Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!usc!apple!amdcad!weitek!weaver From: weaver Newsgroups: comp.arch Subject: Re: why is 33 MHz a popular number? Message-ID: <1990Nov28.021703.28668@weitek.COM> Date: 28 Nov 90 02:17:03 GMT References: Sender: weaver@weitek.COM (mike weaver) Reply-To: weaver@weitek.UUCP (Michael Weaver) Organization: WEITEK Corp. Sunnyvale Ca. Lines: 22 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 There is no hardware magic about 33 vs 32, and so forth. This is competitive marketing. When you manufacture chips, the max speed for the individual chips makes a bell curve, with small numbers of very slow and very fast chips, and most in the middle. If the middle of the curve is (say) 30 Mhz, you make your chip 33 Mhz by testing for speed and throwing out any that are slower than 33 (or more likely retesting them for 25 Mhz). Of course if the middle of the curve is too low, you won't get any at the desired speed. The magic number is actually the approximate 20% improvement in speed, which probably has to do with how much speed improvement is necessary to make a difference to buyers of the chip.