No. 1 ESS ADF: Message Store - A Disk Message System

An essential element of the No. 1 ESS A D F store and forward data handling system is an economical, nondestructive readout, bulk m e m - ory with an average thruput of 153 kb/s. Core and ferrite sheet memories meet the access requirement, but their costs and destructive readout make them less attractive than the slower access disk or drum large capacity memories. 1 In a study conducted to select a memory file that would best fit the A D F application, the following requirements were established for the memory: (i) present commercial production and indication of continuing supply over the years, (ii) performance over the expected 40-year life of the system with minimum downtime and repair cost, {Hi) fixed head/track access with a minimum of mechanical equipment, and (iv) capacity of at least 50 megabits. The file selected, a Burroughs Corporation model BC475 Disk File, has a fixed head/track access scheme, a capacity of 60 megabits, and an average access time of 20 milliseconds (1/2 of a revolution). 2887