I sometimes think about the way that I learned about computers. I started out with a subscription to Popular Electronics magazine. At the time, I didn’t know much about electronics. I quickly learned about Ohm’s law which describes the behavior of electrical current in a resistive circuit. I picked up various details about other types of circuits and components by reading articles about them.
My dad’s cousin, Jim Shrewsbury had written an introductory book on radio. I read it cover to cover. I decided that I wanted to get an amateur radio license so I bought a copy of the ARRL Radio Handbook. I had trouble mastering morse code so I didn’t obtain a license until I was an adult. But I learned a lot about electronics.
In January 1975, Popular Electronics published the first installment of a two part article on building a small computer. Up until then, computers were large machines that took up lots of space and required lots of power. The idea of an individual owning one was rather novel. My imagination was sparked. I wanted one.
I read everything I could find about computers. I got access to a multi-user computer called Plato at the college library. When I was desperate for a job I enlisted in the Army for training in digital computer repair. After a struggle to pass basic training, I found myself in Huntsville, Alabama at Redstone Arsenal to learn how to fix the computers in the Pershing missile system.
The first part of the course taught us about digital logic, the basic building blocks of computers. Next, we learned about a small computer built specifically to teach how computers worked called the ComTran-10. I later learned that it was patterned closely after the Digital Equipment Corporation PDP-8 minicomputer. This was my first experience with writing assembly language programs for a computer.
Assembly language is the native language of a computer. It varies between computer models. Each assembly language instruction corresponds to an instruction that the central processing unit (CPU) of the computer executes natively. Once you’ve learned how to write programs in assembly language there is no program, in theory, that you can’t write.
That is of course a bold statement. It assumes that you can break down the problem into simple enough pieces that it can be expressed in assembly language. It also assumes that when you finish breaking down the problem, you have enough hardware resources, memory, CPU time, etc., to actually execute the program.
The way most modern programs are written are in higher level languages. Higher level languages are programs that translate programs from languages that are easier for humans to understand into the raw binary numbers that represent the assembly language instructions that the CPU can directly execute.
The process of translation is magical. The first higher level languages were written in assembly language. But then, the subsequent higher level languages could be written in the earlier higher level languages. In modern times, the only people that actually know assembly language are the people that design CPUs and the people that write higher level languages. (Even though the higher level languages are written in other higher level languages, the still have to generate assembly code as output.)
In the rest of the course, we studied the two computers that actually comprised the Pershing system, the guidance computer and the launch computer. We studied every component in the entire system. We learned to troubleshoot the system down to the individual component level. In the end, we knew how those computers worked.
When I got back to Redstone Arsenal from my tour in Germany, it was to spend the balance of my enlistment as an instructor in the school where I had learned about computers. By this time the Commodore Pet computer was being used to teach students about digital logic. The Pet was the forerunner of the famous Commodore 64 computer that many kids of a younger generation than me cut their computing teeth on. The Apple II and the Radio Shack TRS-80 were also on the market by then.
BASIC was the language that all of them were programmed in. It was the language that I used to become a journeyman programmer. It was exciting. It was more powerful than any language I’d programmed in before (with the possible exception of the Tutor language that the Plato system used). But for all that BASIC was an awful language. But it was the best thing that we had at that time.
That was a turning point in my career as a programmer and it will serve as a good stopping point in my story. In the next installment, I’ll give some examples of the kinds of programs that I wrote in BASIC and the languages that eventually replaced it.
Sweet dreams, don’t forget to tell the ones you love that you love them, and most important of all, be kind.