Author: Tom Kerrigan
Date: 10:20:32 07/01/03
Go up one level in this thread
On July 01, 2003 at 11:57:58, Robert Hyatt wrote: >On June 30, 2003 at 21:03:30, Tom Kerrigan wrote: > >>On June 29, 2003 at 23:50:11, Robert Hyatt wrote: >> >>>On June 29, 2003 at 06:35:02, Tony Werten wrote: >>> >>>>On June 28, 2003 at 14:23:50, Robert Hyatt wrote: >>>> >>>>>On June 28, 2003 at 12:12:15, Jay Urbanski wrote: >>>>> >>>>>>On June 28, 2003 at 10:33:45, Robert Hyatt wrote: >>>>>> >>>>>>>Those are not true 64 bit processors. Supposedly 32 bit stuff runs just >>>>>>>fine on them, but they have 64 bit extensions. >>>>>> >>>>>>How is Opteron not a true 64-bit processor? >>>>> >>>>> >>>>>Because it executes 32 bit instructions _also_. >>>> >>>>P4 and AMD also execute 16-bit instructions, so they are 16 bit processors ? >>> >>>Not pure 16 bit no. Not pure 32 either. >>> >>>Check out "Cray" for a better example of a pure architecture. >>> >>>All math is 64 bits. All address arithmetic is 32 bits. Different >>>instructions, functional units, and registers for each. No kludges about >>>gating 32 bits with 32 high-end zeroes and that kind of stuff. >>> >>>But in the case of opteron, at least at first look, it appears to be a 32 >>>bit machine with 64 bit instructions layered on top. >> >>Are you kidding me? >> >>The "bitiness" is the width of a chip's datapath, right? > >Yes. But there is more. A chip made to do 64 bit operations as its _normal_ >mode of functioning is a 64 bit chip. A chip that does 32 bit operations >normally, with 64 bit add-ons, is not really a _full_ 64 bit chip. > >That was, and is, my point. How do you figure that the Opteron/PA-RISC/UltraSPARC/MIPS/POWER do not do 64-bit operations as their "normal" mode of functioning? They have 64 bit registers and the values in those registers are communicated over 64 bit busses to 64 bit buffers and 64 bit latches and 64 bit ALUs. How can you possibly get more 64 bit than that? Just because all of this hardware _can_ be utilized to also execute 32 bit instructions (the same way a chip does a "2 bit instruction" when you calculate the sum of 1 + 1) doesn't mean it's not a 64 bit chip. Conceptually, all of these ISAs can be viewed as "add-ons" or "extensions" if you're going to make a PowerPoint block diagram, but that has no bearing on the design of the processor. All of these chips can decode 32 or 64 bit instructions (with mostly the same logic, in fact) equally fast. Saying "add on" makes it sound like the 64 bit instructions must first be translated to 32 bit instructions or something. >>The Athlon and Pentium quite obviously have a 32 bit datapath so they are 32-bit >>chips. The Opteron has a 64 bit datapath so it's a 64-bit chip. >> >>I don't know what you mean by "64 bit instructions layered on top." >> >>-Tom > >It runs X86 natively. That is a 32 bit instruction set. So does IA64, although you apparently didn't realize this. -Tom
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