Page:CTSS programmer's guide.djvu/19

 first pilot version of the time-sharing system is expected to be completed by summer, 1963. In fall, 1963, the addition of an IBM 7320 moderate-speed drum should further increase system performance by allowing somewhat faster secondary memory access and transmission speeds for swapping programs in and out of core memory, although the drum memory capacity is limited. At this time the general performance of the 7090 will be improved by upgrading it to a 7094 Model 1.

To implement effective operation of a pilot time-sharing system, the initial 16 Teletype consoles have been deployed as follows: two consoles for the Center system programming staff to assist in implementation and evaluation; one in the programmer consulting office to allow rapid assistance to users in the location of errors; one with the Center keypunch operators for service keypunching directly into the disk memory; one for the 7090 computer console operator; one for the 7090 tape-mount operator; one in Professor Minsky's research group for their applications and system evaluation; one in Professor Corbató's office for analysis, monitoring, demonstrations, and programming purposes; one more remotely located at Professor Miller's Civil Engineering Computation installation; and seven in an open pool for general time-sharing users at the Center.

One of the principal design features of the pilot system is that most older pre-time-sharing systems may be operated in the role of a background program simultaneously with the foreground time-sharing console system (memo CC-202-1). Because of the weakness of input-output memory protection in the 7090, it was necessary to develop an intricate input-output analyzer-monitor program for safe operation of older programs which had been developed without time-sharing in mind. Besides easing the programming transition problems of changing from batch processing to time-sharing techniques, this compatibility feature eliminates the necessity for immediately satisfying all of the Center's 400 research users (and a similar number of student users) with the initial version of the time-sharing system.

To achieve programming compatibility, the time-sharing system uses the same programming languages normally available in the major Center 5