The computers he is working with are 16 of the I.B.M, Series I minicomputers, which cost $10,000 to $25,000 and can perform a simple addition in 1.1 microseconds, or nearly a million additions a second. Fast, but the top I.B.M. computer—the 3033, which goes for $3.4 million—can add something in 58 nanoseconds, A nanosecond is a billionth of a second,

Mr. McMahon set about trying to explain what a program is.

Programs are commonly described as “a set of instructions.” Mr. McMahon agreed it was a sound definition, but he added:

“It must be remembered that the computer Is very unforgiving. If you tell a clerk to do something and your instructions are a shade off, the clerk will modify them and get the job done, 1 The computer does precisely what you tell it. Your instructions can be 99,9 percent correct, and the computer won't do what you intended. You're all right or all wrong.”

One pictures a programmer stooped over his computer terminal hour after hour, tensely tapping away. The truth is, applications programming is basically a paper and pencil business. A programmer doesn't see that much of a computer. Mr. McMahon figures he spends maybe a third of his time before a machine.

The first task of the applications programmer is to define the problem (which can take months) and lay out logical steps to its solution that the computer can follow (which can take months), Mr. McMahon works on his yellow pads—'I go through tons of them. I need a landfill for a wastepaper basket.” He puts something down, tears it up, tries a different approach. Computer lingo for the process is “iteration.” You try something, it bombs, you try again. You iterate. The better you are, the less you iterate.

Knotty problems like that posed by Holmes are just too mammoth for the mind to soak in all at once, so Mr. McMahon plans to split it into pieces, or “modules.” What's complicated about it is that computers are being asked to replace human judgment. Up until now, some 4,000 customers have had their alarms watched by men. Holmes wants computers to do the alarm watching and to decide how to act if and when an alarm goes off. But different customers require different procedures, which is evidenced by the fact that Holmes’ outline of the project fills a report the size of a phone book. All told, Mr. McMahon figures the program will involve more than 100,000 computer instructions. Whereas simple programs consist of five or six modules, this one is expected to run than thousand.

“When I get going on a project,” Mr. McMahon said, “I often let it float around at the back of my mind and don't bother it too much hoping a solution will form step by step. I sometimes see the program as a long train passing through my mina I know I'm together if I can follow each car as it chugs past, There's great glee, of course, when the caboose whips by.”

After a program design is done, Mr. McMahon starts to code it—to put it in computer language. Conciseness, is important; otherwise a lot of the computer's costly memory', where the data is stored, will be wasted. Mr. McMahon will write the Holmes program mostly in “assembly language,” hyphen in history. The rocket cost $18.5 million. but a fraction of it will be done in “FORTRAN,” which stands for formula translator. FORTRAN at least has a rough correspondence to English. Assembly language is a rampant mutation, made up of mnemonic symbols that stand for incredibly complex computer instructions. For example, “SFNED” stands for “scan byte field not equal and decrement,” and “FMVCD” sounds like a football play: “floating move and convert double.”