How much information can actually be stored on CD-R
The amount of information that can be written is determined by the disc’s recording capacity as well as the physical and logical formats used.
Each of the five main CD physical formats devotes a different amount of space to user data (audio = 2,352 bytes/block, CD-ROM Mode 1 = 2,048 bytes/block, CD-ROM Mode 2 = 2,336/bytes/block, XA Form 1 = 2,048 bytes/block, XA Form 2 = 2,324 bytes/block). For any given data format disc capacity can be calculated by multiplying the appropriate user data area size by the CD data transfer rate of 75 blocks per second by 60 seconds by the minute size of disc. For example, a 80 minute disc written in CD-ROM Mode 1 format: user data area of 2048 bytes/block x 75 blocks/second = 153,600 bytes/second x 60 seconds = 9,216,000 bytes/minute x 80 minutes = 737,280,000 bytes. This rounds to roughly 700 MB (dividing by 1,024 to convert into KB and again by 1,024 to convert into MB). It should be noted, however, that in the real world capacity can vary slightly among discs from different media manufacturers.
So typically a standard 700MB CD-R derives its listed capacity from a 2048 bytes/sector calculation. If the same disc is written in Mode 2 the capacity will have increased to 801 MB
Size of a disc image
The generally used images for CD's contain besides the actual data that are to be written to CD, also a substantial amount of overhead describing the lay out of the data on disc and many more characteristics to arrive at a 1:1 copy of the original
Especially CloneCD goes to great length to describe the data in detail. Both the CD and SUB files are very important in this respect.
You will notice that the images concerned, often are considerably larer than the advertised capacity of the CD-R
Do not worry because the image has been obtained from a CD-R with a fully normal capacity, sometimes not exceeding 650 MB
So the obtained image will cettainly fir the blank media you are going to use
If you mount the image you can check yourself what the total size of the files is going to be
Last edited by gazo; 28th October 2010 at 14:20.
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