Author: Bo Persson
Date: 04:24:02 07/03/03
Go up one level in this thread
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. When Motorola tried to do the same trick, and extend their 6800 to a 68000, they very soon found that it didn't work for them either. Unlike Intel, they went back to the drawing board and did a complete redesign with 32 bit registers. Very beautiful, but maybe it caused it to arrive too late... You can even see that Intel's 32 bit register names EAX, EBX, ECX are now twice extended from their 8 bit origin. Bo Persson bop2@telia.com
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.