Data in memory

Values contained in memory are usually accessible as bytes (8 bits), short words (16 bits), long words (32 bits), or double words (64 bits). Generally, specific instruction codes handle exactly one type of data. There may also be some that handle data as signed or unsigned values. A signed value might result in sign-bit extension when it is loaded into a register, whereas an unsigned value would force the unused bits to be set to zero.

Values that are stored in memory have two different forms they can follow. The most common is the "Big-Endian" scheme; that is, data needing more than one byte will have the high-order bytes stored first. For example, the long hex number 0x12345678 would be stored, on a SPARC system (a Big-Endian system), as the following sequence of bytes.

0x12 0x34 0x56 0x78

Some architectures, notably the common Intel chips, use the reverse method. This would result in the sequence:

0x78 0x56 0x34 0x12

when scanning memory from a low to a high address.