ICT 1900 series facts for kids

ICT 1900 was a family of mainframe computers. These powerful machines were made by a British company called International Computers and Tabulators (ICT), and later by International Computers Limited (ICL). They were released in the 1960s and 1970s. The 1900 series was special because it was one of the few computers from outside America that could compete with IBM's famous System/360. It was very successful in Europe and the British Commonwealth countries.

How the ICT 1900 Computers Started

In 1963, a company called ICT was looking to buy another computer business from Ferranti. To make the deal more appealing, Ferranti showed ICT a special computer called the Ferranti-Packard 6000 (FP6000). This computer was designed by their Canadian team.

The FP6000 was a very advanced design for its time. It could even handle multiprogramming, which means running several programs at once. ICT thought about using the FP6000 as a base for their medium-sized computers.

The initial 1900 range did not suffer from the many years of careful planning behind the IBM 360.
-- Virgilio Pasquali

Then, in April 1964, IBM announced its new System/360 series. This was a family of computers that could all work together, covering many different customer needs. ICT knew they needed a strong answer to this.

They had two main choices:

• Develop their own computers based on the FP6000.
• Work with another company, RCA, who were making computers similar to IBM's System/360.

The FP6000 was already working, while RCA's computers would take years to be ready. So, ICT decided to go with the FP6000 design. The main computer in their new series was the ICT 1904. It was a version of the FP6000 but with ICT's own way of connecting other devices.

For bigger, more powerful computers, ICT developed the 1906. For smaller customers, they made the 1901, 1902, and 1903. These smaller machines were based on existing designs.

On September 29, 1964, the ICT 1900 range was officially announced. Just a week later, two working systems were shown at an exhibition in London.

The first ICT 1900 computer was sold in 1964 to the Morgan Crucible Company. It was a 1902 model with 16,000 words of memory and various other equipment. The very first system to be delivered was a 1904 model, which went to the Northampton College of Advanced Technology in January 1965.

How the 1900 Computers Worked

The ICT 1900 computers used a special way of storing and finding information called "word-addressing." They had eight special storage areas called "accumulator registers." Think of these as quick scratchpads for the computer to do its work. Three of these could also be used as "index registers" to help find data.

Each piece of information, or "word," was 24 bits long. This could hold four characters, like letters or numbers. The computers could also copy single characters.

A cool feature was that these computers could run many programs at the same time. Each program had its own protected memory space. This was controlled by special "datum" and "limit" registers. This meant one program couldn't accidentally mess with another program's data. Later models even added "paging" hardware, which allowed for "virtual memory." This made it seem like the computer had more memory than it actually did.

The original computers could use up to 32,000 words of memory. Later models could handle much more, up to 4 million words.

A big change from the original FP6000 was that the 1900 series used ICT's standard way of connecting other devices. This meant you could connect any ICT device, like a printer or a tape drive, to any computer in the series. This made it easy for owners to upgrade their computers without having to buy all new devices.

All input and output (like reading from a keyboard or printing) was handled by a special program called the "executive." User programs would ask the executive to do these tasks for them. This made sure everything ran smoothly and safely.

On smaller computers in the series, some complex tasks, like "floating-point" math (used for very precise calculations), were also handled by the executive. This meant that all computers in the series, big or small, could run the same programs.

If a computer had a "floating-point unit" (a special part for math), it could work on its own. This meant the computer could do other things while the math unit was busy, making it faster.

How Data Was Stored

The 1900 computers could handle different types of data:

• Characters: A 24-bit word could store four characters.
• Numbers: They could store single-length numbers (24 bits) or multi-length numbers for bigger calculations.
• Floating-point numbers: These were used for very precise numbers, like those in science. They came in single, double, and even quadruple lengths for super-high precision.

Character Sets

The ICT 1900 used a 6-bit character system, which meant it could only show 64 different characters. This usually meant only uppercase letters and no special control characters.

To handle more characters, like those in ASCII (which has 128 characters), they used a system of "shifts." For example, a special "alpha" shift character would mean the following characters were uppercase. A "beta" shift meant lowercase, and a "delta" shift meant the next character was a control character.

The 1900 used a version of ASCII called the ECMA character set. It was mostly the same but had a few differences in some symbols, like using `£` instead of `$`.

Different Models of the 1900 Series

The ICT 1900 series had many different models over the years, each with improvements.

Early Models

The first computers in the series included:

• ICT 1901: A very small computer. It was a big success because it was a good answer to IBM's smaller computers.
• ICT 1902 and 1903: Small machines. The 1903 was faster than the 1902.
• ICT 1904 and 1905: These were based on the original FP6000 design. The 1905 had a special unit for faster math.
• ICT 1906 and 1907: These were new, more powerful computers. The 1907 had a floating-point unit.
• ICT 1909: This was like the 1905 but slower and cheaper, designed for universities.

The speed of these computers varied a lot. A simple addition could take from 2.5 microseconds on a fast 1906 to 34 microseconds on a slower 1901.

Most machines were controlled using a special Teletype Model 33 machine, which allowed commands to be typed. The smallest 1901 was operated using switches on the computer itself.

Many different devices could be connected, like machines that read and punch cards or paper tape, and line printers. Data could be stored on magnetic tape and, starting in 1966, on Magnetic disks.

The 1900 E/F Series

In 1968, ICT released the E series. These were improved versions of the earlier models. For example, the 1906E was actually two 1904E processors working together to be faster.

Later, the F series improved these machines even more by using faster memory.

(It's important to know that ICT merged with another company in 1968 to form ICL. So, many of these E series computers were delivered with ICL badges.)

The 1900 A Series

In 1969, the 1900 A series came out. These computers used newer, faster electronic parts called "integrated circuits." This made them more powerful.

With the A series, the special math unit (floating point unit) became an optional add-on for all machines. This meant you didn't need a different model number just for that feature.

Higher-end machines like the 1904A and 1906A got a "paging unit." This allowed them to use a new operating system called GEORGE 4, which used "virtual memory" to manage programs more efficiently.

The 1900 S Series

In 1971, ICL announced the S series. These computers used even faster "semiconductor memory" instead of the older "core store." The top-of-the-line 1906S used super-fast "plated wire memory."

The 1904S, delivered in 1972, was 30% faster due to new logic circuits. This model was even used for computer animation in the famous movie Alien!

The 1900 T Series

As newer, bigger computers were being made, the smaller 1900 models started to seem old. To keep them competitive, new T series models were released. Each T model was based on a faster model from the previous series. For example, the 1903T was based on the 1904S.

These T series machines often had things like disk controllers built right into the computer cabinet to save space.

Computers That Worked Like the 1900

Over time, other computers were made that could run the same programs as the ICT 1900 series. These were sometimes made by ICL itself or by other companies.

ICL 2903/2904

IBM released a new small computer in 1969, which started to take sales away from ICL's smaller 1901 and 1902 models. To fight back, ICL created the 2903 and 2904 in 1973. Even though they had a new number, these computers used the 1900's instructions and could run 1900 software. They were a big success, with almost 3,000 machines sold.

ME29

The ME29 was another computer that could run 1900 programs. It was much faster than the original ICT 1904.

Odra 1300 Series

The Odra 1300 series were computers built in Poland between 1971 and 1978. They were designed to be compatible with the 1900 series. Because of an agreement with ICL, these Odra machines could run the standard ICL software.

ICL 2900 (New Range) Systems

Later, ICL's even newer computers, like the 2960, could also run 1900 series programs. They did this by using a special "emulation" mode. This was similar to how "virtualization" software works today, allowing one computer to pretend to be another.

Operating Systems

An "operating system" is the main software that manages a computer's hardware and software resources. It's like the conductor of an orchestra, making sure everything works together.

Executive

The first operating system for the FP6000 (which the 1900 was based on) was called "operators executive." It was simple but powerful for its time. It let the operator load programs, assign devices, and set priorities for programs.

Executive handled all the input and output for user programs. It also allowed programs to use memory efficiently. Because of special hardware, programs couldn't access each other's memory, which made the system very stable.

Different versions of Executive were made for the various 1900 models. Their main job was to make all the different computers seem the same to programs. This meant that a program written for one 1900 model could run on any other 1900 model, even if the hardware was different.

When magnetic disks became available, Executive became more complex. It helped manage files on the disk, so users didn't need to know exactly where their files were stored.

GEORGE

In 1964, ICT started developing a new operating system called GEORGE. The name partly came from George E. Felton, a key person in the programming division.

• George 1 was a simple system for running jobs one after another (called "batch processing"). You would feed in job instructions, and the computer would run them.
• George 2 added "spooling." This meant jobs and data were first read onto a disk. Then, the computer would process them, writing the results to disk. Finally, the results would be printed. This made the computer work more efficiently.
• George 3 was a complete operating system on its own. It could do both batch processing and "Multiple Online Programming" (MOP), which meant people could use the computer interactively from terminals.
• George 4 was introduced with the newer computers that had "paging" hardware. It used "virtual memory" to manage programs even better.

Programming Languages

ICT provided several ways to write programs for the 1900 series.

• PLAN: This was an "assembly language," which is a low-level language very close to how the computer thinks.
• The "Big Three" High-Level Languages: These were easier for humans to understand:

* ALGOL 60 * COBOL (often used for business programs) * FORTRAN 66 (often used for scientific and math programs)

Over time, these "compilers" (programs that turn human-written code into computer instructions) became more advanced. They started by using paper tape and cards, then magnetic tape, and finally disk files.

Other languages available included:

• NICOL: A simple language for creating reports, often used on smaller 1900 computers.
• JEAN: A language similar to BASIC, used for interactive conversations with the computer.
• SOBS: The Southampton BASIC System.
• Pascal: A popular language for teaching computer science.
• FORTRAN 77: An updated version of FORTRAN.
• BCPL: A language that was an early ancestor of the popular C programming language.

Software Applications

Many useful programs came with the ICT 1900 systems. These included the compilers (for programming languages) and utility programs (for managing files and other tasks). Other specialized software could be bought separately.

Some examples of application software included:

• SCAN: A system for managing stock and inventory.
• PERT: A system for managing projects.
• PROSPER: A system for financial planning.
• NIMMS and PROMPT: Systems for controlling production in factories.
• COMPAY: A program for company payroll.
• DATADRIVE and DATAVIEW: Systems for entering and looking up data online using many terminals.
• FIND: A program for analyzing data.
• Filetab: A tool for creating reports based on "decision tables." It was very flexible and could handle files. It was known for helping programmers write programs quickly.