The MicroVAX is a discontinued family of low-cost minicomputers developed and manufactured by Digital Equipment Corporation (DEC). The first model, the MicroVAX I, was introduced in 1983. They used processors that implemented the VAX instruction set architecture (ISA) and were succeeded by the VAX 4000. Many members of the MicroVAX family had corresponding VAXstation variants, which primarily differ by the addition of graphics hardware. The MicroVAX family supports Digital's VMS and ULTRIX operating systems. Prior to VMS V5.0, MicroVAX hardware required a dedicated version of VMS named MicroVMS. MicroVAX I The MicroVAX I, code-named Seahorse, introduced in October 1984, was one of DEC's first VAX computers to use very-large-scale integration (VLSI) technology. The KA610 CPU module (also known as the KD32) contained two custom chips which implemented the ALU and FPU while TTL chips were used for everything else. Two variants of the floating point chips were supported, with the chips differing by the type of floating point instructions supported, F and G, or F and D. The system was implemented on two quad-height Q-bus cards - a Data Path Module (DAP) and Memory Controller (MCT). The MicroVAX I used Q-bus memory cards, which limited the maximum memory to 4MiB. The performance of the MicroVAX I was rated at 0.3 VUPs, equivalent to the earlier VAX-11/730. MicroVAX II The MicroVAX II, code-named Mayflower, was a mid-range MicroVAX introduced in May 1985 and shipped shortly thereafter. It ran VAX/VMS or, alternatively, ULTRIX, the DEC native Unix operating system. At least one non-DEC operating system was available, BSD Unix from MtXinu. It used the KA630-AA CPU module, a quad-height Q22-Bus module, which featured a MicroVAX 78032 microprocessor and a MicroVAX 78132 floating-point coprocessor operating at 5 MHz (200 ns cycle time). Two gate arrays on the module implemented the external interface for the microprocessor, Q22-bus interface and the scatter-gather map for DMA transfers over the Q22-Bus. The module also contained 1 MB of memory, an interval timer, two ROMs for the boot and diagnostic facility, a DZ console serial line unit and a time-of-year clock. A 50-pin connector for a ribbon cable near the top left corner of the module provided the means by which more memory was added to the system. The MicroVAX II supported 1 to 16 MB of memory through zero, one or two memory expansion modules. The MS630 memory expansion module was used for expanding memory capacity. Four