computer science

ICL Series 39

ICL Series 39 is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand ICL Series 39 rather than just read about it. In short: The ICL Series 39 was a range of mainframe and minicomputer computer systems released by the UK manufacturer ICL in 1985. The original Series 39 introduced the "S3L" (whose corrupt pronunciation resulted in the name "Estriel") processors and microcodes, and a nodal architecture, which is a form of Non-Uniform Memory Access.

Key takeaways

ICL Series 39 belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect ICL Series 39 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of ICL Series 39 from memory before moving on to harder problems.

Reference excerpt

The ICL Series 39 was a range of mainframe and minicomputer computer systems released by the UK manufacturer ICL in 1985. The original Series 39 introduced the "S3L" (whose corrupt pronunciation resulted in the name "Estriel") processors and microcodes, and a nodal architecture, which is a form of Non-Uniform Memory Access.

Origins 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:

Series 39 "Estriel" systems (Series 39 Level 40 and above, including multinodes), which replaced previous mid-range and large processors from the 2900 range, and needed a full computer room environment Series 39 DM1 systems (up to Series 39 Level 30), which were intended to replace the smaller processors such as the ICT1901/2, the ICL2903/4 and the ME29 ranges. These brought mainframe class operating system facilities into the office environment, a first for ICL.

Design The original Series 39 introduced the "S3L" 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 1,000 metres (3,300 ft) 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. All Series 39 machines were supported by a set of waist height peripheral 'Cabinets' (connected via fibre optic cables via one or more Multi Port Switch Units or MPSU's) providing disk storage capabilities:-

Cabinet 2 - these were the main Disk Storage Cabinets holding a pair of 330Mb 8-inch "Swallow" Hard Drives Cabinet 3 - these were an expansion cabinet to the Cabinet 2 and could hold up to four more 330Mb 8-inch "Swallow" Hard Drives Cabinet 4 - these were a bridge cabinet would was used to connect Series 39 to older 2900 Diskpack based Storage (such as EDS200's) Cabinet 1 was the name given to the DM1 Series 39 Level 30 (and 20/15/25/35 variants) core system. All Series 39 machines also featured a Node Support Computer (NSC) hosted on their Storage Motherboards - this was x86 architecture and acted much like today's ILO or DRAC cards on HP/Dell Servers and allowed Support Staff to manage the Nodes remotely including the ability to completely stop and restart the main Nodes.

Evolution In the mid-1980s the Series 39 Level 30 was supplemented by a Level 20 variant which was a forcibly underclocked Level 30 (using wire links on a daughterboard). In the late 80s these were both replaced by Level 15, 25 and 35 variants which also carried various levels of clocking state but featured more memory than their predecessors and could also be fitted with Dual OCP and IOC motherboards for even more computing and I/O capability. The early 1990s saw upgrades to the Series 39 range. DX System products were introduced to replace the DM1 systems, appearing in product line-ups already in late 1991. The Essex project led to the introduction of the SX System products in 1990 to replace the Estriel ("S3L") systems. These machines featured a new "very sophisticated pipelined processor" design that provided support for the ICL 2900 order code by employing a low-level "implementation order code" known as Picode. Picode is comparable to microcode but operates at much higher level than microcode from earlier machines and at a slightly lower level than ICL 2900 instructions, operating within similar constraints to those applying to conventional machine instructions. Picode instruction sequences are fed into instruction pipelines and provide atomic results, being uninterruptable.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with ICL Series 39

Start with the simplest possible case. Write down what ICL Series 39 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to ICL Series 39 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about ICL Series 39 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of ICL Series 39

In research: ICL Series 39 appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses ICL Series 39 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: ICL Series 39 is common in secondary-school and first-year university syllabi. It links to neighbouring topics 32-bit computers, Computer-related introductions in 1985, Computing platforms, so understanding it makes those chapters shorter.
In everyday life: Look for ICL Series 39 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study ICL Series 39 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what ICL Series 39 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain ICL Series 39 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is ICL Series 39 in simple terms?

Why does ICL Series 39 matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study ICL Series 39?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on ICL Series 39.