Page 86 - Computer_Science_F5

(a) Arithmetic and logical operations privileged and non-privileged. These
(ADD, SUB, AND, OR): Performing include;
calculations on data in registers is a (a) Security: Prevents user programs
fundamental task for any program. from causing system crashes or Chapter One: Computer architecture

(b) Data transfer instructions (MOV, security breaches by restricting
FOR ONLINE READING ONLY
LEA): Moving data between access to sensitive hardware and
registers and memory locations is resources.
essential for program logic and data
manipulation. (b) Stability: Ensures the operating
(c) Register-to-register operations system maintains control of essential
(CMP, TEST): Comparing and resources, promoting overall system
testing register values are crucial stability.
for control flow and decision-making (c) Organisation: Provides a structured
within programs. environment for program execution,
There are several benefits of allowing for efficient resource
separating instructions into management and multitasking.

Exercise 1.18

(a) Complete the following privileged instructions (x86) given real-world kitchen
equivalents.

Table 1.17: Privileged instructions (x86) and real-world kitchen equivalents

Instruction Kitchen equivalent

Changing the recipe book (Paging table): This instruction
modifies the Control Register (CR3), which acts like the head
chef’s master recipe book (paging table) in our analogy. It tells
the CPU where to find specific data in memory, similar to how
the chef uses the recipe book to locate ingredient instructions.
Tampering with this could lead to confusion and wasted
resources (ingredients).

Checking the oven temperature (input): This instruction reads a
byte of data from a port specified in the DX register and stores it
in the AL register. Imagine the DX register as the oven number,
and the AL register stores the current temperature reading. This
is like the cook checking the oven temperature using a special
thermometer (privileged instruction).

77
Student’s Book Form Five

Computer Science Form 5.indd 77 23/07/2024 12:33