Apple II Accelerators

Apple II accelerators are computer hardware devices which enable an Apple II computer to operate faster than their intended clock rate.

Starting in 1977, most Apple II computers operated at a speed of 1 megahertz (MHz). That precedent was finally broken 10 years later in 1987 with the introduction of the Apple IIGS which ran at 2.8 MHz. Later, Apple Computer was able to release a 4 MHz Apple IIc Plus.

One of the difficulties with building faster computers were the limitations of the system bus on the motherboard. Many Apple II peripheral cards, such as the Disk II controller card which went into the computers' expansion slots were dependent on 1 MHz operation. Apple wanted to maintain hardware backwards compatibility throughout the product line and it was not economically feasible to engineer a work-around for this bottleneck. The other restriction was the limited availability of faster 65xx series of microprocessors which the Apple II family used. Western Design Center (WDC), the designer of the 65C02 (14 MHz) and 65C816 (14 MHz) microprocessors had difficulty procuring faster units, a cause of frustration and delays for both the original Apple IIGS and for the Apple IIc Plus. Some speculate that the lack of a wide availability of faster microprocessors from WDC is one of the reasons behind the demise of the Apple II.

In the early-mid 1980s, as the available list of Apple II application software grew and these applications became more processor intense, users wanted to have faster machines. Third-party hardware manufacturers came up with some innovative ways to bypass the 1 MHz limit. Initially, accelerator expansion cards recreated the combination of CPU and memory logic of the Apple II onto the card itself. These cards went even further by copying the Apple II ROM code into the card's fast RAM, essentially creating an Apple II on a card. Virtually all of these cards ran at a speed of 3.58 MHz, derived by dividing the 7 MHz signal on the expansion bus by a factor of 2. Incremental 1.7 MHz "half" speeds were available through further division. Later Apple II accelerators used separate on-board crystal oscillators to control speed timing and implemented complex caching techniques with small amounts of fast cache memory to do the acceleration. This type of design likewise allowed for easy upgradeability and was the primary method used in Apple IIGS accelerators.

The Apple II accelerator market was fiercely competitive and could be looked upon as somewhat of a soap opera. Microcomputer Technologies (M-c-T) was an early player with their cache based SpeedDemon card. The company later split up and some of the partners set up Zip Technologies who developed the Zip Chip, while other employees created a company called Bits and Pieces, manufacturers of the Rocket Chip. Zip Technologies successfully sued Bits and Pieces for patent infringement and consequently forced them out of business. As a result, Applied Engineering was forced to discontinue their new TransWarp II accelerator due to their licensing of technology from the Rocket Chip. After the dust settled, Zip Technologies remained the lone player in the 8-bit Apple II accelerator market with Apple Computer licensing Zip's caching technology for the Apple IIc Plus.