1987
From the Directors Keyboard
by Bob Graham
In the late '70s and early '80s, the effect of response time of a terminal connected to the mainframe computer, when a programmer was working in an interactive environment, began to be understood. Several experiments were conducted and the results were published in the early '80s. The bottom line of these studies was that maximum "people" efficiency was achieved if sub-second response was maintained - meaning that the computer terminal response time was kept below one second.
Psychologist got into the act to explain what was occurring. Basically their explanation is this: as you approach performing a function in an interactive environment, you develop a plan in your mind of the steps you are going to go through. As you execute this sequence of steps, as long as the computer responds to each of your actions in 0.5 to 0.7 seconds, you will move smoothly from step to step, right to the completion of your planned action. If the computer responds in say 1.5 seconds, your concentration will be periodically broken and you will have to rethink the the process you had planned, causing even more of a delay. As the computer response increases, this need to "rethink" occurs more frequently, extending the total task time even more.
At the same time that this body of knowledge was being understood, the PC was evolving. The first machines, with their two diskette drives, were to be replaced with PC's with a hard disk. This made them faster and more efficient, making better use of the "people" time - and for a while were the "standard" to be ordered. Now, as speed of the AT is being understood, the relationship between PC speed and the users efficiency can better understood through the studies made on the mainframes. This knowledge can be used, in many cases, to present a business case for an "AT" class machine.
Now the "standard" PC has become the PS/2 Model 50, to a great extent because of its response time and resulting "people" efficiency.
02/22/99
The conclusions of this study are still valid today.
Today's PC environment with the point and click construct and Graphical User Interface (GUI) environment require a faster computer. Those designing and developing graphical applications require the fastest possible computer and also dictates larger memory and greater disk storage.
The information contained in the IBM study can still be used today to develop a business case for faster PCs.