Capacity of a cd

[JPaul]

Velocity CAV v CLV

CD-ROM drives that are over 16x will generally have max written next to it. When max is written next to the speed or on the drive, this indicates that the CD-ROM uses CAV, or Constant Angular Velocity, to access the data on the CD. Originally, CD-ROM drives utilized CLV, or Constant Linear Velocity, where the information was accessed slower / faster by adjusting the speed of the motor which allows the data to be transferred at a steady flow.

With CAV, the CD rotates at a constant speed without adjusting when at a different location on the CD, which means a 32x speed CD-ROM, for example, will be able to access the data 32x on the outside layer, however, when approaching the middle of the CD-ROM drive, the access speed can decrease close to 20x.

http://www.computerhope.com/issues/ch000219.htm

[JPaul]

Constant Linear Velocity (CLV) is the principle by which data is read from a CD-ROM. This principal states that the read head must interact with the data track at a constant rate, whether it is accessing data from the inner or outermost portions of the disc. This is affected by varying the rotation speed of the disc, from 500 rpm at the center, to 200 rpm at the outside. In a music CD, data is read sequentially, so rotation speed is not an issue. The CD-ROM, on the other hand, must read in random patterns, which necessitates constantly shifting rotation speeds. Pauses in the read function are audible, and some of the faster drives can be quite



That is where i got that information from, if its the same speed Jpaul then what would that speed be?

See my last, I think CAV has superceded CLV in newer drives.

I think it depends on the max speed of the CD Rom and the disk being used. I'll try to find out what speeds they are talking about.

[JPaul]

Feck, there P-CAV (partial) and Z-CLV (zoned) as well.

http://www.cdspeed2000.com/go.php3?l...q_general.html

[scribblec]

looks very confusing

[JPaul]

It certainly appears to be.

I would just rip stuff from the "howthingswork" site. There's actually quite a lot there.

[thewizeard]

...but there is a special quantum algorithm, which saves you doing all of that...


edit:- http://www.filesharingtalk.com/vb3/t112206.html

[ilw]

re destructive interference

the data is stored in pits and non-pits (land?)
the laser is shone onto the track and is reflected back either from hte pit or land. Laser light is coherent ie all in phase. the distance between the laser and track is set up so that reflections from a non-pit are in phase with the incident light. The depth of a pit is set up to be 1/4 wavelength of the laser light so for the light to go down into the pit and come out again it will travel an extra 1/2 a wavelength and be 180degrees out of phase with the incident light and this causes light reflected from a pit to destructively interfere.
Therefore to the sensor bright = land and dark = pit.
Pretty bad explanation, but it should give you info you can google

[scribblec]

thanks alot guys ended up getting an A on the coursework and probably due to the extra topics brought up for me to include, the teacher said it was one of the most interesting he had read this year

[thewizeard]

haha .. nice one scribblec