Data Units

The way data units should be represented, according to IEEE 1541-2002

    Ever wonder why, when you buy a 4.7 GB blank DVD at a store, and then you put it in your computer and Windows or your DVD burning software says it's 4.37 GB, or some other much smaller number? Well it does have a little to do with part of the DVD being used as a file allocation table, and sectors forcing files to take up set amounts of space, and some parts of the DVD just not being burn-to-able by your DVD burner. But, all this would only reduce the size a little bit from the advertised size.

    Think the DVD makers are lying? Nope, Windows is lying. You may have heard that there are 1,024 bytes in a kilobyte. That is wrong. There are 1,024 bytes in a kibibyte, and 1,000 bytes in a kilobyte. So, when a DVD maker says 4.7 GB, or gigabytes, they mean 4,700,000,000 bytes. When Windows says 4.37 GB, it means to say 4.37 GiB, or gibibytes, which is about 4,700,000,000 bytes.

    Why Windows doesn't use the proper abbreviation, I don't know. This problem is becoming apparent in disk drive sizes and data transfers over the internet. As we get into terabytes, things will get more confusing for the common user, when space seems to just appear and disappear. So, until everybody starts following the standard, here a lookup table so that you know what to look out for.

  • 1 byte = 8 bits 


bit : b

  • kilobit : kb = 1,000 bits (10^3 bits)
  • megabit : Mb = 1,000,000 bits (10^6 bits)
  • gigabit : Gb = 1,000,000,000 bits (10^9 bits)
  • terabit : Tb = 1,000,000,000,000 bits (10^12 bits) 
  • kibibit : Kib = 1,024 bits (2^10 bits)
  • mebibit : Mib = 1,048,576 bits (2^20 bits)
  • gibibit : Gib = 1,073,741,824 bits (2^30 bits)
  • tebibit : Tib = 1,099,511,627,776 bits (2^40 bits)


byte: B

  • kilobyte : kB
  • megabyte : MB
  • gigabyte : GB
  • terabtye : TB 
  • kibibyte : KiB
  • mebibyte : MiB
  • gibibyte : GiB
  • tebibyte : TiB



  • * per second : *ps or */s



Note: it is in my experience that it is acceptable for 2 people to agree that when they say kilobyte, they mean it in the 1024 sense, before beginning a conversation that may include references to data unit degrees.