Editing ICL VME (section)

===Series 39===
The [[ICL Series 39|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 [[computer cluster|cluster]] design. Each machine consists of a number of [[node (networking)|nodes]], and each node contains its own order-code processor (CPU) 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, 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.
<!-- if we're going to talk about public/global/nodal/local segments, we ought to explain them. Is this detail necessary? - MHK The nodal segments approach was leading edge and perhaps novel at the time, and would be worth describing I think - RW -->