Inside the Apple III
By Gabriel Torres on May 31, 2012
The Apple III (or, more correctly, Apple ///), codenamed “Sara,” was released in 1980 to be a “business” microcomputer. In this tutorial, we will take an in-depth look at its hardware and understand why it was Apple’s first failure.
There were three revisions of the Apple III. The first one presented an infamous stability problem, where the computer would crash for no apparent reason. Initially, it was thought that this was caused by overheating, as the Apple III didn’t have any fan and there was not enough space for air to circulate inside the machine. (The first computers from Apple didn’t have a fan because Steve Jobs thought fans were not elegant and produced noise; he wanted computers to be as quiet as possible. Fans were only added to Apple computers after he left the company.) The heat problem caused integrated circuits to pop from their sockets. It also created poor contact between the motherboard and the memory board, which didn’t use golden connectors as it should have. Another problem with the original Apple III was that its clock/calendar circuit simply didn’t work. This led to the infamous technical note where Apple recommended users facing problems with the Apple III to lift the computer two inches and drop it, as this would set the circuits back in place. This problem gave the Apple III a bad name and hurt sales, but it wasn’t the only reason why this computer wasn’t successful. (We will explore all of the reasons later.)
A revised version of the Apple III was released in early 1982, replacing all of the sockets and removing the clock/calendar circuit, which was now optional. Owners of the first revision could also replace their computers with the revised version for free. Whereas the original Apple III had 128 kB of RAM (+12 V chips), the revised version had 256 kB (+5 V chips). This is the model we are using in this tutorial.
Later, it was discovered that the problem was, in fact, with the motherboard manufacturing process, which was creating contacts were there shouldn’t have been any. A third version of the Apple III, called the Apple III Plus, was released with a new motherboard, which incorporated the clock/calendar circuit again. Its keyboard was yellow (the same color as the keyboard of the Apple IIe) instead of brown as on the previous versions. It was short-lived, as it was released in December 1983, and the entire Apple III line was officially discontinued in April 1984.
In Figure 1, you can see a “complete” Apple III system, with the computer at the bottom, its optional 5 MB external hard drive (“Profile”) in the middle, and its video monitor (“Monitor III”) at the top. The video output of the Apple III used the composite video format, so any composite video monitor would work with it; the Monitor III also worked with any device with composite video.
In Figure 2, you can see the Apple III by itself.
The Apple III had a built-in 5.25”, 143 kB floppy disk drive. It ran an exclusive operating system called Apple SOS, which stands for Sophisticated Operating System. Apple wanted people to pronounce “SOS” as “sauce” (“apple sauce”), but the joke of calling it S-O-S after its big flop was unavoidable.
The Apple III used a mechanical keyboard that was visibly different from the one used on the Apple II and Apple II Plus. It had a numerical keypad, allowed the use of both upper case and lower case letters, thus the presence of the “Alpha Lock” (“caps lock”) key (the Apple II and Apple II Plus by default only allowed upper case letters), the presence of the new Open Apple and Solid Apple keys, and the reset key was now hidden behind the keyboard.
On its rear side, the Apple III had a connector for an external floppy disk drive, two I/O ports (mainly targeted to joysticks), an RGB video output, a composite video output, an audio output (for connecting to external speakers; the computer had an internal speaker as well), a serial port, a receptacle for the power cord, and the on/off switch. The first I/O port supported the direct installation of an Apple Silentype printer, which was a thermal printer. As you can see, the Apple III had four expansion slots. In Figure 4, you will notice that we had an expansion card installed; this was the Profile interface card for the Profile external hard drive.
In order to remove the Apple III’s top lid to have access to its interior (for installing expansion cards, for example), you needed to remove two screws located at the bottom of the computer. In Figure 5 you can see the Apple III with its top lid removed.
As mentioned, there were four expansion slots, and our Apple III had a Profile interface card installed, which must have been installed in slot four. Other expansion cards available at the time included a CP/M card (which had a Z80 microprocessor that allowed the Apple III to run the CP/M operating system and programs written for this OS), memory expansion, and an Apple IIe emulator. But the truth is, few hardware manufacturers got interested in developing peripherals for the Apple III.
Let’s now take an in-depth trip inside the Apple III.
The Apple III was based on the 6502 microprocessor, the same one used by the Apple II and Apple II Plus computers (the Apple IIe and the Apple IIc used the 65C02 processor). This microprocessor was also used by some other microcomputers at that time, such as the Commodore 64, the Commodore VIC-20, the Atari 400, and the Atari 800, just to name the most famous ones. The 6502 was a stripped-down version of the Motorola 6800 processor. The 6502 was originally designed by MOS Technology, but it was also licensed and manufactured by other companies. In the case of the Apple III, the 6502 vendor was Synertek.
The Apple II used the “original” 6502 running at 1 MHz; however, on the Apple III the processor worked at 2 MHz, so from a pure processing standpoint, the Apple III was twice as fast as the Apple II. The original Apple III used the 6502A processor, which was rated at 2 MHz. The revised Apple III and the Apple III Plus used the 6502B processor, which could handle up to 3 MHz, but its clock rate was fixed at 2 MHz, so using a “faster” CPU in this case was nonsense. With microprocessors from the 1970s and early 1980s, a letter after the “name” of the processor indicated the maximum supported clock rate (that doesn’t mean that the CPU would work at that rate).
The 6502 could only access up to 64 kB of memory (RAM and ROM), but through a technique called bank switching, the Apple III could access up to 512 kB of RAM, although it came with 128 kB (original version) or 256 kB (revised version and the Apple III Plus). The memory chips were located on a daughterboard installed on the motherboard. On the 256 kB version, 32 chips of 64 Kbits were used (64 Kbits x 32 = 256 kB).
Similarly to the Apple II and Apple II Plus, the Apple III used mostly “regular” TTL integrated circuits that you could buy at any electronic components store. The biggest integrated circuits, besides the 6502 microprocessor, were two 6522 “Versatile Interface Adapters” for I/O communications and one custom keyboard controller called 341-0035. The empty socket located on position “B3” of the motherboard was reserved for the 58167 clock/calendar integrated circuit, which was now optional, as previously mentioned. Other “big” chips used on the Apple III motherboard included the 6551 serial controller, a custom video mode selector called 341-0032 (which was actually a ROM chip), and a custom video elements/attributes generator called 341-0030 or 2316.
The Profile external 5 MB hard drive was released in September 1981 as an optional peripheral for the Apple III, at a cost of USD 3,500. In 1983, Apple released a Profile interface card for the Apple II computer line, allowing Apple II computers to use the Profile as well (except for the Apple IIc, since it was a portable computer without an expansion slot). The Profile was also compatible with the Apple Lisa, without the need for an additional interface card. This hard drive was not compatible with other computers.
In Figure 13, you can see the interface card for connecting the Profile to the Apple III. They were connected using a 25-pin cable. This interface should have been installed in Apple III’s fourth slot.
Internally, the Profile used a Seagate ST-506 hard disk drive, but an interface designed by Apple. You couldn’t upgrade the internal hard drive directly. (This upgrade was possible, but you needed to upgrade an integrated circuit on the logic board.)
Believe it or not, there are still people developing hardware for old computers. Currently, you can buy an X/Profile, which is a Profile emulator based on the Compact Flash (CF) card. It allows you to use a Compact Flash (CF) card as a hard drive for your Apple III. In other words, create an SSD (Solid State Drive) for your vintage Apple III.
The Apple III was a huge failure for several reasons. The most obvious one was that its implementation was flawed, as the computer crashed for no apparent reason. The revised model still faced problems as Apple fixed the sockets on the motherboard, but the motherboard manufacturing process ended up being the real culprit. The Apple III was only fixed with the Apple III Plus, but by the time it was released, it had already become infamous for being a faulty computer. (And, by that time, IBM had already released its second microcomputer and main competitor to the Apple III, the PC XT, which cost less.) The Apple III Plus had a shelf life of only four months, as Apple decided to simply kill the Apple III.
The second major problem was that it was very expensive. The revised Apple III cost USD 3,500, plus the price of the monitor. If you wanted a hard drive, you would have to pay an extra USD 3,500 for getting the Profile 5 MB external drive. So, a complete Apple III system in 1982 would cost more than USD 7,000 (USD 16,700 in 2012 dollars).
The third problem is that it was not 100% compatible with the Apple II. The Apple III could run in Apple II compatibility mode, but it would emulate a basic Apple II without any add-on cards. This meant that Apple II programs would run in 40-column display instead of 80-column, even though the Apple III supported 80-column display, and the programs wouldn’t access all of the available memory. So, there were no incentives for companies to upgrade from their working Apple II systems with 80-column cards and memory expansion cards to the Apple III. In fact, you could buy a complete Apple II system for far less, and you would have many more programs available.
By the end of 1983, Apple had sold only 75,000 units of the Apple III, while it was selling around this number of Apple IIe units per month. (Apple sold 1.3 million units of the Apple II and its variants by the end of 1983.)
According to Steve Wozniak, the problem with the Apple III was that it was designed by committee, meaning that the project didn’t have a leading engineer who decided how the Apple III would be constructed. What happened was that everybody at Apple gave their opinion about how the Apple III should be built, and when everything was put together, it was a disaster. Or, as Randy Wiggiton, one of the engineers, put it: “The Apple III was kind of like a baby conceived during a group orgy, and later everybody had this bad headache, and there’s this bastard child and everyone says, ‘It’s not mine.’”