4004/6502/Z80/8008+ MicroprocessorsThe basis for any programmable computer (or even a calculator) is a microprocessor. Instead of covering each one in particular, we will cover the "similarities" between them and a little of their history. In doing so, you will gain a more firm grasp, and have the ability to either intelligently research them, repair their circuitry, or use them in a project you may be fabricating.
When computers were first starting out, they were nothing more than glorified calculators. As a matter of fact, the first true commercially manufactured "processor" chip was the 4004, which was manufactured by IBM for a Japanese calculator company, then a year later marketed as a computer processing "set". I say set, because the functions of a computer are so complex, that at the time they couldn't be done with just one single chip! It required a processor, a ROM, a RAM, and a shift register.
From IBM's standpoint, the growth of the processor began with the 4 bit 4004 processing chip, followed by the 8 bit 8008, then the 8080, the 16 bit 8086/8088, 80286, the 32 bit 80386, 80486, "Pentium"(586), 64 bit Itanium, etc. But what exactly is the bit about bits?
At this point, having some understanding of the basics behind computer languages is a little helpful. The programs you use (Open Office, Firefox, Angry Birds etc) are wonderful ways for you to use and interface with the computer - but in the end - the computer still only speaks 1's and 0's. A computer program may be written in "programming languages" like Java, C, or BASIC for that matter - but the computer STILL doesn't actually speak these languages. They have to either be interpreted, or compiled into 1's and 0's in order for the computer to understand what you want it to do. Computer Commands consist of a series of eight 1's and 0's, called a BYTE. Each individual digit (1 or 0) is called a BIT - short for Binary Digit. There are 8 BITs in one BYTE.
The IBM 4004 processor could only process 4 bits, or half a command, at a time. You would have to give it two 4 bit entries before it knew what to do. For instance, in order to write something into random access memory, you had to give the 4004 chip the command "1110 0000". Now memorizing all these one's and zeros in order is darn difficult. So we invented a computer language called ASSEMBLY language that eased the chore. Now they could say WRM which meant WRite to Memory. This three letter acronym was called a Mnemonic. Learning the Mnemonic Assembler commands allowed you to write directly to the processor. Later Interpreted languages and Compiled languages would create the Mnemonic program for you.
Of course, with the 4 bit computer, it would take 2 half-commands just to perform one command. If they could create an 8 bit computer, then the computer would be able to injest a whole command at a time, cutting the speed it would take to perform a task in half! In the hayday of computer growth - there were several competing "8 bit" processors that had a chance at conquering the world. The IBM 8000 series, The Motorola 6800 series, the 6502 (Apple II and Commodore), the Zilog (Tandy/Texas Instruments/Radio Shack) Z80.
So how is it that the IBM 8000 series won the processor wars? Well having seen it firsthand, and in my humble opinion, the overall effect was like this:
As stated before, the 4004 was only 1 of a family of chips that were required in order to build a computer. The complete list included:
The Z-80 was the foundation of the TRS-80 (Tandy-Radio Shack 80) computer. This computer sold for a bargain price of $2000, and that was a lot more money back in the late 70's than it is now. I can recall owning and using one of these. I now find it amazing that you can buy a fully usable laptop for $400 nowdays, and think you are paying too much!
The Zilog 80 (Z-80) chip, at best, was a cludge! Any engineer wanting to argue that can simply take a look at the pinouts of the chip compared to the pinouts of the 8008. They were randomly placed wherever it was convenient - not necessarily done with any plan or order. It was, however, a functional 8 bit processor and had a good command set. An adept programmer could make this computer do magic. It also had all the support that a multimillion dollar company could give it - unltil Tandy got wise to the fact it was inferior, and finally abandoned it.
Clearly the forerunner technologically in its day, the 6502 had built in color video (amazing at the time), and sound. Commodore Computers took advantage of this low priced chip and actively targeted the home computer user market. At only $600 for a whole usable computer (less than 1/2 the price of any of their competitors)- this naturally lent itself to a spawning generation of computer enthusiests, as they could not only balance their checkbook with it - they could play GAMES! If you haven't played it, you should try out ELITE- the first 3D first person shooter! Its graphics left a little to be desired by today's standards, but it certainly had a good plot, and would keep people glued to the computer for hours on end.
At this time Quanutm Link came about, and "linked" computers and people together across the entire American continent. It had access to university databases, chat rooms, News, online shopping - it was everything the internet would become, before the Internet knew it. At the time, the internet was a "secret" linking of university, government, and hospital computer systems. But then the internet joined forces with Q-Link, and something magical happened. The Internet BECAME what Q-Link was, and Q-Link changed its name... to America Online.
Note that Commodore wasn't the only computer to use the 6502 processor. It was just the best marketed and supported. The Apple II also used the 6502, and may have been the superior of the two computer designs, but it didn't sell nearly as many computers.
The 8008 was IBM's foray into the 8 bit scene. Having developed the 4004, the 8008 was simply an extension of technology for them. They were still wary of the "home computer" market, and didn't see it as really taking off. But when they saw the success of Commodore, they didn't want to be left behind - just in case. IBM created "The Personal Computer" the IBM PC
After the 8080, 8086, and 8088, they started working on 16 bit, 32 bit, and now even 64 bit computers, each doubling the possible processing speed of the computer. In the end, even the most complecated computer begins with the simplest of circuits - the transistor used as a NOT gate or inverted switch, and as such requires bias and ground to operate.
All microchips you ever run into will have the same testing procedures. Does it have Bias? Is the ground really grounded? Does it have a clock signal? Are all the inputs present? If all of the above is true, then it should have the correct outputs. If not, the chip is at fault. Most likely though, you'll find that the solution to your "chip related" problem has already presented itself by the time you asked the first three questions.
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