Uses of Bitwise Logic

The first six bits of the instruction (the opcode) specify the machine operation. (Sometimes a secondary opcode is needed). The opcode also determines how the rest of the instruction is laid out. A human needs to look at documentation to figure out the bit fields of an instruction and what they mean. The MIPS processor does this automatically.

Recall (from the second chapter) the fourth advantage of binary:

1. Simple; easy to build.
2. Unambiguous signals (hence noise immunity).
3. Flawless copies can be made.
4. Anything that can be represented with some sort of pattern can be represented with patterns of bits.

Most computers have built-in integer arithmetic operations and often built-in floating point operations. But computers are used for much more than numbers! Bit patterns are used to represent very many things. Bitwise logic is needed when computing with bit patterns in all their various uses.

For example, a document created with a word processor has font and formatting information embedded within it. The information is encoded with bit patterns in ways specific to each word processor family. A word processor program must use bitwise operations to process these codes.