Operation checking system for data storage and processing machines

926,181. Digital electric calculating. INTERNATIONAL BUSINESS MACHINES CORPORATION. May 9, 1960 [June 11, 1959 (3)], No. 16245/60. Class 106 (1). In a stored programme general purpose computor an instruction word may call up at least a part of a further word, named a control word, in order to complete the information necessary that the operation specified by the instruction word be performed. The main store is a magnetic core matrix into which data from peripheral devices such as magnetic tape stores, punched cards or tape may be read in one half-word at a time and from which data being processed including instruction words is read into three registers having interchangeable functions but of which two may be combined to form upper and lower accumulators. The computer is asynchronous, the completion of one operation leading to the read-out of the instruction word for the next operation from an address specified by an instruction counter. In the main store each word comprises ten alpha-numeric, six-bit (plus parity bit) characters, each character comprising four numeric and two zone bits. An instruction or control word comprises sixteen four-bit numeric characters, compressed to fifteen by limitation of variables and stored as ten six-bit characters by utilizing the zone bits of two characters of a storage word to specify one character of an instruction or control word. Thus the zone bits of characters 0 and 1 of a storage word represent the eleventh character of an instruction and are staticized as such in a register. A data word may be of up to ten characters overlapping two adjacent storage words, and if such a condition exists, known as a split-field, an operation is preceded by assembly of the required data word in one of the registers. A data word may be distinguished by its state which is on if a bit is present in the first zone position of the character 8, off otherwise. The machine is controlled by timers to each of which is allotted a fixed number of time intervals not all of which are used for any particular operations. Thus the arithmetic timer has 28 " times " but in the add operation without split-field only times 5, possibly 6, and 24 are used. The timers jump directly to the times used in the operation being performed. Instructions: format and codes.-An instruction word which is one of the specific types listed below, is in the form of an operation code (two characters), modifier (one character), control (four characters), operand (four chara