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Posted by Jeff on 05/22/06 07:24
Voinin <vboing@boing.biz> wrote in
news:127004nidbjfle7@corp.supernews.com:
>Jeff wrote:
>--
>Space is big. You just won't believe how vastly, hugely, mind-
>bogglingly big it is. I mean, you may think it's a long way down the
>road to the chemist's, but that's just peanuts to space. - Douglas
>Adams, The Hitchhiker's Guide to the Galaxy
>> Voinin <vboing@boing.biz> wrote in
>> news:126usca1t048m9c@corp.supernews.com:
>>
>>> When I record a DVD I turn verification on. (I got into the habit
>>> when I used a tape backup drive back in the day.) When the disc is
>>> being burned it starts out at 8x and finishes at 8x. So it seems
>>> that during burning it's using CLV mode. However, when the
>>> verification process is running the speed varies from slow to about
>>> 8x at the end. So it's apparently using CAV mode. But when I rip a
>>> single-layer DVD the download speed approaches 16x towards the end
>>> of the read. This process, too, apparently uses CAV mode.
>>>
>>> My question: Why does the verification process take longer to read
>>> than it does when burning or when ripping a DVD?
>>>
>>> FWIW I'm using Nero 7, but this phenomenon happens with other
>>> software I have used to burn discs.
>>>
>>
>> Because when you are verifying you are not just reading the DVD, you
>> are also reading the same files from the hard drive and spending a
>> bit of time comparing the two to see if they match. Your computer is
>> apparently not fast enough to do this at the maximum DVD read speed.
>Somehow I don't see this, especially since the DVD and the hard drive
>are on different IDE busses. The system easily has the throughput to
>be able to perform both operations at the same time. Consider also
>that reads are much faster than writes and the verification process
>only involves reads from both media.
The verification process involves MORE than reads from both media.
1. Even if you are, as you assume, reading from both drives at once, the
reads are not going to be synchronous. The busses are not necessarily
working at the same speed and unless you just defragged the hard drive
the heads will have to move around to where the parts of the files are
stored while the DVD reads a more or less continuous track. You might
be accessing virtual memory which would add more reads and writes to
slow the hard drive.
2. You are reading parts of the files into memory and then the reading
STOPS briefly while the CPU processes the two sets of data in memory
before it reads some more.
3. Throughput is not just IDE channel speed. You have to consider the
whole system: RAM access, CPU speed, chipset, virtual memory access,
video. Somewhere along the line one of these could limit the speed of
your verifying.
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