Jun 07, 2012 01:20 PM
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A CD-ROM sector contains 2, 352 bytes, divided into 98 24-byte frames. Unlike a music CD, a CD-ROM cannot rely on error concealment by interpolation, and therefore requires a higher reliability of the retrieved data. In order to achieve improved error correction and detection, a CD-ROM has a third layer of Reed–Solomon error correction. [ 4 ] A Mode-1 CD-ROM, which has the full three layers of error correction data, contains a net 2, 048 bytes of the available 2, 352 per sector. In a Mode-2 CD-ROM, which is mostly used for video files, there are 2, 336 user-available bytes per sector. The net byte rate of a Mode-1 CD-ROM, based on comparison to CDDA audio standards, is 44100 Hz × 16 bits/sample × 2 channels × 2, 048 / 2, 352 /8= 153.6 kB/s= 150 KiB/s. The playing time is 74 minutes, or 4, 440 seconds, so that the net capacity of a Mode-1 CD-ROM is 682 MB or, equivalently, 650 MiB.
A 1× speed CD drive reads 75 consecutive sectors per second.
CD sector contents
A standard 74 min. CD contains 333, 000 blocks or sectors.Each sector is 2, 352 bytes, and contains 2, 048 bytes of PC(mode 1) data, 2, 336 bytes of PSX/VCD(mode 2) data, or 2, 352 bytes of audio.The difference between sector size and data content are the header information and the error-correcting codes, that are big for data(high precision required), small for VCD(standard for video) and none for audio. Note that all of these, including audio, still benefit from a lower layer of error correction at a sub-sector level.If extracting the disc in raw format(standard for creating images) always extract 2, 352 bytes per sector, not 2, 048/2, 336/2, 352 bytes depending on data type(basically, extracting the whole sector).
This fact has two main consequences: Recording data CDs at very high speed(40×) can be done without losing information. However, as audio CDs do not contain a third layer of error-correcting codes, recording these at high speed may result in more unrecoverable errors or'clicks' in the audio.On a 74 minute CD, one can fit larger images using raw mode, up to 333, 000 × 2, 352= 783, 216, 000 bytes(~747 MiB). This is the upper limit for raw images created on a 74 min or~650 MiB Red Book CD. The 14.8% increase is due to the discarding of error correction data. The sync pattern for Mode 1 CD [ 3 ] An image size is always a multiple of 2, 352 bytes(the size of a block) when extracting in raw mode. [ 5 ]
