MODCOMP
Encyclopedia
MODCOMP was a small minicomputer
vendor that specialized in real-time
applications. They were founded in 1970 in Fort Lauderdale, Florida
, and many of their early sales were for tracking and data collection from NASA
space probes. In the 1990s they 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 opcode
s 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 II operating system
supported fixed priority scheduling
in a single address space. 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.
The Modcomp IV was replaced in the 1980s by the Modcomp Classic.
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 http://www.modcomp.com/.
Minicomputer
A minicomputer is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems and the smallest single-user systems...
vendor that specialized in real-time
Real-time computing
In computer science, real-time computing , or reactive computing, is the study of hardware and software systems that are subject to a "real-time constraint"— e.g. operational deadlines from event to system response. Real-time programs must guarantee response within strict time constraints...
applications. They were founded in 1970 in Fort Lauderdale, Florida
Fort Lauderdale, Florida
Fort Lauderdale is a city in the U.S. state of Florida, on the Atlantic coast. It is the county seat of Broward County. As of the 2010 census, the city had a population of 165,521. It is a principal city of the South Florida metropolitan area, which was home to 5,564,635 people at the 2010...
, and many of their early sales were for tracking and data collection from NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
space probes. In the 1990s they 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
Memory management unit
A memory management unit , sometimes called paged memory management unit , is a computer hardware component responsible for handling accesses to memory requested by the CPU...
, a two-stage pipelined CPU, and a floating point unit
Floating point unit
A floating-point unit is a part of a computer system specially designed to carry out operations on floating point numbers. Typical operations are addition, subtraction, multiplication, division, and square root...
.
The core architecture of the smaller machines included blocks of uncommitted opcode
Opcode
In computer science engineering, an opcode is the portion of a machine language instruction that specifies the operation to be performed. Their specification and format are laid out in the instruction set architecture of the processor in question...
s 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
VAX
VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs...
, although the address space
Address space
In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity.- Overview :...
per process
Process (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...
was limited to 64K 16-bit words; 256 pages of 256 words each, from the perspective of the MMU
Memory management unit
A memory management unit , sometimes called paged memory management unit , is a computer hardware component responsible for handling accesses to memory requested by the CPU...
.
The MAX II operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
supported fixed priority scheduling
Fixed priority pre-emptive scheduling
Fixed-priority pre-emptive scheduling is a scheduling system commonly used in real-time systems. With fixed priority pre-emptive scheduling, the scheduler ensures that at any given time, the processor executes the highest priority task of all those tasks that are currently ready to execute.The...
in a single address space. 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
Address space
In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity.- Overview :...
for each process
Process (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...
. Demand paging
Demand paging
In computer operating systems, demand paging is an application of virtual memory. In a system that uses demand paging, the operating system copies a disk page into physical memory only if an attempt is made to access it...
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.
The Modcomp IV was replaced in the 1980s by the Modcomp Classic.
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
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
's VAX
VAX
VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs...
and Alpha
DEC Alpha
Alpha, originally known as Alpha AXP, is a 64-bit reduced instruction set computer instruction set architecture developed by Digital Equipment Corporation , designed to replace the 32-bit VAX complex instruction set computer ISA and its implementations. Alpha was implemented in microprocessors...
systems continued to grow. The company successfully survives today as a systems integrator http://www.modcomp.com/.
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 http://www.cs.uiowa.edu/~jones/modcomp/.