The Beginner's Page
COMPUTE! is a specialized resource magazine that provides editorial coverage of a family of microcomputers that share a common "central processing" chip — the 6502. With the proliferation of small computers, we find that you can obtain more useful and relevant information in a magazine that doesn't (for example) cover the TRS-80 computer line. It, by the way, uses a different microprocessor chip: the Z-80. A whole different family of chips, and a different family of machines.
We're organized sequentially, with the front section of the magazine devoted to material of general interest and utility. The following sections are devoted to specific machines. These are called Gazettes, and contain information pertinent to your special machine. Frequently, however, you'll find useful material in other sections (Gazettes) of the magazine.
Where The Sets Merge, Or Common Interests
All of your machines have available a programming language called BASIC. BASIC stands for Beginners All-purpose Symbolic Instruction Code. It's what is called a higher-level language. BASIC differs somewhat on the different machines, so you'll find some things in common with other BASIC's and some differences. In practice, BASIC simply makes it easier for you to talk to your 6502 microprocessor. The 6502 sits at the heart of your machine. It and supporting "firmware" and "hardware" make your machine capable of doing what it does. In a nutshell, you feed your 6502 instructions that it can act on. It only acts on very picky little sets of numbers, and that's why you have BASIC. BASIC serves as an English-language like translator for you, taking your instructions in a pseudo-English format and translating them for the 6502.
Other portions of firmware contribute to your machine's features. Someone has already written a 6502 program that resides in your machine, interacting with BASIC, and passing out instructions to the 6502. This program (or set of programs) is called the Operating System. It is permanently inscribed onto a chip or set of chips inside your machine. Its permanence implies its generic name: firmware. Hardware characteristics also help define your machine and its capabilities. Memory is one important characteristic. Memory is your working space. It's much like the work area you have on top of your table. Let's assume you have a table of x size, and you're ready to start a project. You have a set of notes and instructions previously developed to help you with your task. Let's also assume that you may not write on your previous notes, but you may refer to and use them freely. These notes and instructions are much like one kind of memory in your computer: ROM. Read Only Memory is memory that has a program already saved on it. The program doesn't go away when you turn your machine on and off. This, then, is your firmware: the ROM, or set of ROMs, where "permanent" programs, or sets of instructions, reside. The number of instructions your Operating System can have, e.g. in part its complexity, is then directly related to the amount of ROM in your machine. Let's stack up these beginning "notes" on one side of your desktop. We'll assume that they take up one-quarter of the table space. We can use them always, but we can't stack anything else there.
Now let's add a clean notepad to our workspace. We'll call this our work area. Everytime we come back to our desk to work, we'll assume we have x amount of clean space to put our notepad on, and do whatever work we want. This "flexible" work area equates to RAM. Random Access Memory is another type of memory inside your computer. Unlike ROM, which has a set of instructions "built-in", RAM is empty. It's your working area; the space you use for putting in your own information. After you put something in it, you can use it, reading from it later, and so on, just like your note pad. And like your notepad, you can continue to return to it, reading from it and writing to it. Until, of course, you turn your computer off. Your RAM is wiped clean when the power goes away.
This is why your computer has a storage device. Whether it's a tape cassette or a disk drive, it's there to save the contents of your RAM. Let's assume you've entered a set of instructions. We know where they are: they're in RAM. We also know that once the machine is turned off, these instructions will be erased from RAM. The solution is simple. Save them somewhere. When you want them back, your Operating System will take care of reading them back into RAM.
Where Are We?
We've just covered the areas that make your small computer a truly remarkable and powerful device. It has a set of predefined features, controlled by permanent instructions, and aided by design features that always make it "act" the same way. Your calculator is much like this; and your microwave oven; and the host of other consumer products that are utilizing some form of microprocessor chip. The firmware in these devices is simply a set of permanent instructions to a computer chip. But your computer has a whole lot more. It has RAM, allowing you work space to develop your own sets of instructions to your computer chip. Aha! Tremendous flexibility. And it has a storage device, allowing you to save the effort of your labors, retrieving them at will for use and further development.