Glenn’s Computer Museum

IBM System/360 9020 Air Traffic Control Console

The IBM 9020 system was a specially configured multiprocessor system that was used as the main FAA air traffic control computer from 1971 until the early 1990's. It was installed at the 20 FAA regional ARTCCs (Air Route Traffic Control Centers). Unlike standard IBM mainframes of the day, the 9020 was programmed to operate in "real time": that is, to compute and generate results as fast as or faster than data were fed into it. A full 9020 system consisted of six System/360 mainframes coupled to air traffic controllers' consoles, with data fed into the system from long-range radar and other ground stations. The six System/360 mainframe computers were connected together in a highly redundant and reliable multiprocessing configuration with special I/O capabilities (such as attaching radar consoles) not found in the standard System/360's. Only 25 9020 systems were ever built.

Early 9020 versions used System/360 Model 50 processors for all six processors, but our console comes from the latest 9020E version which used three Model 65's for "compute elements" and three Model 50's for "I/O control elements". Our control console is from one of the Model 65 computers, and is slightly different than the standard Model 65 console.

A quick deviation to discuss the IBM System/360. While technically obsolete now, the introduction of the System/360 family was a seminal event in computer evolution. The instruction set architecture was the most modern for its day and had many influences on current architecture (such as 8-bit bytes and 32-bit words). It also introduced a new I/O approach: a high-performance and programmable "channel" that could attach a vast and diverse set of I/O devices. The most significant feature was the concept of a family of computers, all having the same instruction architecture but with different performance and capacities, and all using the same I/O devices. Initially six models were announced: the Model 30, the Model 40, the Model 50, the Models 60 and 62, and the Model 70. These covered a performance range of about 100:1 and ranged from microprogrammed eight-bit datapath to hardwired 64-bit datapath. Yet they all ran the same software and used the same physical I/O devices.

Another eight model types were delivered during the System/360's lifetime, including the highly influential Model 67, Model 85, and Model 91. As a result of the technical features and especially the scalability and software compatibility across the family, the System/360, and its follow-ons such as the System/370 family, dominated the mainframe business.

The 9020 system had an abnormally long lifetime; the corresponding System/360 commercial products were withdrawn from sales in 1977, but the 9020 lingured in use until the early 1990's. One reason for this long life is the fact that much of the air traffic control application was written in System/360 assembly language. Another factor is the 9020's specialized radar console interfaces. As an example of the 9020 staying power, here's a scary NTSB report from 1996 about ARTCC outages pointing out that some of the ARTCCs are still using the 9020's at late as 1995! This reports discusses problems such as aging components where "replacements can be obtained only by scavenging parts from the [FAA] training computer". Thirty years is a long time for any complex equipment to remain functional, but in the world of computing technology, thirty years is many many generations of architecture and technology. Consider, as one example, that the 9020's used magnetic core memory and that a Model 65's performance was less than 1 MIPS!