computer science

Register–memory architecture

Register–memory architecture 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 Register–memory architecture rather than just read about it. In short: In computer engineering, a register–memory architecture is an instruction set architecture that allows operations to be performed on (or from) memory, as well as registers. If the architecture allows all operands to be in memory or in registers, or in combinations, it is called a "register plus memory" architecture.

Key takeaways

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

Reference excerpt

In computer engineering, a register–memory architecture is an instruction set architecture that allows operations to be performed on (or from) memory, as well as registers. If the architecture allows all operands to be in memory or in registers, or in combinations, it is called a "register plus memory" architecture. In a register–memory approach one of the operands for operations such as the ADD operation may be in memory, while the other is in a register. This differs from a load–store architecture (used by RISC designs such as MIPS) in which both operands for an ADD operation must be in registers before the ADD. Example of Load-Store (RISC)

;Add mem1 to mem2 mov r1, [mem1] ; Load first value into register mov r2, [mem2] ; Load second value into register add r2, r1, r2 ; r2 = r1 + r2 mov [mem2],r2 ; Store result

Example of register-memory (CISC) Some register-memory machines cannot write ALU results to memory, only their registers. This is like an accumulator machine with multiple accumulators:

;Add mem1 to mem2, if add-register-to-memory instructions are not supported mov r1, [mem1] ; Load first value into register add r1, [mem2] ; Add second value into register mov [mem2], r1 ; Store result

Some register-memory machines are able to write ALU results directly to memory, saving an instruction:

;Add mem1 to mem2, if add-register-to-memory instructions are supported mov r1, [mem1] ; Load first value into register add [mem2],r1 ; Add it to second value

Example of register plus memory (CISC)

;Add mem1 to mem2 add [mem2],[mem1] ; Add first to second value

An example of register-memory architecture that can write ALU results to memory is the Intel x86. Examples of register plus memory architecture are:

IBM System/360 and its successors, which support memory-to-memory fixed-point decimal arithmetic operations, but not binary integer or floating-point arithmetic operations; PDP-11, which supports memory (or register) source and destination operands for most two-operand integer operations; VAX, which supports memory or (or register) source and destination operands for binary integer and floating-point arithmetic; Texas Instruments MSP430 is a rare microcontroller that supports memory (or register) source and destination operands for all 24 of its two-operand operations. Motorola 68000 series can move data memory-to-memory with nearly all addressing modes. All other integer arithmetic/logic operations require at least one parameter to reside in a register, making it primarily a register-memory machine.

See also Load–store architecture Addressing mode

References

Worked examples

Example 1 — a first encounter with Register–memory architecture

Start with the simplest possible case. Write down what Register–memory architecture 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 Register–memory architecture 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 Register–memory architecture 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 Register–memory architecture

In research: Register–memory architecture 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 Register–memory architecture 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: Register–memory architecture is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer architecture, so understanding it makes those chapters shorter.
In everyday life: Look for Register–memory architecture 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 Register–memory architecture in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Register–memory architecture 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 Register–memory architecture out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Register–memory architecture in simple terms?

Why does Register–memory architecture 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 Register–memory architecture?

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 Register–memory architecture.