8 Bit Computers

Others from the United States

Apple II+ - 1979

I have only a single Apple computer in my collection but what a computer! The Apple 1 was designed in 1976 and made available as a kit. Since they did not come with a casing, you often see wonderful timber cases containing these early machines. In 1977, the Apple II was built, this came with a massive case. The reason was it had 8 slots for expansion cards just like a modern PC. You could add disk drive cards, high-res graphics etc and everything worked first time. The Apple itself had 4KB of RAM but expandable internally up to 48KB. It used the 6502 processor and an integer BASIC. The BASIC was coded manually and written on paper before being typed into ROM. It shows an amazing ability and patience. My own computer is a II+, this followed in 1979 and has 48KB of memory and a full BASIC (Applesoft). In the UK, it knocked spots off anything we had for some years though its horrendous price deterred all but the richest.

The Apple II probably sold far more to business use than it did to homes but those with the largest budgets did buy them hence their inclusion here.

In case any of you have been sleeping since 1979, the same company went on to build the Apple Mac, the iPod and the iPhone amongst many others. They are responsible for OSX, probably the finest operating system ever written.

A homage to Steve Wozniak

Having read Steve Woz's autobiography and having checked on the facts in his book , I decided to add to the Apple II description to honour his outstanding achievements. To put it into context it is necessary to back off one year (1975) to the first computer aimed at the home user, the MITS Altair. Out of the box (often as a bag of parts you put together yourself) it had 256 bytes of memory, display was a row of LEDs and it was programmed using switches, actually setting the relevant ones and zeros and adding each step in turn. The common configuration initially was to connect a teletype terminal. These were very expensive, heavy, noisy and very slow (tens of characters a minute). Output, being to paper, was in one direction only so limited to text output, line by line. There was usually a paper tape reader/writer attached which became a popular alternative to entering programs though the machien was still booted by a program entered on the switches.

Steve Woz was to change all that. He came from an engineering background with an aim of making the best solution with the lowest chip count (according to him, he later changed to lowest pin count after he was shown that a few massive chips with huge numbers of pins was not as good as a few more smaller chips with less pins). His invention, the Apple I, came from a number of previous inventions, the most notable being his Arpanet (precursor to the internet) terminal which could use any TV as a monitor. From his work in HP calculators division, he was also probably the first to hold software in ROM to instant start the computer. He developed using the MOS 6502 microprocessor and DRAM, both newly released. His original design used the 6800 processor as he was able to buy these much cheaper than the Intel 8080 used by everyone else. In search of the keenest price though he then moved to the 6502 as these were available at just $20 a piece and were pin compatible with the 6800 so no change in his design was required. He was also a very early adopter of Dynamic RAM (DRAM). As DRAM requires continual refresh (see note at footer), he designed his own hardware to do this, probably the first person to do so. That this could be added to his circuit board to replace the SRAM with very few changes is a reflection of his engineering genius. It also meant he could offer a computer with 8,000 bytes as standard and 48,000 maximum for a fraction of the price of the competition. The result was a microcomputer with a proper screen and keyboard, just like today.

His Apple II was virtually a masterpiece. On top of the first proper use of screen and keyboard came sound, game paddles and true hi-res graphics. He also wrote BASIC for the 6502 processor based on HP manuals and the whole thing coded by hand, mnemonics on the left and actual codes on the right of page after page, just over 4000 bytes of code. When you think he was never taught assembler then that is a very impressive result.

As someone who always thought himself an engineer then Steve Woz is definitely a hero. His original Apple I schematic he gave free to anyone who asked (and many even if they didn't) and only started building computers because his friends were unable to build their own. His Apple II was, in 1976, designed to permit anyone to have their own home microcomputer.

Note - RAM. Static RAM, comprises individual memory bits each using between 4 and 10 transistors. This makes the chip complexity high so difficult to place many bits on a single dual in-line chip. The original Apple I had just 2K of memory across 32 chips. The advantage of SRAM however is that it will retain values set in it as long as the chip has power.

Dynamic RAM, DRAM, uses tiny capacitors to store the data. A charged capacitor represents a 1 and a discharged one a zero. The problem is that capacitors discharge quite quickly by themselves so some external circuitry has to regularly (every 2 milliseconds in his case) rewrite the value of each bit to keep the 1s as 1s. The big advantage of DRAM is the size on the actual chip. One capacitor occupies a fraction of the space of 4 transistors. On the Apple 1, the SRAM version used 32 1K bit chips for 4K bytes (8 per K byte) compared with just 16 4K bit DRAMs providing 8K bytes.