We said that because simultaneous transfer is possible, a memory with many wires
has high performance. More important: an interface that has more wires will transfer
data at a higher rate. That is, a memory system that uses a word size of K will have
higher performance than a memory system that uses a word size less than K. Of course,
increasing the word size increases the cost of the hardware.
What word size should an architect choose? The question is complicated by
several factors. First, because memory is used to store data, the word size should accommodate
common data values (e.g., the word should be large enough to hold an integer).
Second, because memory is used to store programs, the word size should accommodate
frequently used instructions. Third, because parallel hardware takes space
and adds to the economic cost, the word size is chosen as a compromise between performance
and various costs. For example, some architects have chosen a word size of
thirty-two bits; others have selected sixty-four.
In most cases, an architect designs all parts of a computer system to work together.
Thus, if an architect chooses a memory word size equal to thirty-two bits, the architect
will make a standard integer and a single-precision floating point value each occupy
thirty-two bits. As a result, a computer system is often characterized by stating the
word size (e.g., a thirty-two bit processor).