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Date November 2020 Marks available 1 Reference code 20N.1.SL.TZ0.4
Level SL Paper 1 Time zone no time zone
Command term State Question number 4 Adapted from N/A

Question

The machine instruction cycle is a sequence of actions that a central processing unit (CPU) performs to execute each machine code instruction in a program.

State where the program is held.

[1]
a.

State the part of the central processing unit (CPU) that performs the decoding.

[1]
b.

Outline the function of the memory address register (MAR).

[2]
c.

Markscheme

Award [1 max].
RAM;

a.

Award [1 max].
CU/Control Unit;

b.

Award [2 max].
MAR (is a register in the CPU that) stores the address of the (next) instruction/data;
to be read from/written to RAM;

c.

Examiners report

A small number of candidates recognised that a program is held in random access memory (RAM) when it is being run. However, a large number of candidates gave less precise or incorrect answers, such as 'in the computer' or 'on the drive'.

a.

Many candidates correctly identified the control unit as the part of the central processing unit (CPU) that decodes instructions. Some candidates incorrectly stated the ALU or the CPU, the latter being taken from the question.

b.

A good range of answers was seen for this question with candidates recognising that the memory address register stores the address of the data to be read from or written to the RAM. Candidates who gave a correct answer either achieved one or both marks, depending on whether they covered part or all of the answer.

c.

Syllabus sections

Topic 2: Computer organization » 2.1 Computer organization
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Topic 2: Computer organization

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