Date: Sun, 11 Oct 1998 13:50:24 +0200 (CEST) From: torstenb@vmunix.org (Torsten Blum) To: garbanzo@hooked.net Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: how fast are "fast" CDROM drives ? Message-ID: <m0zSK12-0006AJC@onizuka.vmunix.org> References: <199810101313.OAA16631@labinfo.iet.unipi.it> <Pine.BSF.4.00.9810101445130.13820-100000@zippy.dyn.ml.org>
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In freebsd-hackers you write: >Well, some of the earlier high speed CDs 12x+ cheat a bit by rotating the >disk faster only for certian parts of the disc (the outter edges IIRC). That's wrong, sorry. Drives between 1x and 8x work in CLV mode (Constant Linear Velocity). They always read the sector as the same speed. On the outer edges the disc spins slower to get the same datarate it gets on the inner edges. Faster drives (12x and above) work in CAV mode (Constant Angular Velocity), which means that the disc always spins at the same speed. If you read sectors from the outer edges of a cd it's faster than on the inner edges. On a CD, the sectors start on the inner egdes, so you only get 32x on a full CD. I wouldnt call CAV "cheating". The problem are hardware vendors who want to sell the "fastest" drives, so they use the highest speed the drive supports, and that's 32x. -tb To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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