Effect on the disk system

For the system as a whole, ECS system action times were about evenly divided in the following groups:

• read and write files
• send and receive events
• call and return from subprocesses
• miscellaneous

If we assume that most of the file and event channel activity was on behalf of the disk system (which we suspected but never attempted to prove), and observe that the disk system rarely made subprocess calls, then we see that a substantial portion of the disk system time is spent on files and event channels. Most of the disk system's file actions were directed to a single file which contained its global data base. If this file were made directly accessable, great saving would result. (The disk system was coded so that only a re-assembly was necessary to take advantage of the direct access.) This we expected to reduce most disk system ECS file action times by about 90 about 50 18 milliseconds of CPU time required by the disk system for a single block transfer, 12 milliseconds are consumed in ECS system actions. The above figures suggest that Direct ECS access and fast actions will reduce this to about one third, or 4 milliseconds. Thus the per block overhead for disk transfers would reduce to about 10 milliseconds, for multiblock transfers.