Ferguson Big Board

The Big Board (1980) and Big Board II (1982) were Z80 based single-board computers designed by Jim Ferguson. They provided a complete CP/M compatible computer system on a single printed circuit board, including CPU, memory, disk drive interface, keyboard and video monitor interface. The printed circuit board was sized so as to allow attachment to an 8 inch floppy disk drive. The Big Board II added a hard disk drive interface, enhancements to system speed (4 MHz vs. 2.5 MHz) and enhancements to the terminal interface.

One version of the Big Board was used in the Xerox 820.

The Big Board was sold as an unpopulated printed circuit board with sockets for integrated circuits, with documentation and options to purchase additional components . The Big Board design was simple enough to build a system around that many people with no prior electronics experience were able to build and bring up a capable computer system of their own at a cost far less than that of a fully assembled system of the time. In this way, the Big Boards anticipated the DIY PC clones that became popular later. In its most popular form, the fully assembled and tested Big Board need only be connected to a power supply, one or two eight inch floppy disk drives, a composite monitor, and an ASCII encoded keyboard in order to provide a fully functioning system. A serial terminal could be used in place of the monitor and keyboard, further simplifying assembly. The only tool required for basic assembly was a screwdriver for the terminal block power connections.

The design was also simple to modify for the sake of system expansion and enhancement. Many different modifications to increase the system clock speed were possible, including some that required nothing more than jumpers (e.g. the 3.5 MHz speed upgrade obtained by jumpering the clock divider, with no software modifications or changes to the ICs on the board.) There was also a minor industry in user-installable system upgrades such as real time clocks, 4 MHz upgrades, double density floppy upgrades, character enhancements for the display (reverse video, blinking, etc.), and the addition of hard disk interfaces such as SASI and SCSI. Most of these upgrades were accomplished through the use of daughter boards that plugged into existing IC sockets on the board, with the original IC either replaced by a more capable IC or placed into a socket on the daughter board.

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