the VDUEB equipped Super-80. The VDUEB proved to be a popular modification, with a users' group forming for owners of VDUEB equipped computers - The "Super-80 VDUEB Users' Club". The Universal Floppy Disk Controller (UFDC) was an add-on floppy disk interface developed by Microcomputer Engineering (MCE). The UFDC was based on the Western Digital WD2793 floppy disk controller chip and had a Z80 DMA controller on board. The most popular disk format was 5" (133 mm) 80 track, double sided, double density using a Mitsubishi floppy drive mechanism. This gave a formatted disk capacity of 800kB. The UFDC's use of DMA required the VDUEB upgrade to be present. To install the disk controller, the Z80 CPU was removed from the main computer board and installed on the UFDC board. The UFDC then piggybacked on the socket vacated by the CPU. This meant that in theory, the UFDC could be used with almost any Z80 based system, provided there was enough physical space above the CPU. The UFDC used a primitive track based disk operating system called "Super-80 DOS", however a CP/M BIOS later became available. The MXB-1 Memory Expansion Board was designed by a member of the VDUEB Users' Club. The MXB-1 contained space for extra EPROMs, an optional battery backed real time clock, a centronics compatible printer interface and address decoding for up to 192kB of RAM. The extra RAM was installed by replacing the standard 4116 16k × 1 bit RAM chips with 4164 64k × 1 bit RAM chips. The CPU's 64kB address limit was worked around through bank switching. The MXB-1 was mostly of benefit to users running the CP/M disk operating system, since CP/M could then have a full 64kB of RAM for programs, with up to 128kB being used as a small RAM disk. The El Graphix "X-RAM" board provided up to 16K of battery backed CMOS RAM or EPROM. Several X-RAM boards could be piggybacked allowing each to be port selected as independent 16K banks of memory. This memory took the form of 8 x 2K 24pin sockets which accepted either 2016 CMOS RAM or 2716 EPROMS. As the system ROM shared part of the address range taken up by the X-RAM board the system ROM could be copied into CMOS RAM on the fly and modified as required to actively add or modify custom functions into the operating system. See also Dick