3.3.3 - Bits, bytes and decimal prefixes

Bits and bytes

A bit is the smallest unit of binary information, and a byte groups eight bits together.

The pattern 00101101 contains eight bits, so it occupies one byte. A byte has 256 possible patterns because every one of its eight positions has two possibilities: $2^8=256$. The possible unsigned number values are 0–255, which is 256 values including zero.

To convert bytes to bits, multiply by 8. A 12-byte field contains $12\times8=96$ bits. To convert bits to bytes, divide by 8. A 96-bit field occupies $96\div8=12$ bytes. These conversions describe the same amount of information; they do not compress it.

The letter case matters. 40 Mb and 40 MB differ by a factor of eight. Write the unit with every result so the reader knows which quantity you mean. Later image and sound formulas produce bits first, so the division by eight is a separate step when bytes are requested.

Decimal storage prefixes

Decimal prefixes let us express large byte quantities without long strings of zeros.