computer science

Virtual Machine Communication Facility

Virtual Machine Communication Facility 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 Virtual Machine Communication Facility rather than just read about it. In short: The IBM Virtual Machine Communication Facility (VMCF) is a feature of the VM/370 operating system introduced in Release 3 in 1976. It "provides a method of communication and data transfer between virtual machines operating under the same VM/370 system." VMCF uses paravirtualization through the diagnose instruction VMCF SEND function to send data, in blocks of up to 2048 bytes, from one virtual machine to another.

Key takeaways

Virtual Machine Communication Facility 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 Virtual Machine Communication Facility to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Virtual Machine Communication Facility from memory before moving on to harder problems.

Reference excerpt

The IBM Virtual Machine Communication Facility (VMCF) is a feature of the VM/370 operating system introduced in Release 3 in 1976. It "provides a method of communication and data transfer between virtual machines operating under the same VM/370 system." VMCF uses paravirtualization through the diagnose instruction VMCF SEND function to send data, in blocks of up to 2048 bytes, from one virtual machine to another. The receiving virtual machine accesses the data thru the diagnose RECEIVE function. It provides a simpler interface and greater performance than the prior use of virtual channel-to-channel adapters for the same purpose. VMCF was superseded by the Inter User Communication Vehicle (IUCV), introduced in 1980 with VM/SP.

References

External links Date, Shashank Prabhakar (1986). "A multi-tasking hierarchical file system for VM/CMS using virtual machine communication". University of Houston. Retrieved March 30, 2025. Faconti, G; Santoro, N. "APL106 VSAPL Virtual Machine Communication Facility Auxiliary Processor" (PDF). Consiglio Nazionale della Ricerche. Retrieved Mar 30, 2025. Jensen, R.M. (March 1979). "A formal approach for communication between logically isolated virtual machines". IBM Systems Journal. 18 (1): 71–92. doi:10.1147/sj.181.0071. Retrieved March 30, 2025.

Worked examples

Example 1 — a first encounter with Virtual Machine Communication Facility

Start with the simplest possible case. Write down what Virtual Machine Communication Facility 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 Virtual Machine Communication Facility 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 Virtual Machine Communication Facility 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 Virtual Machine Communication Facility

In research: Virtual Machine Communication Facility 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 Virtual Machine Communication Facility 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: Virtual Machine Communication Facility is common in secondary-school and first-year university syllabi. It links to neighbouring topics IBM mainframe operating systems, Software stubs, VM (operating system), so understanding it makes those chapters shorter.
In everyday life: Look for Virtual Machine Communication Facility 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 Virtual Machine Communication Facility in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Virtual Machine Communication Facility 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 Virtual Machine Communication Facility out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Virtual Machine Communication Facility in simple terms?

Why does Virtual Machine Communication Facility 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 Virtual Machine Communication Facility?

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 Virtual Machine Communication Facility.