Data Storage and Compression

//The units go up in 1024s

Cambridge uses the 'bi' units, which are powers of 2. Learn the ladder in order.

8 bits            = 1 byte
1024 bytes        = 1 kibibyte  (KiB)
1024 KiB          = 1 mebibyte  (MiB)
1024 MiB          = 1 gibibyte  (GiB)
1024 GiB          = 1 tebibyte  (TiB)
1024 TiB          = 1 pebibyte  (PiB)
1024 PiB          = 1 exbibyte  (EiB)

//Run-length encoding, worked

RLE is lossless: you can rebuild the original exactly. It only helps when there are long runs of the same value — on a noisy photo it can even make the file bigger.

Original:  w w w w w b b w w w
RLE:       5w 2b 3w

10 items -> 6 items, and no information lost.

//Choosing lossy or lossless

Lossy (JPEG, MP3) is fine for photos and music, because the removed detail is hard for a human to notice. Lossless (PNG, ZIP) must be used where every bit matters: text documents, spreadsheets, program files, medical scans.

KEY TERMS

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