Author: Gregor Overney
Date: 16:27:49 01/22/01
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.......... >>>why would you conclude that more instructions per cycle slows the cycle >>>down? Because the Intel does it? Different animals. Pentium = 64 bit >>>bus. Alpha=256. With much higher memory bandwidth to boot.. > >Exactly, the Alpha instruction set was also designed for this. .......... Why should the bandwith matter? It does not help you to cool your chip. BTW, I thought the PIV is using more than 64bit for the internal bus, but I might be wrong. Why I think there is a link between how many instructions a CPU can handle per clock cycle and its clock rate using a given process? More instructions per cycle -> bigger branch mis-prediction penalty, unless you improve dramatically the chip design. But the new chip-design that avoids mis-prediction's more effectively requires more transistors per surface area (it is a more complex design (or your chip size will increase -> needs more power to run it)) -> produces a greater challenge to cool your chip (proportional to number of transistors per surface area) -> forces you to switch manufacturing process or lower CPU cycle time (clock rate). Here, I make the assumption that they are using a standard process and do not switch to a new, untested process. I also assume that Compaq wants to ship this thing before 2010. ....Of course, Compaq coud attempt to make copper/gallium arsenide chips :-) I am not debating that in the future someone will actually run 8 instructions on a CPU running at 3GHz _and_ significantly improve performance. I just do not believe that it can be done today. The 21464 is a marketing hype. I first want to get my hands on a 21364, but the "best" workstation from Compaq runs only with a 21264. Why? I could also buy the PIII before the PIV was on the market. Or, an other example, I could also buy the USPARC II before USPARC III was available. - The 21464 is a white paper. I am sure that Intel, IBM, Motorola, TI, SUN, and others have similiar white papers to impress the community. The 21164 was a good chip. The 21264 is a great step forward. We will see if Compaq is able to continue what DEC was able to do. The 21364 sounds promising and seems to be available to selected customers. http://www5.compaq.com/alphaserver/workstations/xp1000/index.html Gregor
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