Computer Systems
What's covered
Key facts
Assemblers and Assembly Language
A program written in one CPU's assembly language is tied to that CPU architecture and won't run on a different one without being rewritten.
Boolean Algebra Simplification
Absorption rule: A + (A . B) = A and A . (A + B) = A.
Boolean Logic: AND, OR, NOT Gates
For inputs A=1 and B=0, A AND B = 0.
CPU Components: ALU, Control Unit, Registers
The accumulator (ACC) is the register that holds the data the ALU is currently working on and the result of the most recent ALU operation.
Classification of Programming Languages: High and Low Level
Assembly language is a low-level language: its instructions are mnemonics for the instruction set of one specific CPU architecture.
Embedded Systems
Assembly language is often used to develop software for embedded systems and for controlling specific hardware components.
Factors Affecting CPU Performance: Clock Speed, Cores, Cache
Adding cores does not always double performance because many programs cannot fully exploit parallel execution (Amdahl's law).
Hardware vs Software
The CPU is a hardware component (a physical silicon chip), not software.
Logic Circuits and Truth Tables
For Q = A AND (not B): with A=1, B=1, not B = 0, so Q = 1 AND 0 = 0.
Main Memory: RAM and ROM
Most computers need both: ROM holds the boot code so the machine can start up; RAM holds the running programs once the OS has loaded.
Practice questions with answers
A taste of the 171 questions in this topic, answers marked. Sign up to practise the full set with spaced repetition.
What does an assembler do?
- •Converts machine code into human-readable source code
- •Links compiled object files into an executable program
- ✓Translates assembly into machine code
- •Translates high-level code into assembly language
Using Boolean identities, what does A . 1 simplify to?
- •0
- •1
- ✓A
- •Ā
How many inputs does a NOT gate have?
- ✓Exactly one input
- •Exactly two inputs
- •Two or more inputs
- •Up to four inputs
What does ALU stand for?
- •Accumulator logic unit
- •Advanced logic unit
- •Arithmetic load unit
- ✓Arithmetic logic unit
Which is an example of a high-level language?
- •Assembly language tied to a specific CPU
- •Machine code made of binary instructions
- •Microcode hidden deep inside a processor
- ✓Python using readable English-like keywords
What is an embedded system?
- ✓A computer system with a dedicated function inside a larger device
- •A general-purpose computer that runs many user-chosen programs
- •A server that provides services to other computers on a network
- •A virtual machine that runs inside another operating system
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