Memory cycle time (Memory) over time
Time for one complete memory read/write cycle. The fundamental timing unit of a core-memory machine, whose instruction times are whole multiples of it.
- Device scope
- memory
- Method
- Nominal cycle time
- Plotted in
- second
Chart
3 figures from 3 machines, spanning 1964 to 1981. The lowest memory cycle time here is 250 ns (BBC Micro Model B, 1981) and the highest is 2.0 µs (IBM System/360 Model 50, 1964). That is a range of about 8.0× within one comparability group; the figures are plotted in s. Points use the release date of the machine the figure belongs to. The table below lists absent figures with their recorded reasons.
Data
| Machine | Released | Figure | Confidence | Sources |
|---|---|---|---|---|
| IBM System/360 Model 50 IBM 2050F Main Storage | April 1964 | 2.0 µs A main-storage read/write cycle; the shorter ROS and local-storage cycles are separate. | Vendor-rated | |
| IBM Personal Computer 5150 | August 1981 | 840 ns One processor generated memory read or write cycle with Ready inactive. | Vendor-rated | |
| BBC Micro Model B | December 1981 | 250 ns One shared-RAM access; control alternates between the processor and CRTC. | Vendor-rated |
Why this chart holds one group only
Every point on a chart is implicitly compared with every other point on it. This chart uses one comparability group: one metric, one device scope, one method . There is no chart of all clock frequencies over time because they are not one quantity.
Points use the release date of the machine a figure belongs to, including figures recorded against a part. A release date applies only to a machine that shipped. What this metric measures.