Why a glossary?

Rather than repeatedly explain the meanings of various acronyms and initialisms, it was thought useful to include them separately, and link them as required.

DFC

Another name for the FPC.

ECP

Engineer's Control Processor. This was used for running diagnostics, and also for initiating IPL.

EMAS

The Edinburgh Multi-Access System. EMAS was an operating system written at the University of Edinburgh, originally for the English Electric System 4 (a near clone of the IBM 360/370 series). It was ported to the ICL 2900 series, and later on to the newer IBM mainframes. For more details, see the Wikipedia article, and also my talk about it.

FPC

File Peripheral Controller. The disk controller. It was attached to a trunk on the SAC, and provided (typically) eight streams to which a disk drive could be attached.

GPC

General Peripheral Controller. The controller to which most peripherals (OPER, printer, card reader, card punch, paper tape station, etc.) were attached. It connected to a trunk on the SAC.

Image store

The ICL 2900 architecture included instructions for accessing image store. These instructions were quite restricted (basically just 'read' and 'write'). The image store looked like a special kind of memory, but changes in its contents were used to modify the behaviour of the machine, and for accessing peripheral controllers. Image store instructions can be thought of as a mixture of access to machine control registers, and as input/output instructions (with image store addresses being analogous to input/output port numbers).

IPL

Initial Program Load. The act of loading a small program into a computer, which then loads a larger one, and eventually the operating system. More commonly known as bootstrapping or booting.

OCP

Order Code Processor. Machines in the ICL 2900 series were built from a series of components; usually, each was in a separate cabinet (or several cabinets in many cases). The OCP was what is normally called a CPU - it was the component that executed instructions (the order code), and did not include peripheral controllers, memory, etc.

OPER

OPERator station. Conventionally, these had two screens, and there could be several stations in a large machine room. There were also single screen versions, with or without a keyboard.

PSU

Power Supply Unit. Power supply units usually convert mains power into a form suitable for powering computer components. Large computers may have several different ones, powering different components.

VM

Shorthand for virtual machine.

SAC

Store Access Controller. This was specific to P-series systems. It can be thought of as an autonomous I/O controller, connecting the SMAC (via a SMAC port) to the various device controllers. These connection points were known as trunks.

SFL

System Function Language. This was the marketing name for the assembly language for the 2900 series.

Slave

This is essentially the ICL term for a cache, used both for memory access and items such as page table entries.

SMAC

Store Multiple Access Controller. This was the central connection point on P-series machines, with four (or occasionally more) ports to which a SAC or an OCP would be connected. More importantly, the SMAC contained the system memory (or store. Depending on model, there could be multiple SMACs in parallel.

VME/B

Virtual Machine Environment B. This was the mainstream operating system for the 2970 and above. It was later renamed to VME, and then to OpenVME, mainly for marketing reasons.

VME/K

Virtual Machine Environment K. VME/K was an operating system for smaller machines in the ICL 2900 series. It was introduced as an alternative to the mainstream operating system, VME/B, because the latter was too big and slow on the smaller machines. However, its life was short, and it was retired in the early 1980s due to cost cutting and internal politics.