Electronic data processing machine

800,505. Digital electric calculating-apparatus; electric digital-data-storage apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. March 18, 1955 [March 22, 1954], No. 7918/55. Class 106 (1). Electronic data processing apparatus includes input and output devices interconnected by a computer which employs variable length words, the lengths being demarcated by special coded characters. General. The electronic computer illustrated in Figs. 1a and 1b comprises a C.R.T. memory M, an accumulator including a C.R.T. store AS, and input/output magnetic tape units T. Words comprise a variable number of coded characters each represented by seven bits, Fig. 1c, comprising four numerical bits 1, 2, 4, 8, two zone bits A, B and a redundancy check bit C such as to make the total of " 1 "s in a character always odd. Numbers are in decimal form and have their digits represented in the excess-three code, the zone bits being "0." Words are separated by field marks " +," "-," Fig. 1c, the mark " - " being used only for numbers stored in the memory to indicate a negative sign. In the accumulator store, a negative sign is indicated by numerical " 9 " with " + " field mark zone digits. The field marks and other special characters are detected by recognition circuits CRC associated with two characters registers CR1, CR2, Fig. 1b, which receive characters as they are read out from the memory or accumulator store via main bus MB or accumulator storage bus AB, and also form a buffer between the memory and the tape units. The memory comprises 50 pairs of C.R.T.s; a pair is selected by unit selector US and a " left " or " right " C.R.T. of this pair by memory left/right control MC. The beam in the selected C.R.T. may be deflected to one of 100 character positions by memory deflection circuits MD. The circuits US, MC, MD are controlled by the portions indicated of a 4-decimal-digit address through memory switch MS. A word location is given by the address of the "right-hand " field mark (the one with the higher address number); e.g. the address of the number 123, 456, Fig. 1h, is 0037. Transfer to and from tape (writing and reading) is effected in the order of increasing address numbers (" left to right "), but transfer between the memory and the accumulator is effected in the reverse order (" right to left "). The accumulator store AS, which normally stores one word only, comprises a single C.R.T. having 100 character positions selected by deflection circuits ASD controlled by 2-di