I was looking into PHP’s pack function. I noticed this in the implemented formats list:
|h||Hex string, low nibble first|
|H||Hex string, high nibble first|
“In computing, a nibble (often nybble or even nyble to simulate the spelling of byte) is a four-bit aggregation, or half an octet. As a nibble contains 4 bits, there are sixteen (24) possible values, so a nibble corresponds to a single hexadecimal digit (thus, it is often referred to as a “hex digit” or “hexit”).” – http://en.wikipedia.org/wiki/Nibble
1 nibble is 4 bits two nibbles make a byte (bite, to keep the metaphore going).
So what about high and low nibbles you might wonder. I found some clear information on a webpage about converting between decimal and binary formats.
“There is a simpler way to convert bytes back and forth between binary and decimal. The byte can split into two four-bit halves, each half called a nibble. Memorize the decimal values for the high nibble (they’re just the multiples of 16). The low nibble is trivial. Every number between 0 and 255 is the sum of one of the high nibble values and one of the low nibble values. Write the high nibble next to the low nibble, and you have the byte value in binary. Conversely, an eight-bit binary byte can be split in half, each nibble converted to decimal and two decimal numbers added together.” – Binary Arithmetic (at the bottom of the page there is a nice visual)