synchronous computer[′siŋ·krə·nəs kəm′pyüd·ər]
a digital computer in which a control device determines the moments at which the performance of an operation begins and ends. The time allotted for the execution of an operation is calculated in advance, when the machine is designed. In the simplest case, the same time interval is used for the execution of all operations; this interval corresponds to the longest operation. In the general case, separate groups are formed of operations with approximately the same duration. For each group the maximum time to complete an operation is calculated, and corresponding cycles of the machine’s operation are established.
Since the cycles of synchronous computers are calculated on the basis of the longest elementary operation, the overall speed of such a machine is lower than the speed of a similar asynchronous computer. Synchronous computers, however, are simpler in design and circuitry, and consequently are easier to design, set up, and operate.
Most digital computers make use of both synchronous and asynchronous timing. In particular, the central processor may operate synchronously, and the peripheral asynchronously, because the latter coordinate the operation of the fast electronic logic elements with that of the slow electromechanical equipment. The operation of a peripheral is initiated by signals from the central processor and is carried out asynchronously. When the peripheral completes its work, an appropriate signal is sent to the central processor, which continues its work on the basis of synchronouos timing.