During the late 1970s and 1980s, Michael Foster and Ian Currie of the Royal Signals and Radar Establishment (RSRE) created the Flex Computer System in Malvern, England. It was developed for the safe and efficient construction of strongly typed procedures, and it employed a tagged storage method to achieve a capability architecture.

The operating system, (modular) compiler, editor, garbage collector, and file system were all written in ALGOL 68RS, and the hardware was bespoke and microprogrammable.

Flex was implemented utilizing hardware with editable microcode in (at least) two versions. Logica provided the first to an RSRE design, whereas ICL PERQ was employed in the second. Storage allocation, deallocation, and garbage collection were all handled by the microcode alone. This quickly eliminated a large class of problems caused by the intentional or unintentional misuse of pointers.

The tagged, write-once filestore was a standout feature of Flex. This enabled the transparent writing and retrieval of arbitrary code and data structures without external encodings. As a result, data may be safely transferred from one program to the next.

On the other hand, remote capabilities allowed data and operations on other computers to be accessible through a network connection without involving the application software in external encodings of data, parameters, or result values.

The entire approach allowed for the safe implementation of abstract data types. Data items and the processes required to access them could be linked together and the resultant capability transferred freely around. The capability would provide access to the procedures, but it couldn’t be utilized to get access to the data in any manner.

Another significant aspect of Flex was the concept of shaky pointers, sometimes known as weak references, which point to memory blocks that may be freed at the next trash collection. For example, this might be used to store cached disc blocks or a list of spare procedure work-spaces.

Along with Flex, COMFLEX, a packet switching network capable of transferring data at magnetic-disc speeds, was created. It allowed remote file storage, remote capabilities, and remote procedure calls to be used.

Download Flex Machine PNG images transparent gallery.