Hardware
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.
It was possible to upgrade the memory to 256 KB, which was extremely large for the time. While not directly supported by CP/M, the extra memory could be used to implement a ram disk, caching of the operating system image (to greatly improve warm boot time), or a print spooler.
The Big Board II (1982) incorporated many of the most popular upgrades for the original Big Board into its design. It also featured a small breadboard area that allowed for many simple upgrades to be performed without the addition of daughter boards.
Read more about this topic: Ferguson Big Board
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