This looks set to be my final post of this series about the history and functional mechanics of computers. Today I want to get onto the nuts & bolts of computer programming and interaction, the sort of thing you might learn as a budding amateur wanting to figure out how to mess around with these things, and who’s interested in exactly how they work (bear in mind that I am not one of these people and am, therefore, likely to get quite a bit of this wrong). So, to summarise what I’ve said in the last two posts (and to fill in a couple of gaps): silicon chips are massive piles of tiny electronic switches, memory is stored in tiny circuits that are either off or on, this pattern of off and on can be used to represent information in memory, memory stores data and instructions for the CPU, the CPU has no actual ability to do anything but automatically delegates through the structure of its transistors to the areas that do, the arithmetic logic unit is a dumb counting machine used to do all the grunt work and is also responsible, through the CPU, for telling the screen how to make the appropriate pretty pictures.
OK? Good, we can get on then.
Programming languages are a way of translating the medium of computer information and instruction (binary data) into our medium of the same: words and language. Obviously, computers do not understand that the buttons we press on our screen have symbols on them, that these symbols mean something to us and that they are so built to produce the same symbols on the monitor when we press them, but we humans do and that makes computers actually usable for 99.99% of the world population. When a programmer brings up an appropriate program and starts typing instructions into it, at the time of typing their words mean absolutely nothing. The key thing is what happens when their data is committed to memory, for here the program concerned kicks in.
The key feature that defines a programming language is not the language itself, but the interface that converts words to instructions. Built into the workings of each is a list of ‘words’ in binary, each word having a corresponding, but entirely different, string of data associated with it that represents the appropriate set of ‘ons and offs’ that will get a computer to perform the correct task. This works in one of two ways: an ‘interpreter’ is an inbuilt system whereby the programming is stored just as words and is then converted to ‘machine code’ by the interpreter as it is accessed from memory, but the most common form is to use a compiler. This basically means that once you have finished writing your program, you hit a button to tell the computer to ‘compile’ your written code into an executable program in data form. This allows you to delete the written file afterwards, makes programs run faster, and gives programmers an excuse to bum around all the time (I refer you here)
That is, basically how computer programs work- but there is one last, key feature, in the workings of a modern computer, one that has divided both nerds and laymen alike across the years and decades and to this day provokes furious debate: the operating system.
An OS, something like Windows (Microsoft), OS X (Apple) or Linux (nerds), is basically the software that enables the CPU to do its job of managing processes and applications. Think of it this way: whilst the CPU might put two inputs through a logic gate and send an output to a program, it is the operating system that will set it up to determine exactly which gate to put it through and exactly how that program will execute. Operating systems are written onto the hard drive, and can, theoretically, be written using nothing more than a magnetized needle, a lot of time and a plethora of expertise to flip the magnetically charged ‘bits’ on the hard disk. They consist of many different parts, but the key feature of all of them is the kernel, the part that manages the memory, optimises the CPU performance and translates programs from memory to screen. The precise translation and method by which this latter function happens differs from OS to OS, hence why a program written for Windows won’t work on a Mac, and why Android (Linux-powered) smartphones couldn’t run iPhone (iOS) apps even if they could access the store. It is also the cause of all the debate between advocates of different operating systems, since different translation methods prioritise/are better at dealing with different things, work with varying degrees of efficiency and are more or less vulnerable to virus attack. However, perhaps the most vital things that modern OS’s do on our home computers is the stuff that, at first glance seems secondary- moving stuff around and scheduling. A CPU cannot process more than one task at once, meaning that it should not be theoretically possible for a computer to multi-task; the sheer concept of playing minesweeper whilst waiting for the rest of the computer to boot up and sort itself out would be just too outlandish for words. However, a clever piece of software called a scheduler in each OS which switches from process to process very rapidly (remember computers run so fast that they can count to a billion, one by one, in under a second) to give the impression of it all happening simultaneously. Similarly, a kernel will allocate areas of empty memory for a given program to store its temporary information and run on, but may also shift some rarely-accessed memory from RAM (where it is accessible) to hard disk (where it isn’t) to free up more space (this is how computers with very little free memory space run programs, and the time taken to do this for large amounts of data is why they run so slowly) and must cope when a program needs to access data from another part of the computer that has not been specifically allocated a part of that program.
If I knew what I was talking about, I could witter on all day about the functioning of operating systems and the vast array of headache-causing practicalities and features that any OS programmer must consider, but I don’t and as such won’t. Instead, I will simply sit back, pat myself on the back for having actually got around to researching and (after a fashion) understanding all this, and marvel at what strange, confusing, brilliant inventions computers are.