CD ROM Sector Information and Capacity

written by: Terry McLean; article published: year 2006, month 11;

In: Root » Computers and technology » Storage devices

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Because a typical disc can hold a maximum of 74 minutes of data, and each second contains 75 blocks of 2,048 bytes each, you can calculate the absolute maximum storage capacity of a CD-ROM at 681,984,000 bytesrounded as 682MB (megabytes) or 650MiB (mebibytes). The table below shows the structure and layout of each sector on a CD-ROM on which data is stored.

CD-ROM Sector Information and Capacity
Each Data Sector (Mode 1): 74-Minute 80-Minute
------------------------------------------------------------------------------------
Q+P parity bytes 784 784
Subcode bytes 98 98
------------------------------------------------------------------------------------
Sync bytes 12 12
Header bytes 8 8
ECC/EDC bytes 284 284
------------------------------------------------------------------------------------
Data bytes 2,048 2,048
------------------------------------------------------------------------------------
Bytes/sector RAW (unencoded) 3,234 3,234
Actual CD-ROM Data Capacity:
------------------------------------------------------------------------------------
B 681,984,000 737,280,000
KiB 666,000 720,000
KB 681,984 737,280
MiB 650.39 703.13
MB 681.98 737.28
B = Byte (8 bits)
KB = Kilobyte (1,000 bytes)
KiB = Kibibyte (1,024 bytes)
MB = Megabyte (1,000,000 bytes)
MiB = Mebibyte (1,048,576 bytes)
ECC = Error correction code
EDC = Error detection code


This information assumes the data is stored in Mode 1 format, which is used on virtually all data discs.

With data sectors, you can see that out of 3,234 actual bytes per sector, only 2,048 are actual CD-ROM user data. Most of the 1,186 other bytes are used for the intensive error detection and correction schemes to ensure error-free performance.

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