Which Computer ? -- Time-Sharing


By N. LEE BEYER [Applications Specialist Information Services Marketing Dept., General Electric Co.]

(source: Electronics World, Nov. 1971)

A time-sharing terminal puts "creativity" back into engineering by eliminating time-consuming, repetitive and complex calculations and permitting the simulation of complete designs.

HOW many times have you had a good design idea only to have it get bogged down in the myriad problems which crop up in attempting to bring it to fruition? Problems like:

Simple calculations which must be repeated over and over

Computations which are too complex for your slide-rule, pencil, or patience

Breadboarding and testing, which cuts into your parts inventory (what inventory ?) and requires the use of test equipment (someone dropped it?)

Despite these obstacles, suppose your idea begins to see daylight. Now you must consider design optimization. How sensitive is voltage to component variation? What should the tolerances be? What alternatives should be considered? Can the deadline be met?

Successfully overcoming these problems, which are encountered almost every day in design work, is critical to "creative" engineering. But too often the desire for creativity gives way to expediency or even abandonment of the idea. This is where computer time-sharing comes in. It can give you the time to be creative by quickly performing those repetitive and often complex calculations. Or you can have it simulate complete designs and perform "knob twisting" and analysis of alternatives. Time-sharing is the easy-to-use tool which will allow you to do all these things and many more.

Time-Sharing is Personal Computing

To many people, the thought of using a computer is actually frightening. Many regard it as a super-genius that is the ultimate in automation and does away with the need for a human brain, hands, ingenuity, and the privilege of making a decision.

Time-sharing, often referred to as "personal" computing, is quite different. And, unlike having a computer, you don't need to be a large company or operation to afford timesharing. In fact, many one -man consulting and design firms have the service in their offices or homes.

Time-sharing service enables you to use a multi-million-dollar computer system for your own calculations and analysis on much the same basis as you use the telephone. You get all the benefits of the remote system and related equipment, but pay only for the time you're "talking" to the computer over regular telephone lines from a typewriter like terminal by your desk.

The distant computer system is usually accessible by dialing a local telephone number from the terminal. Once connected with the computer, it is nearly as easy as a typewriter or telephone to use.

While you are working with the computer, so are dozens of other people. Of course, you have to talk in a language which both you and the computer understand. So, "conversational" languages have been developed using ordinary English words and phrases. The whole thing seems pretty ordinary, until you have the experience of using it.

Time-sharing makes the computer a personal tool that is available and responsive when you want it. For design engineers and technicians, timesharing service becomes an inexpensive and extremely efficient laboratory in which to experiment with ideas. For example, "what if' questions can be answered quickly and then different approaches investigated while the previous steps are still fresh in your mind.

Time-sharing, then, is a new capability that makes it possible for engineers, technicians, scientists, businessmen, students, and even housewives, to obtain the benefits of modern computer systems. Charges are based on the actual time used. It is easy to learn and use, thanks to the simplified languages. It is extremely resourceful. And with a little experience, most users can develop their own applications programs while also having full access to the extensive program libraries available from most commercial time-sharing service firms.

Time-Sharing in Engineering

Engineers were pioneers in the use of time-sharing, which was first offered on a commercial basis in 1965 by General Electric Company. Time-sharing is now applied in all fields of engineering and has become an indispensable tool in many design projects.

Structural engineers in electric utilities use time-sharing to help design and analyze transmission towers. Design alternatives and customized structures can be evaluated in a fraction of the time previously required using other means. Mechanical engineers use time-sharing to study the performance of vehicle suspension systems.

Power-systems engineers use timesharing to determine the effect of three-phase and line-to-ground faults at various points within an electrical distribution system. The economic evaluation of all alternatives enables them to place the necessary equipment in the best location so as to minimize the effects of these faults should they occur.

In the field of electronics, time-sharing has played a significant role for many years. It has been used to analyze very simple circuits; to design filters and transformers; to simulate the performance of entire networks; and to optimize component layout and generate necessary artwork.

Typical Electronics Applications

The classic example of time-sharing use in electronics is circuit analysis. Programs such as ECAP (Electronic Circuit Analysis Program) have received much attention and have been used by circuit designers for many years.

This particular program allows you to breadboard your circuit on the computer by describing circuit topology and component values in simple, easy-to-understand terms.

ECAP will then perform the desired analyses of the circuit.

For example, suppose you want to determine the frequency response of the single -stage amplifier shown in Fig. 1A using time-sharing and the ECAP program.

First you would dial the computer over regular telephone lines from your office typewriter-like terminal. You would then describe to the computer your circuit topology, component values, and the analyses you want to perform.

This procedure would take a few minutes. Fig.1B shows a listing of the information that describes this single-stage amplifier.

In line 1040 of the description you have requested an a.c. analysis. In line 1170, the load resistor is shown to have a value of 100k and is in branch 12 (B12) which lies between nodes 5 and ground [N (5, 0)]. In line 1230 a scaled plot of the voltage and phase at node 5 is requested.

Fig. 1C shows the resulting analysis produced by the ECAP program. From these results, you could easily make circuit modifications and rerun the analyses in a matter of minutes. In this way, you can evaluate alternatives and optimize your design, without the necessity of finding parts, checking out equipment, or waiting days or weeks for results.

Fig. 1 (A) Single-stage amplifier to be analyzed for frequency response. (B) Complete listing of information describing circuit, (C) Resulting analysis produced by ECAP.

Fig. 2. Result produced by circuit-analysis program indicating how sensitive a node voltage is to 1% component value change.

One distinct advantage of using computer time-sharing programs for circuit design and analysis is the statistical information which these programs can provide about your circuit's behavior. Such data would be too time -consuming and laborious to obtain manually.

Fig. 2 is the result produced by a circuit-analysis program indicating how sensitive a node voltage is to a one-percent change in the value of various components. Often referred to as a sensitivity analysis, it shows which components have the most effect on circuit performance and thus you can, for example, adjust the tolerances accordingly.

Fig. 3. (A) Checking out performance of 4-bit ripple through counter. (B) Description of counter's components and layout using GE's "Logic" program. (C) Timing diagram output.

Fig. 4. Part of the results of "conversing" with "Array" terminal.

Digital Systems

Another major use of time-sharing in electronics is in the design of digital systems. As a simple example, suppose you need to check out the performance of the 4-bit ripple through the counter shown in Fig. 3A. One of the many time-sharing programs available for simulating digital systems could be used.

Using GE'S "Logic" program, you would first describe the counter's components and layout. Fig. 3B shows the information contained in such a description. Fig. 3C is the timing diagram that would be produced at your office terminal. Should such results not be satisfactory, you can quickly make modifications and produce additional results in minutes. Although only a few modules were used in this example, the program can handle a network containing up to 500 modules consisting of logic gates, flipflops, counters, registers, etc.

Antenna Design

Characteristic of timesharing service is the "conversational" manner in which it operates. This means that both you and the computer "talk" to solve your problem.

For example, suppose that you are designing a special linear antenna array and you want to plot the antenna pattern. Fig. 4 shows part of the results of conversing with a program called "Array" from your terminal. The program requested the number of elements in the array (N), the polar angle increment for the plot (delta), the number of wavelengths separating each element in the array (D), and the progressive phase shift between elements in the array (alpha). You would supply the answers as italicized to obtain the resulting plot.

The two-way English language conversation carried on between you and the computer makes timesharing extremely easy to learn and use. And, if you make mistakes, the computer will usually notify you immediately so that you can take the appropriate corrective action.

System Dynamics

Most design projects at some point involve a study and analysis of the design's dynamic behavior. A common solution to the problem has been the use of analog computers, which allows you to model and analyze the system dynamics. However, there are many time-sharing programs which simulate the operation of analog computers and enable you to study dynamic performance.

For example, suppose you wanted to determine the controlled response of the feedback system in Fig. 5A. Fig. 5B shows a typical analog block diagram describing this particular system. If an analog computer were used to provide a solution, you would have to wire up a patch-board describing this block diagram. Using the time-sharing program "Dysim," you would merely describe the block diagram to the computer.

Fig. 5C is a plot of the controlled response produced at the terminal in response to the command "Plot 3." The entire process took a few minutes and you could easily perform on-line modifications to your block diagram if the response were not satisfactory.

These examples can only begin to demonstrate the versatility of time-sharing and its significance in the field of engineering. But they illustrate why many engineers, designers, and technicians have found time-sharing an indispensable tool in obtaining creative solutions to both the simple and complex problems which they face. Even companies with extensive in-house data-processing systems subscribe to timesharing because it is accessible to the man with the problem when he needs a solution. And most users gain considerable value from on-line libraries of application programs, such as those described here, which help them obtain immediate and effective use of time-sharing without having to become a computer programmer.

The exciting thing about this "personal computer" service is that its use and potential is limited only by the person using it. But to fully evaluate how time-sharing can help put more creativity into your engineering activities, arrange for a personal visit by one or more of the 100 or so firms now marketing commercial service throughout the country. In your initial meeting, be prepared to review your engineering tasks and problem-solving requirements.

From this first meeting, the timesharing representative can put together a special proposal of services, capabilities, and programs tailored to your needs. To be presented at a second meeting, this proposal should cover:

1. A description of specific services and programs available.

2. What initial and follow -up training does vendor provide and at what cost?

3. What personnel support does the supplier provide to assure your effective use of the service?

4. A clear definition of monthly charged.

5. Examples of documentation describing the various services and programs.

6. Types of contractual agreements, if any, that you must sign.

7. A full demonstration of appropriate programs and capabilities.

After reviewing the various proposals, it should be clear which supplier can best provide the service you require.

Before you know it, you'll be on your way to creative problem-solving with your own personal timesharing computer. Within a short time, you'll be writing your own special application programs.

Fig. 5. A time-sharing terminal is a compact, desk -top unit which lets engineer "tap " the memory of a full size computer.

Fig. 5. (A) Feedback system on which controlled response is to be determined. (B) Typical analog block diagram describing the system. (C) Plot or response produced by "Dysim."

Top of Page

PREV: (none) NEXT |  Guide Index | HOME