The logical organization of the PB 440 microprogrammable computer
E. O. Boutwell, E. A. Hoskinson · 1963
The principal classifying feature of the PB 440 is its microprogrammed character. Like other so-called "general purpose" computers, it derives control from a program of instructions or orders which has been previously prepared and stored within the computer memory. Unlike most general purpose computers, however, the PB 440 programmer is permitted to direct the computer at a more basic level of control by logically manipulating the contents of individual registers and flip flops.