Typical storage capacities by Matt Ottewill - Sept 2010

"Data capacity" is a measure of the capacity of storage and memory devices such as memory sticks, hard drives, RAM, ROM and optical discs. Like Moores Law for CPUs, the storage capacity to cost ratio doubles approximately every 2 years.

Here are some common devices and their capacities ...

Device Image Typical capacity Comments
RAM RAM 500Mb-8Gb  
SSD (Solid State drive)   300-500Gb Flash Ram storage. Faster than magnetic HD's, and use less energy and produce less heat, but have smaller capacities and are expensive.
Hard disk drive (magnetic) 500Gb - 4Tb Hard disc drives are discussed here
USB memory sticks 2-64Gb Flash RAM
Floppy disc 3.5 inch DS/DD 800Kb Double sided / double density
Floppy disc 3.5 inch HD 1.4Mb High density
Compact disc - CD disc 650-740Mb

This can be extended up to 800Mb through a process known as "over-burning", though there is no guarantee that all CD drives will be able to access the extra data.

NOTE: Some of the different compact disc standards are discussed in our article on CD mastering.

Compact disc - CDROM 650Mb (+ 90Mb error correction data)

If a blank disc is used to backup computer files in data, or CD-ROM format, approximately 90Mb of capacity is used for error correction purposes, leaving 650Mb for data.

Compact disc - Red book audio 740Mb (74 minutes)

If a computer CD-R blank disc is used to create a so called "Red book" audio disc, suitable for domestic audio players, all 740Mb of capacity can be used for music. Error correction is handled by the players themselves.

If the files are burnt in data, or CD-ROM format (as .wav, .aiff, or .mpg etc) capacity is as CD-ROM (650Mb).

NOTE: Computers CD-R drives can create red book audio CDs from computer CD-R blank discs (avoid CD-RW for this purpose). Domestic audio CD recorders use pre-formatted CD-Audio discs.

DVD (Digital Versatile Disc) 4.37-15.9Gb Click here for a full overview of the DVD format
Blu-Ray Single layer = 25Gb, Dual layer = 50Gb Adopted for HD video delivery and 3rd gen gaming platforms, but has not taken off for computer storage/backup yet.