speed

[Dipl]

How fast dus a CD-rom turn ?

And suppose that a 1 speed CD-player turns (just as example) 100 rounds a
minute.
Is a doubles speed player then turns 200 rounds
and a 48 speed 4800 rounds a minute ?

 

[MCheu]

How fast dus a CD-rom turn ?

And suppose that a 1 speed CD-player turns (just as example) 100 rounds a
minute.
Is a doubles speed player then turns 200 rounds
and a 48 speed 4800 rounds a minute ?

Technically, the 1x speed rating for a CD-ROM is defined as a transfer
rate of 150kB/s. The X speed rating is a multiple of that, so 2x
300kB/s, 3x is 450kB/s, etc. How the manufacturer chooses to reach
the rated transfer rate is irrelevant, so the X speed rating doesn't
necessarily translate to how fast the disc is actually spinning. That
said, here's what the faq for CDSPEED2000 says about the rotational
speeds of modern drives:

http://www.cdspeed2000.com/go.php3?link=faq_general.html#q5

 

[Mike Walsh]

A 1x drive turns at 500 RPM at the inner edge of the disk and 200 RPM at the outer edge. A 48x drive turns at a constant 9,600 RPM. It operates at 48x only at the outer edge of the disk.

How fast dus a CD-rom turn ?

And suppose that a 1 speed CD-player turns (just as example) 100 rounds a
minute.
Is a doubles speed player then turns 200 rounds
and a 48 speed 4800 rounds a minute ?

--

When replying by Email include NewSGrouP (case sensitive) in Subject

Mike Walsh
West Palm Beach, Florida, U.S.A.

 

[Chris]

A 1x drive turns at 500 RPM at the inner edge of the disk and 200 RPM at
the outer edge.

How can the inner edge of a disk be doing more revolutions per minute than
the outside of the disk? or is it that the speed varies as it reads
different parts of the disk?

Chris D

 

[kony]

How can the inner edge of a disk be doing more revolutions per minute than
the outside of the disk? or is it that the speed varies as it reads
different parts of the disk?

Chris D

A CLV type (Constant Linear Velocity) will vary the RPM in
direct relation to where the head is reading, such that the
linear velocity of the track read, remains constant. IIRC,
a drive old enough to be 1X would be CLV.

There is much detail about basics like this online, the OP
should've done a Google search.
http://www.google.com/search?q=CDROM+CAV+CLV

 

[Mike Walsh]

Slower CD drives, up to about 16x, run at constant linear velocity. The RPM changes so that data is read at a constant bitrate anywhere on the disk.
Faster drives run at a constant RPM. A 50x drive turns at 10,000 RPM and reads at 50x at the outer edge of the disk but only 20x at the inner edge.

How can the inner edge of a disk be doing more revolutions per minute than
the outside of the disk? or is it that the speed varies as it reads
different parts of the disk?

Chris D

--

When replying by Email include NewSGrouP (case sensitive) in Subject

Mike Walsh
West Palm Beach, Florida, U.S.A.

 

[JK]

This makes me wonder why CDRs are written starting from the inside rather
than the outside? For disks that are only partially full, reading and writing
would be faster with a scheme starting from the outside of the disk. I guess
starting from the inside was chosen for compatibility with music CDs?

 

[Mike Walsh]

The original audio CD format specified either the standard size CD or a smaller size, which is rarely seen. By starting access at the center of the CD it is easy to read any size disk. When reading at constant linear velocity it doesn't make much difference whether you start at the inner or the outer edge. Sony and Philips obviously did not foresee 50x and faster drives when they released the specs.

This makes me wonder why CDRs are written starting from the inside rather
than the outside? For disks that are only partially full, reading and writing
would be faster with a scheme starting from the outside of the disk. I guess
starting from the inside was chosen for compatibility with music CDs?

--

When replying by Email include NewSGrouP (case sensitive) in Subject

Mike Walsh
West Palm Beach, Florida, U.S.A.

 

[DaveW]

Yes, that's the idea.

 

[DevilsPGD]

In message <[email protected]> Mike Walsh

The original audio CD format specified either the standard size CD or a smaller size, which is rarely seen. By starting access at the center of the CD it is easy to read any size disk. When reading at constant linear velocity it doesn't make much difference whether you start at the inner or the outer edge. Sony and Philips obviously did not foresee 50x and faster drives when they released the specs.

With the original spec in mind, it shouldn't be hard for CD mastering
software to take this into account.

It's been a while since I read up on CDFS, but it should be possible to
start the data track anywhere on the CD, shouldn't it? If you know up
front you're only planning to put 120MB on a CD, calculating and
creating an unused "track" taking up the innermost portion of the CD
would sound like a good idea, wouldn't it?

 

[CBFalconer]

Slower CD drives, up to about 16x, run at constant linear velocity.
The RPM changes so that data is read at a constant bitrate anywhere
on the disk. Faster drives run at a constant RPM. A 50x drive turns
at 10,000 RPM and reads at 50x at the outer edge of the disk but
only 20x at the inner edge.

Actually the thing that is being kept constant is linear length
traversed per bit, on both recording and reading. That means the
inner are has less data per revolution.

 

[kony]

In message <[email protected]> Mike Walsh


With the original spec in mind, it shouldn't be hard for CD mastering
software to take this into account.

It's been a while since I read up on CDFS, but it should be possible to
start the data track anywhere on the CD, shouldn't it? If you know up
front you're only planning to put 120MB on a CD, calculating and
creating an unused "track" taking up the innermost portion of the CD
would sound like a good idea, wouldn't it?

Data burnt at the slower speeds is more likely to be
readable with poor burner, media, or reader.

 

[DevilsPGD]

In message <[email protected]> kony

Data burnt at the slower speeds is more likely to be
readable with poor burner, media, or reader.

While true, I'm not sure what that has to do with what my post said at
all. My post addressed a method to place content on the actual CD to
increase read speed, I didn't speak to write speed at all.

 

[kony]

In message <[email protected]> kony


While true, I'm not sure what that has to do with what my post said at
all. My post addressed a method to place content on the actual CD to
increase read speed, I didn't speak to write speed at all.

Same difference, higher read speed makes it harder to read
(else what was the point?), though it would also be implied
that it was burnt faster too, all things being equal.

 

[DevilsPGD]

In message <[email protected]> kony

Same difference, higher read speed makes it harder to read
(else what was the point?), though it would also be implied
that it was burnt faster too, all things being equal.

My suggestion would actually increase the write time, possibly
substantially.

Personally, I tend to burn a CDR once, but read it more then once -- So
additional burn time isn't an issue if it saves me time every time I
read the CD down the road.

I don't really see higher read speed = harder to read as a
consideration. Or rather, that's not my problem.

If a CD reader can't keep up with the speed it chooses to use, it's
defective and the user should take it back to the retailer or the
manufacturer. Moreover, the reader can slow down. The reader cannot
fix a bad burn though, of course.

 

[kony]

In message <[email protected]> kony


My suggestion would actually increase the write time, possibly
substantially.

So is the goal running games from CD or what other use
requires utmost read speed at expense of much longer burn
time?

Personally, I tend to burn a CDR once, but read it more then once -- So
additional burn time isn't an issue if it saves me time every time I
read the CD down the road.

I don't really see higher read speed = harder to read as a
consideration. Or rather, that's not my problem.

If a CD reader can't keep up with the speed it chooses to use, it's
defective and the user should take it back to the retailer or the
manufacturer. Moreover, the reader can slow down. The reader cannot
fix a bad burn though, of course.

It's a good concept but these days with many readers being
nearly free after rebate, it's hardly worth the time or
money to get one replaced. Also you're ignoring the other
two causes, poor burning or media... A reader may work fine
but still struggle because the finished disc is very low
quality.

Readers may slow down, but often it's not just a linear
speed decrease, it slows down substantially... not sure to
what speed but i've noticed it may take much, much longer.

 

[DevilsPGD]

In message <[email protected]> kony

So is the goal running games from CD or what other use
requires utmost read speed at expense of much longer burn
time?

Not so much game play, but situations where you're copying a whole bunch
of data from CD to the system.

When you're going PC to PC installing patches, for instance, an extra 10
minutes burning one CDR means nothing if you can read 150MB from the CD
at 48X instead of 16X, this could easily save you 10 minutes per PC.

(I often build patches that copy from CD to HD first, then start
installing -- That way I only have to sit in front of the PC long enough
for the files to copy, I don't need to wait for the patch. Once I get a
few PCs down the line I can go back and check on the first few machines.

It's a good concept but these days with many readers being
nearly free after rebate, it's hardly worth the time or
money to get one replaced. Also you're ignoring the other
two causes, poor burning or media... A reader may work fine
but still struggle because the finished disc is very low
quality.

True, but poor burning can be handled, especially if you're building an
image for deployment rather then burning a few porn pictures for a buddy
(or some other single use case)

Readers may slow down, but often it's not just a linear
speed decrease, it slows down substantially... not sure to
what speed but i've noticed it may take much, much longer.

Yeah, makes sense.