Message-ID: <44039CEF.3060508@vilain.net>
Date: Tue, 28 Feb 2006 13:44:31 +1300
From: Sam Vilain <sam@vilain.net>
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To: "D. Hazelton" <dhazelton@enter.net>
Cc: Peter Gordon <codergeek42@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: CD writing in future Linux (stirring up a hornets' nest)
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D. Hazelton wrote:
>>>This value is also reported by the drive. I don't know about DVD drives,
>>>but for CD drives it is a multiplier. 1x == 256K/sec transfer off the
>>>disc [...]
>>For CDs, 1x is actually 150 KByte/sec.
> Well, I've been known to be wrong before, and this number was more based on 
> the fact that I once measured a sustained transfer rate of 1M/sec on a 4x 
> CDROM

Think about audio.  Single speed = 75 frames of 2352 bytes per second, 
or 176kB/s.  However with data tracks you only get 2k per frame/sector, 
so that works out to be 153kB/s.

Due to the CLV nature of CD-ROMs you may find the drive is faster 
reading some parts of the disc than others.

>>According to WikiPedia, the DVD speed rating is almost 9 times that of
>>CD speeds. I.e., 1x DVD is about 1.32 MByte/sec.
> This was based on DVDx16 == CDx48 - I'm guessing someone is doing some monkey 
> work if a DVD is 9x a CD and a 16x DVD can't hit that mystical 52x of my 
> favorite CDRW drive in pure CD read mode.

You can do a similar calculation with DVDs.  While I can't find a 
reference for the maximum DVD total bitrate of ~10Mbit/s, this at 1.25 
MByte/s this roughly agrees with the 1.32 quoted.

Sam.
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