previous | contents | next

Chapter 5 ½ Function and Performance 41

scientific computers as separate input/output control (either Kio or Pio), for it was realized that there were also demands on input/output for scientific calculation. Thus the bifurcation was temporarily halted.

The specialization to characters as a basic type (as opposed to long words) was already present in the IBM 702 but did not have its effect until 5 years later with the development of the IBM 1401, The latter machine was adapted to business, both in being character-based and in being small enough that small businesses could afford it. It was extremely successful (many thousands were produced) and certainly represents a successful functional specialization for business However, it is interesting that the specialization has not been maintained, for the IBM System/360 (Chaps. 40, 41, 51, and 52) is again a single machine, although it has in essence two internal ISPs, one centered around characters and the other around floating-point data-types, that is, a business and a scientific specialization residing side by side.1

Manufacturing Control

The function of computers in both the manufacturing and the commercial environments has evolved from simple record keeping to direct online human control. Process-control, aerospace, and laboratory instrument-control computers have evolved from their initial use in assisting human operators (controllers) with data logging and alarm condition monitoring to full control of processes with either human or second-computer backup. The structure of the computer and the control task varies widely depending on whether it is a continuous process (e.g., refinery, rolling mill) or a discrete process (e.g., warehouse, automotive, appliance manufacturing). The role of the computer is to act as a sophisticated control (K) in some larger physical process, and thus it plays a subordinate role. The computers' relatively late arrival in this role was due to the high cost and unreliability of early computers, as well as to the Lack of necessary interface equipment.

The functional specialization is seen most strongly in the word size, which reflects the appropriate numerical data-type. The numbers used in control processes are generated by physical devices and are rarely better than 0.1 percent accurate. Since elaborate arithmetic calculations are not called for, the numbers, and hence the word size, can be around 12 bits. Most control computers have been 8 to 18 bits per word. A second specialization, again reflecting appropriate data-types, is that all control computers are binary and have boolean operations. This arises because many of the external conditions to be sensed and effected are binary in nature.

About the only other functional specialization of control computers is the interrupt2 capability to allow them to respond to many potentially concurrent external conditions in real time. This provides overlap of internal and external processing. This is another possible example of functional specialization leading to reunification rather than divergence, for it has again been widely accepted that all general-purpose computers must have good interrupt capabilities. However, in actuality, interrupts, though not existing in early computers, were developed to obtain good input/output facilities, not for control computers.

Communications, Office, and Publication

The functional specialization of communication could be taken as a subfunction of a control computer. The function is mainly to behave as a switch. In a message-switching application the computer transfers messages from terminals (and links) into - primary (and sometimes secondary) memories and then transfers them to other terminals (and links). In message switching, messages are first stored and then forwarded, The computer in a telephone exchange functions as a very sophisticated switch control. Here the computer reads the off-the-hook signal, detects the dialed numbers, rings the dialed parties, and finally sets the switches to connect the telephones together. In some instances, when it answers information inquiries about new telephone numbers or reroutes calls to other phones, it functions as a memory. Thus a communications computer is functionally a switch or a control for a switch.

The main distinction between control computers and communications computers is that the task environment of the latter, since it consists of digitally encoded messages (even in the case of the voice telephone exchange), can be handled directly by the communications computer. That is, the communications computer can do the work of transshipment and storage as well as control.

Communications- and message-based computers have evolved from telephone switching control, message switching, and front ends to become dominant parts of communications systems. With these evolving systems, the communications links have changed from analog-based transmission to sampled-data digital transmission. With all-digital transmission, data, voice, and video can ultimately be used in the same system. Voice transducers enable speech communications with the computer.

The Electronic Switching System (ESS) processors of Bell Laboratories (Chap. 28) and BBN's Pluribus (Chap. 23) are two examples of communications computers.

Word processing (i.e., text creation, editing, and reproduction),


1The story above has been told exclusively in terms of IBM machines. Although this does not distort the picture too strongly in terms of total movements of the field, since IBM dominated the market, concurrent developments were taking place throughout the field. UNIVAC I was the first computer built by a manufacturer and did not have the idiosyncrasies we ascribe to IBM; on the other hand, the marketing effort for it was less.

2Apparently introduced in the UNIVAC 1103.

previous | contents | next