Mass memory in computer systems

Mass memory has three distinct uses in a computer system. Each places distinct requirements on the technology. This paper gives a personal estimate of the requirements for each use in the next five years. 1) A mass memory may be used as a cheaper extension of main memory. For this use, cycle time must be
\leq 10 \mu
s, capacity 1-8 million bytes, addressed to the word, read-write, and cost per bit must be less than 1/4 that of main memory. 2) A mass memory may be used for residence of the control program and compilers. For this use, cycle time must be
\leq 10 \mu
s, block transfer rate ≥ 1 million byte/s, capacity 8-32 million bytes. It may be read-only (if easily changeable) and addressed only in blocks. Cost per bit must be less than 1/10 that of main memory. 3) A mass memory may be used for storage of an on-line data base. Such a memory must have >500 million bytes capacity, a cycle time <100 ms, may be block addressed, may be read-only for some uses but not most. Cost must be <0.004 cent/bit to compete with today's technologies. Special memory properties, such as content-addressing, distributed logic, etc., will not redeem a memory that is not competitive on cycle time, capacity, block transfer rate, and cost.