Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!ukma!nrl-cmf!cmcl2!brl-adm!umd5!mimsy!oddjob!gargoyle!ihnp4!alberta!auvax!rwa From: rwa@auvax.UUCP (Ross Alexander) Newsgroups: comp.sys.atari.st Subject: Re: Floppy drive speed Message-ID: <417@auvax.UUCP> Date: Tue, 24-Nov-87 10:43:23 EST Article-I.D.: auvax.417 Posted: Tue Nov 24 10:43:23 1987 Date-Received: Sat, 28-Nov-87 10:47:39 EST References: <797@ssc.UUCP> <2053@dasys1.UUCP> Organization: Athabasca U., Alberta, Canada Lines: 30 Keywords: disk speed strobe tester caution Summary: a kluge or twain re drive speeds Muke Schuster and others have written about setting drive speeds, et c., and the fact that strobe wheels are a a good deal more accurate than DSPEED.TOS or whatever. Fine. But there has been an unspoken assumption all along, and that is: You want your drive to be going _exactly_ 300 RPM. I question this. Yes, that's the specification alright, but there is a good reason to run your drives a little bit SLOWER (say, 297 RPM or so). The reason is thusly: if you are using one of those clever formatters, such as DCFORMAT or any of its ilk, that can put 10 sectors on a track, the last gap (Gap #4, made out of 0x4e's) gets a little bit shorter than normal, which is 1401 bytes; it gets trimmed down to 780-odd bytes. It's not a bad idea, however, to run slightly larger than normal Gap 3's (normally 40 bytes, I like to double this), and then Gap 4 really gets crowded. But if you run the drive a little slow, the effect is that to the 1770, all the tracks look a little longer than normal, and you get your Gap 4 size back to something reasonable. You can check this by looking at the data coming off the read line with an oscilliscope (take the scope sync input from the index pulse line) and noting how close the end of the last sector comes to the end of the track. I have done this routinely for years and find it doesn't generate any trouble if you are only 1 or 2% slow; the PLL in the data separator can handle this kind of an error with it's eyes closed, and the added security of the longer gaps helps to overcome all kinds of write-skew and drive wow-and-flutter problems. Ross Alexander @ Athabasca University, alberta!auvax!rwa