Design Considerations for a Semipermanent Optical Memory

The increased computational capabilities of modern day computers are accompanied by a sharply increased need for a semipermanent memory to store their base programs. The capacity requirements for a given base program memory generally increase as fast or perhaps faster than the computational complexity of the computer increases. Along with the increased capacity, the next generations of memories must have increased speed capabilities since the speed of the program memory generally controls the overall computer processing speed. Ideally, a program memory should have a random access capability to each instruction or to each group of instructions if the instructions can be suitably grouped. If individual instructions are accessed in one memory cycle, the speed of the program memory has to match the rate at which the desired instructions have to be made available to the logic or processor frame. If, however, a group of instructions can be obtained in one access 1267 1268 T H E BELL SYSTEM T E C H N I C A L J O U R N A L , J U L Y - A U G U S T 1907