Modcomp

MODCOMP (Modular Computer Systems, Inc) was a small minicomputer vendor that specialized in real-time applications. They were founded in 1970 in Fort Lauderdale, Florida. In the 1970s and 1980s, they produced a line of 16 and 32-bit mini-computers. Through the 1980s, MODCOMP lost market share as more powerful micro-computers became popular, and Digital Equipment Corporation's VAX and Alpha systems continued to grow. The company successfully survives today as a systems integrator.

Their first computer was the 16-bit MODCOMP II, introduced shortly after the company was founded. This had 15 general-purpose registers, and was initially offered with a 16-kilobyte, 18-mil magnetic core memory with an 800ns cycle time, expandable to 128 kilobytes. The MODCOMP I followed for smaller applications, with only 3 general-purpose registers and a maximum of 64 kilobytes of core. The MODCOMP III, introduced in 1972, maintained compatibility with the Modcomp II, while using newer technology such as LSI, where the earlier machines had used SSI/MSI technology.

to remain 100% compatible with the MODCOMP III, which had used  and . Many of MODCOMP's early sales were for tracking and data collection from NASA space probes, and in the 1980s they provided a network of 250 MODCOMP II systems to control the Space Shuttle launch complex at Cape Canaveral until T-30, at which point control was handed over to a single IBM mainframe. In the 1990s MODCOMP developed a product in the UK called ViewMax, which was used to connect web-based "front-ends" to legacy systems. In 1996, MODCOMP had $36.7 million in sales, and were purchased by CSPI.

In the 1970s and 1980s, they produced a line of mini-computers. The MODCOMP I, II and III were 16-bit machines, while the MODCOMP IV was an upward compatible 32-bit machine with a paged memory management unit, a two-stage pipelined CPU, and a floating point unit. The core architecture of the smaller machines included blocks of uncommitted opcodes and provisions for physical modularity that hint at the reasoning behind the company name. In many regards, the MODCOMP IV had potential as a competitor for the VAX, although the address space per process was limited to 64K 16-bit words; 256 pages of 256 words each, from the perspective of the MMU.

The MAX III operating system supported fixed priority scheduling in a single address space. (MAX was an acronym for Modular Application eXecutive.) The MAX IV operating system was largely compatible, while it took advantage of the new features of the MODCOMP IV to allocate one address space for each process. Demand paging was not supported, and swapping was used when the total memory demand for all processes exceeded the available physical memory.

Outside of NASA, these systems were particularly popular with the oil industry, both in oil refineries and in oilfields, and for general manufacturing automation. Standard Oil, in particular, made extensive use of Modcomp equipment in the 1970s, as documented, for example, in US Patents 3,968,487, 4,005,387 and 4,320,452.

Beginning in 1978, the MODCOMP IV was replaced by the MODCOMP Classic; the first Classic model was the 7810. This retained compatibility with the MODCOMP IV, but offered full support for 32-bit addressing. The successor to MAX IV, developed to fully exploit this system, was called MAX 32. Both 16-bit and 32-bit applications could run on the new 9250 and 9260 computers.

Through the 1980s, MODCOMP lost market share as more powerful micro-computers became popular, and Digital Equipment Corporation's VAX and Alpha systems continued to grow. The company successfully survives today as a systems integrator [1].

External links

• A collector has posted photographs of a MODCOMP II.
• Another collector has posted photos of a larger Modcomp II (near the bottom of the page).
• Levins Technologies, Inc. has photos of MODCOMP Classic Systems
• A third-party programmer's pocket reference card for the MODCOMP IV is available [2].