FIGURE 7 Block diagram of the IBM 360/44 system at Yale.
3. Software System
The general-purpose multiprogramming operating system is a multilevel priority system designed to provide access to the system simultaneously by an, in principle, unlimited number of users, each with unique priority. Unlimited means that there is no arbitrary restriction on the number of users; the nth user can always get access if the facilities his particular job requires are not already in use. Two types of user are recognized by the system: The basic unit of execution is the logical user, or task. Each logical user has a unique priority level. Switching between users is carried out as a response to I/O, timer, or external interrupts, at which time the highest priority user in a position to execute gains control of the central processor. The basic unit of memory protection is the physical user, composed of one or more logical users engaged in a common cause. Physical users correspond to real people doing independent work simultaneously. By dividing his work up among a group of logical users, a person may take advantage of the parallel processing capabilities of the system in a natural way. Since logical users within a physical user are not memory-protected against each other, they may communicate rapidly, at full machine speed. Communication between different physical users is also possible, via real or simulated I/O devices. While this system by no means guarantees execution time to any but the highest priority user, it is adequate in a single-experiment environment. The assumption is that the experimenter, who has actual control of the computer at all times, loads his logical users in the order in which he requires their priorities. Following this, other users load their jobs, getting whatever memory and I/O facilities remain. The amount of processor time available to the other users varies inversely with the experimenter's counting rate and the amount of processing he does on his data. In most experiments, the experimenter uses significantly less than 50 percent of the processor time simply because those experiments requiring the sophistication of the computer also have rather low counting rates. A priori, it is estimated that the simple priority algorithm described above is not only adequate but pays a dividend in terms of reduced system overhead time as compared to a more elaborate algorithm. It also guarantees that no data will be lost due to the lower priority users being in the machine.
In general the new system will provide all the facilities of 44PS within the multiprogramming framework, including execution of the Fortran compiler simultaneously with data acquisition.
| TABLE 4 | ||
| The Basic System | ||
| CPU: with 128k-byte memory, 1-µsec registers,external interrupts, floating point, onehigh-speed multiplex channel, one low-speedmultiplex channel, and one single-diskstorage drive | $291,280.00 | |
| Standard I/O gear: with 128k-byte memory, 1-µsec registers,external interrupts, floating point, onehigh-speed multiplex channel, one low-speedmultiplex channel, and one single-diskstorage drive | 164,259.00 | |
| Data-acquisition and display subsystem[C]: | ||
| Display system (RPQ on 1827) withfunction keyboard and light pen | 19,000.00 | |
| 2972-VII Scientific Interface and ControlUnit (front end) | 40,000.00 | |
| 6 LeCroy model 157M general-purpose registersand ADC interface to 2972, as designed forMaryland | 5,950.00 | |
| 2 LeCroy model 150B scaler banks (each containseight 15-bit scalers with separate inhibit,strobe, and reset, as modified for Maryland) | 3,900.00 | |
| 2 LeCroy interfaces to connect model 150Bto 2972 | 2,000.00 | |
| 4 Northern Scientific 4096-channel ADC's | 8,800.00 | |
| Data-acquisition and display subtotal | 79,650.00 | |
| TOTAL | $535,189.00 | |
| [C] As previously stated, the data-acquisition and display subsystem intalled at Yale is the laboratory prototype of the IBM equipment, for which Yale paid only a nominal sum. | ||
| TABLE 5 | ||
| Additional Items Needed to Make a System Identical to the Yale System | ||
| CPU and peripherals: additional high-speed multiplex channel withextra subchannel, high-speed (1/4 µsec)general registers, additional single-diskstorage drive, memory protect, additionaltape drive (240IV),[D]1627 (Calcomp) plotterand adapter, keypunch, six additional diskcartridges | $114,316.00 | |
| Data-acquisition subsystem | ||
| 2 additional Northern Scientific 4k ADC's | 4,400.00 | |
| 2 additional LeCroy 157M registers | 1,400.00 | |
| Costs of extras | 120,116.00 | |
| Grand total for basic system | 535,189.00 | |
| Cost to copy the Yale system | TOTAL | $655,305.00 |
| [D] About $20,000 can be saved on tape drives by using the slowest ones (30k bytes/sec) rather than the 120k bytes/sec units shown here. | ||