ICL Series 39

The ICL Series 39 was a range of mainframe and minicomputer computer systems released by the UK manufacturer ICL in 1985.

The Series 39 range was based upon the New Range concept and the VME operating system from the company's ICL 2900 line, and was introduced as two ranges:

The original Series 39 introduced the "S3L" (whose corrupt pronunciation resulted in the name "Estriel") processors and microcodes, and a nodal architecture (see ICL VME) which is a form of Non-Uniform Memory Access which allowed nodes to be up to 1000 metres apart.

The Series 39 range introduced Nodal Architecture, a novel implementation of distributed shared memory that can be seen as a hybrid of a multiprocessor system and a cluster design. Each machine consists of a number of nodes, and each node contains its own order-code processor and main memory. Virtual machines are typically located (at any one time) on one node, but have the capability to run on any node and to be relocated from one node to another. Discs and other peripherals are shared between nodes. Nodes are connected using a high-speed optical bus (Macrolan) using multiple fibre optic cables, which is used to provide applications with a virtual shared memory. Memory segments that are marked as shared (public or global segments) are replicated to each node, with updates being broadcast over the inter-node network. Processes which use unshared memory segments (nodal or local) run in complete isolation from other nodes and processes.

The semaphore instructions prove their worth by controlling access to the shared writable memory segments while allowing the contents to be moved around efficiently.

Overall, a well configured Series 39 with VME had an architecture which can provide a significant degree of proofing against disasters, a nod to the abortive VME/T ideas of the previous decade.

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