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Date:      Sat, 10 Oct 1998 16:29:13 -0700
From:      Haze <dionn@spiritone.com>
To:        Alex <garbanzo@hooked.net>
Cc:        Luigi Rizzo <luigi@labinfo.iet.unipi.it>, hackers@FreeBSD.ORG
Subject:   Re: how fast are "fast" CDROM drives ?
Message-ID:  <361FEDC9.613F95FC@spiritone.com>
References:  <Pine.BSF.4.00.9810101445130.13820-100000@zippy.dyn.ml.org>

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On 10-Oct-98 @ 21:46:29, Alex <garbanzo@hooked.net> wrote:
> 
> On Sat, 10 Oct 1998, Luigi Rizzo wrote:
> [...]
> > I got a 32x ATAPI unit one month ago and there is no way (under
> > -stable) i can get more than 2.2MB/s by dd'ing from the disk.
> > Considering i get 5-6MB/s from a raw IDE disk (and from iozone with
> > large files) on the same machine, i don't think the limiting factor is
> > CPU or the OS.
> >
> > I wonder if anybody is able to exploit the speed of their 24/32/40x
> > IDE or SCSI drives
> 
> 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).
> The most inner part of the disc would then be read at somewhere around 6x.

Drives over 16x are CAV (most are anyway).  This means that the listed
speed of 32x can only be achieved at the outermost tracks.  If you filled
a CD completely, then read from the very last files you would get 32x
throughput.  Consequently, you almost never see it IRW situations.

CAV drives will xfer the outermost tracks at about 2.2x the rate of the
innermost tracks.  So your 32x will get about 14x on the inside tracks.
A throughput of 2.2MB/s (~15x) is quite typical.  The best I've ever
seen on my 32x drives is ~3.7MB/s.

-- 
Knowledge is the perception of truth distorted by reality

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