Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!usc!apple!amdcad!mozart.amd.com!proton!tim From: tim@proton.amd.com (Tim Olson) Newsgroups: comp.arch Subject: Re: why is 33 MHz a popular number? Message-ID: <1990Nov27.230643.11637@mozart.amd.com> Date: 27 Nov 90 23:06:43 GMT References: Sender: usenet@mozart.amd.com (Usenet News) Reply-To: tim@amd.com (Tim Olson) Organization: Advanced Micro Devices, Austin, TX Lines: 20 In article tom@ssd.csd.harris.com (Tom Horsley) writes: | I see a lot of the current and near current top of the line RISC chips and | other microprocessors coming out with a 33MHz clock rate. In a similar way | the previously most popular number seemed to be 25MHz. | | Is there some hardware related magic about certain clock rates that makes it | likely for totally different manufacturers of totally different chips to | come out with chips with the same clock rates in similar time frames? | Obviously they all need to stay competitive, but why do they lots of them | wind up at exactly 33? Why not 30 or 35? It's mainly that designers think in terms of clock period (ns) rather than frequency in MHz, and 33MHz (really 33.3333...) is a 30ns cycle, just as 25MHz was a 40ns cycle. 40ns -> 30ns is a 25% reduction in cycle time. -- -- Tim Olson Advanced Micro Devices (tim@amd.com)