 80286 and 32 bits in the 80386. But it was >>originally an 8 bit ISA. > >Wrong, the 8086 (the first x86) is a 16-bit processor. The 8088 used in the >original PC was a variant of the 8086 with an 8-bit data bus, maybe that's why >you're confused. The _first_ was the 8080 and it was _not_ a 16 bit cpu. The 8086 was the second processor and it was compatible with the 8080. Each 80X86 processor ever since has maintained that compatibility. But it _started_ at 8 bits. The 8088 was a kludge, but it wasn't where I was talking about either. I was talking about the _beginning_ of the product line which went back to the original 8080 which the current processors will still execute assembly code from. > >But now you're confusing instruction length with datapath width. Check the top >of this post. We were talking about instruction width. Somehow you changed it to >datapath width. Nope. 8080 was 8 bit everything, but with 16 bit registers. 8086 was 16 bits. 80186/286 were better. etc... but all are backwardly compatible in terms of ISA. > >-Tom
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