MicroVAX II

Introduction
The MicroVAX II was one of the most popular computers ever sold. The success of the MicroVAX II set the course of development for the VAX chip family for the rest of the 1980s. The MicroVAX II was the system that put the VAX CPU on a chip. With powerful VAX virtual memory, 32-bit computing power, and software compatibility across all VAX processors, the MicroVAX II micro system provided functionality and flexibility that was unparalleled in the industry. From hereon all subsequent VAXes would be on a chip.

MicroVAX sold 20,000 units in its first year.

"The sense I always had was that there were four key technical visionaries at the beginning of MicroVAX: Dave Cutler, with his creation of the MicroVAX I system for early software development; Bob Supnik, who headed up MicroVAX chip development and also wrote the microcode; Jesse Lipcon who headed up MicroVAX II Server Development; and Dick Hustvedt, who drove the MicroVMS Software Strategy." Jay Nichols, DEC Computer Special Systems, Manager of Engineering

My personal experience with this computer dates back to CAE Electronics, in the late 1980s which used numerous MicroVAX IIs in their flight simulators and software development. At the time I was working on GOULD SEL-32 series of 32 bit computers. The SEL computers were basically green screen terminal accessible technically updated clones of the IBM 360 architecture and used for real-time simulation. I had a chance to do work on a visual driver for a VAX based simulation. I happened to find a spare MicroVAX II to use for a couple of hours to debug my code. I was in awe as to how easy it was to use the DECWindows interface and the FORTRAN debugger on the VAXStation. By comparison, our SEL computer had no X-Windows capability and we were relegated to debug our code the old fashion way; by putting breakpoints into the code. Our VAX developers were really spoiled by the features and DECWindows interface provided by the VMS operating system.

When I joined Scotia McLeod, a Bay Street brokerage firm, in the 1990s, I found it to be a large VAX shop. Sure enough there were a couple of MicroVAX II computers named GREEN and RED. These small systems supported a community of several developers through DEC VT series terminals connected through LAT terminal servers. Only several years later were these replaced by DECWindows based VAX4000VLCs on each developer's desktop. Code on these smaller systems was written, compiled and moved to the firm's larger VAX8000 series production system.

One day it was decided that our corporate standard for databases would be Oracle on SUN Solaris and not the VAX based Ingres then in use. As a DBA, I found Ingres to be a perfectly stable database. As well, the VMS operating system was very stable and our production systems ran without issue. I was surprised that the company was shifting its strategy from VAX to Unix. At one of the management meetings with Oracle present, we were given an overview of the Oracle database. I asked the Oracle technical rep on what platform Oracle database development was done; the rep responded that it was written on VMS due to its better software development capabilities.

KA630 CPU
The MicroVAX II, code named Mayflower, was a mid-range MicroVAX introduced in May 1985. It ran VAX/VMS or, alternatively, ULTRIX, DEC's native Unix operating system. 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 co-processor operating at 5 MHz (200ns 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 1MByte 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.

The MicroVAX II was slow, especially when used with DECWindows, MFM disk drives and with many users on a single system. What made it seem a responsive system in it's day was that the VT terminals typically operated at 9600 baud and with that speed, many interactive sessions could be managed by one MicroVAX. However, a very simple option was to replace the KA630 CPU with a KA650 CPU. No other changes were needed, just a CPU swap that effectively tripled the CPU speed. I implemented such an upgrade on my own MicroVAX II and the response time difference is noticeable.

MicroVAX II SPECIFICATIONS

CPU CPU Module: KA630, UV2 no cache Number of Processors: 1 CPU Technology: NMOS (?) CPU Cycle Time: 200ns MEMORY Maximum Memory: 1MB on motherboard, can add up 16MB in 2,4,8, or 16MB cards (base 1MB disabled) (parity) I/O INTERFACES Ethernet: BNC 10MBit Q-Bus: Max 3.3 MBytes/s PERFORMANCE VUPS: 0.9 TPS: 7 NOTES: Can be made into a VAXStation II by adding VCB01 (QVSS), or a VAXstation II/GPX by adding VCB02 (QDSS).

MS630 Memory
Four variants of the MS630 existed:

• 1 MByte, MS630-AA
• 2 MByte, MS630-BA
• 4 MByte, MS630-BB
• 8 MByte, MS630-CA.

The MS630-AA was a dual-height module, whereas the MS630-BA, MS630-BB and MS630-CA were quad-height modules. These modules used 256 Kb DRAMs and were protected by byte-parity, with the parity logic located on the module. The modules connected to the CPU module via the backplane through the C and D rows and a 50-conductor ribbon cable. The backplane served as the address bus and the ribbon cable as the data bus.

Enclosures
The MicroVAX II came in three models of enclosure:

• BA23
• BA123
• 630QE desk side enclosure

Sources:

• netbsd.org
• >wikipedia.org