create the next generation and leave the previous generation intact; this program however is deliberately choosing to create generation 101, to identify a public release. Enhanced security variants As a result of ICL's heavy involvement with delivery of computer services to the UK Public Sector, in particular those with special security requirements such as OPCON CCIS, it was an early entrant into the market for Secure Systems. VME formed a core of ICL's activities in the Secure Systems arena. It had the advantage that as the last large-scale operating system ever designed, and one built from scratch, its underlying architecture encompassed many of the primitives needed to develop a Secure System, in particular the hardware assisted Access Control Registers (ACR) to limit to privileges that could be taken by any process (including Users). This led to the UK Government's Central Computing and Telecommunications Agency (CCTA) funding Project Spaceman in the mid 1980s for ICL Defence Technology Centre (DTC) to develop an enhanced security variant of VME. ICL launched this as a pair of complementary products, with the commercial release being called High Security Option (HSO), and the public sector release, including Government Furnished Encryption (GFE) technologies, being called Government Security Option (GSO). HSO and GSO were formally tested under the CESG UK (Security) Evaluation Scheme, one of the predecessors to ITSEC and Common Criteria, and in doing so became the first mainstream operating system to be formally Certified. Series 39 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 (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. Development process VME was originally written almost entirely in S3, a specially-designed