Chapter 3: Lifting the Hood Discovering What Computers Actually Are

RAXie, We Hardly Knew Ye...

In January 1970 I was on the downwind leg of my senior year in high school, and the Chicago Public Schools had installed a computer somewhere. A truckful of these fancy typewriter gimcracks was delivered to Lane Tech, and a bewildered math teacher was drafted into teaching computer science (they had the nerve to call it) to a high school full of rowdy males.

I figured it out fairly quickly. You pounded out a deck of these goofy computer cards on the card punch machine, dropped them into the hopper of one of the typewriter gimcracks, and watched in awe as the typewriter danced its little golfball over the greenbar paper, printing out your inevitable list of error messages. It was fun. I got straight A's. I even kept the first program I ever wrote that did something useful: a little deck of cards that generated a table of parabolic correction factors for hand-figuring telescope mirrors, astronomy being my passion at the time. (The card deck is still in its place of honor on the narrow shelf here in my second-floor office, next to my 8-inch reel-to-reel tape deck and my father's venerable slide rule.)

The question that kept gnawing at me was exactly what sort of beast RAX (the computer's wonderfully appropriate name) actually was. What we had were ram-charged typewriters that RAX controlled over phone lines-that much I understood. But what was RAX itself?

I asked the instructor. In brief, the conversation went something like this:

ME: "Umm, sir, what exactly is RAX?"

HE: "Eh? Um, a computer. An electronic computer."

ME: "That's what it says on the course notes. But I want to know what RAX is made of and how it works."

HE: "Well, I'm sure RAX is all solid-state."

ME: "You mean, there's no levers and gears inside."

HE: "Oh, there may be a few. But no vacuum tubes."

ME: "I wasn't worried about tubes. I suppose it has a calculator in it somewhere. But what makes it remember that A comes before B? How does it know what FORMAT means? How does it tell time? What does it have to do to answer the phone?"

HE: "Now, come on, that's why computers are so great! They put it all together so that we don't have to worry about that sort of thing! Who cares what RAX is? RAX knows FORTRAN and will execute any correct FORTRAN program. That's what matters, isn't it?"

He was starting to sweat. So was I. End of conversation.

That June I graduated with three inches of debugged and working FORTRAN punch cards in my bookbag, and still had absolutely no clue as to what RAX was.

It has bothered me to this day.

Gus to the Rescue

I was thinking about RAX six years later, while on the Devon Avenue bus heading for work, with the latest copy of Popular Electronics in my lap. The lead story involved a little thing called the COSMAC ELF, which consisted of a piece of perfboard full of integrated circuit chips, all wired together, plus some toggle switches and a pair of LED numeric displays.

It was a computer. (Said so right on the label, heh.) The article told us how to put it together, and that was about all. What did those chips do? What did the whole thing do? It was driving me nuts.

As usual, my friend Gus Flassig got on the bus at Ashland Avenue and sat down beside me. I asked him what the damned thing did. He was the first human being to make the concept hang together for me:

"These are memory chips. You load numbers into the memory chips by flipping these switches in different code patterns. Each number means something to the CPU chip. One number makes it add; another number makes it subtract; another makes it write different numbers into memory, and lots of other things. A program consists of a bunch of these instruction-numbers in a row in memory. The computer reads the first number, does what the number tells it to do, and then reads the second one, does what that number says to do, and so on until it runs out of numbers."

If you don't find that utterly clear; don't worry. I had had the advantage of being an electronics hobbyist (so I knew what some of the chips did) and had already written some programs in RAX's FORTRAN. But for me, my God, everything suddenly hit critical mass and exploded in my head until the steam started pouring out of my ears.

No matter what RAX was, I knew that it had to be something like the COSMAC ELF on a larger scale. I built an ELF. It was quite an education, and allowed me to understand the nature of computers at a very deep level. I don't recommend that anybody but total crazies wirewrap their own machines out of loose chips anymore, although it was a common enough thing to do in the mid-late seventies.

As a sidenote, someone has written a Windows-based simulation of the COSMAC ELF that looks just like the one I built, and will actually accept and execute COSMAC programs. It's a lot of fun and might give you some perspective on what passed for computing in early 1976. The URL is as follows:

www.incolor.inetnebr.com/bill_r/computer_simulators

The site's author, Bill Richman, has also reprinted the Popular Electronics article that I built the device from. All fascinating reading-and a very good education in the deepest silicon concepts underlying computing as it was then and remains to this day.

In this chapter I try and provide you with some of the insights that I obtained while assembling my own machine the hard way. (You wonder where the "hard" in "hardware" comes from? Not from the sound it makes when you bang it on the table, promise...)