Author: Tony Werten
Date: 07:54:07 07/03/03
Go up one level in this thread
On July 03, 2003 at 09:37:38, Robert Hyatt wrote: >On July 02, 2003 at 12:29:18, Vincent Diepeveen wrote: > >>On July 01, 2003 at 16:02:40, Robert Hyatt wrote: >> >>>On July 01, 2003 at 13:20:32, Tom Kerrigan wrote: >>> >>>>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. >>> >>>No, but it _very likely_ means that the design has some trade-offs to make the >>>32 bit stuff work. IE it is simply easier to do everything in 64 bit mode >>>rather than having to special-case some 32 bit stuff using the same registers, >>>as then there are all the normal sign-bit problems, to name just one issue. >>> >>>Note that I didn't say that the opteron was trash. Far from it. I simply said >>>that I doubt it is a pure 64-bit processor, since it was first designed to be >>>compatible with the X86 (poor) architecture, and then had 64 bit supported >>>added on top. >>> >>>The X86 architecture itself is bad enough. >>> >>> >>>> >>>>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. >>> >>>Not what I implied. Having to execute instructions designed for 32 bits >>>requires some concessions that a pure 64 bit machine doesn't have to deal >>>with. Again, the Cray is the perfect example, in that even though it does >>>both 32 and 64 bit stuff, 32 bit for addresses only, and 64 bits for math >>>only, everything is _clean_ and there are no worries about doing any 32 bit >>>stuff on the 64 bit functional units, etc. >>> >>> >>> >>> >>>> >>>>>>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. >>> >>>No I didn't, although I am not an IA64 person. However, how does a VLIW >>>architecture execute mov al,x type instructions? If the hardware can do >>>that it would be interesting. If software has to do some translation then >>>it would be a kludge like the alpha/vax solution. >>> >>>But if you can throw in X86 instructions into the mix of normal Itanium >>>instructions, that would suggest more than just a kludge. >>> >>>> >>>>-Tom >> >>It is incredible to see how so much nonsense can be written by you Bob, just >>because you are too stubborn to admit that the opteron is a 64 bits chip. It >>even has its own x86-64 bits instruction set for that. >> >>The sucking itanium-madison 1.3Ghz chips are also 64 bits depite that they are >>downwards compatible to execute IA-8 bits code. No one calls that a 8 bits chip! >> >>Though it is not worth more than 8 pennies. It cannot execute correctly >>scientific software at all. All the big benches run at it currently produce >>wrong results after long runs. Of course most benches like specint/specfpu do >>not verify that a result is obtained correctly. Yet it is not called a buggy cpu >>it is not called a 8 bits cpu it is not called a 32 bits cpu, but it is a 64 >>bits cpu. >> >>Perhaps let's try the approach most people use with childs: >> The opteron is a 64 bits chip. Period. > >It's a 64 bit chip with some kludges that allow it to execute X86 32 bit >stuff. > >That's what I said to start with after I clarified my comment. The documentation seem to indicate there is another possibility, but maybe I'm not getting it. From what they write I understood you can run legacy stuff (32 bit ) or full 64 bit (on a 64 bit os). In case 1 you do have 16 registers but they are 32 bit, in case 2 you have 16 64 bit registers. That would indicate that only on 32 bit you have the kludges, but on 64 bit it is "pure", ie the 32 bit is an "extension" of the 64 bit and not the different way around. Tony > > >> >>Best regards, >>Vincent
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