Computer Systems

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1. CPU Architecture

1.1 Components of the CPU

The CPU (Central Processing Unit) is the brain of the computer. It processes data and executes Instructions.

Component	Function
Arithmetic Logic Unit (ALU)	Performs arithmetic (addition, subtraction) and logical (AND, OR, NOT) operations
Control Unit (CU)	Coordinates the activities of the CPU; fetches, decodes, and executes instructions
Cache	Small, fast memory inside the CPU that stores frequently used data
Registers	Small, fast storage locations within the CPU
Buses	Pathways for data transfer between components

The ALU in detail. The ALU is the part of the CPU that performs actual computation. Given two Binary inputs and an operation code (from the control unit), it produces a result and a set of Status flags (zero, negative, carry, overflow). For example, given inputs 0110 and 0011 with an “add” operation, the ALU outputs 1001 with a zero flag of 0 (result is non-zero).

The Control Unit in detail. The CU does not perform computation itself. Instead, it sends Control signals to other components: it tells the memory which address to read or write, tells the ALU which operation to perform, and tells the registers when to load or store values. It is the Conductor of the CPU orchestra.

1.2 Registers

Register	Function
Program Counter (PC)	Holds the memory address of the next instruction to be fetched
Memory Address Register (MAR)	Holds the address of the memory location to be read from or written to
Memory Data Register (MDR)	Holds the data that has been read from or is about to be written to memory
Accumulator (ACC)	Stores the results of calculations performed by the ALU
Current Instruction Register (CIR)	Holds the instruction currently being decoded and executed

Key distinction: The PC holds an address (where to go next). The MAR also holds an address (where to read/write data). The MDR holds the actual data (what was read or what Will be written). The CIR holds the instruction (what to do).

1.3 The Fetch-Decode-Execute Cycle

The CPU continuously cycles through three stages:

1. Fetch:

The address in the PC is copied to the MAR
The instruction stored at that address is copied from memory to the MDR
The PC is incremented (points to the next instruction)
The instruction in the MDR is copied to the CIR

2. Decode:

The control unit decodes the instruction in the CIR
It determines what operation to perform and what data to use

3. Execute:

The instruction is carried out (the ALU performs calculations, data is moved, etc.)
The cycle repeats

Detailed trace. Suppose the PC contains address 100, and memory address 100 contains the Instruction “ADD 5” (add 5 to the accumulator).

Fetch: MAR $\leftarrow$ 100 (copy PC to MAR). MDR $\leftarrow$ memory[100] (read instruction from address 100). PC $\leftarrow$ 101 (increment PC). CIR $\leftarrow$ “ADD 5” (copy MDR to CIR).
Decode: CU decodes “ADD 5” — this means add the value 5 to the accumulator.
Execute: ACC $\leftarrow$ ACC + 5 (ALU performs the addition, result stored in accumulator).

Worked Example. Trace the fetch-decode-execute cycle for a subtract instruction when PC = 50 and The instruction at address 50 is “SUB 3”.

Fetch: MAR $\leftarrow$ 50. MDR $\leftarrow$ memory[50] (“SUB 3”). PC $\leftarrow$ 51. CIR $\leftarrow$ “SUB 3”.
Decode: CU decodes “SUB 3” — subtract the value 3 from the accumulator.
Execute: ACC $\leftarrow$ ACC - 3. If ACC was 10, it is now 7.

1.4 Von Neumann Architecture

The Von Neumann architecture is the standard model for most computers:

Data and instructions are stored in the same memory
Memory is accessed sequentially
The CPU fetches, decodes, and executes instructions one at a time
A single bus is used for data transfer

The stored program concept. Before Von Neumann, computers were rewired for each new program. Von Neumann’s key insight was that programs and data could both be stored in the same memory, and the CPU could read instructions from memory just as it reads data. This means you can change what a Computer does by changing the contents of its memory — no rewiring required.

Von Neumann bottleneck. Because instructions and data share the same bus, the CPU cannot fetch An instruction and read/write data simultaneously. This limits performance. Modern processors Mitigate this with caches, pipelines, and Harvard-architecture elements within the CPU.

Von Neumann vs Harvard comparison:

Feature	Von Neumann	Harvard
Memory	Shared for data and instructions	Separate data and instruction memory
Bus	Single bus	Separate buses
Simplicity	Simpler hardware	More complex hardware
Performance	Bottleneck when fetching and data	Can fetch instruction and data simultaneously
Use	Most general-purpose computers	DSP, some microcontrollers

1.5 Buses (Higher Tier)

The bus system connects the CPU, memory, and I/O devices.

Address bus: Carries memory addresses from the CPU to memory (one direction). The width of the address bus determines how much memory can be addressed. A 32-bit address bus can address $2^{32}$ = 4 GB of memory.
Data bus: Carries data between the CPU and memory (two directions). The width determines how much data can be transferred per cycle. A 64-bit data bus transfers 8 bytes at once.
Control bus: Carries control signals from the CPU to other components (one direction). Signals include read/write, clock, and interrupt.

Worked Example. A CPU has a 16-bit address bus. What is the maximum addressable memory?

$2^{16} = 65536$ bytes = 64 KB.

Worked Example. A 32-bit data bus transfers 4 bytes per clock cycle. If the CPU runs at 2 GHz, What is the maximum data transfer rate?

$2 \times 10^9$ cycles/second $\times$ 4 bytes/cycle = $8 \times 10^9$ bytes/second = 8 GB/s.

2. Memory

2.1 Types of Memory

Type	Volatile?	Speed	Capacity	Purpose
RAM	Yes	Fast	Moderate	Stores currently running programs and data
ROM	No	Fast	Small	Stores the BIOS/start-up instructions
Cache	Yes	Very fast	Very small	Stores frequently used instructions and data
Secondary storage	No	Slow	Large	Long-term storage of files and programs

2.2 RAM vs ROM

Feature	RAM	ROM
Volatile	Yes (loses data when power is off)	No (retains data when power is off)
Read/Write	Both	Read only
Contents	Programs and data currently in use	Boot-up instructions (BIOS)
Can be changed	Yes	No (in traditional ROM)

RAM (Random Access Memory): When you open a program, it is loaded from secondary storage into RAM because RAM is much faster. When you save your work, it is copied from RAM to secondary storage So it persists after power off.

ROM (Read Only Memory): ROM contains the BIOS (Basic Input/Output System), which is the first Code the CPU executes when the computer is powered on. The BIOS initialises hardware and loads the Operating system from disk into RAM. ROM is non-volatile so the computer can always start up.

Dynamic RAM (DRAM) vs Static RAM (SRAM):

DRAM: Used for main memory. Stores each bit as a charge in a capacitor. Must be refreshed thousands of times per second. Cheaper, higher density.
SRAM: Used for CPU cache. Stores each bit in a flip-flop (transistor circuit). No refreshing needed. Faster but more expensive and lower density.

DRAM vs SRAM comparison:

Feature	DRAM	SRAM
Used for	Main memory (RAM)	CPU cache (L1/L2/L3)
Speed	Slower	Faster
Cost	Cheaper per bit	More expensive
Density	Higher	Lower
Refresh	Required	Not required
Power	Less (when idle)	More

2.3 Virtual Memory

When RAM is full, the operating system uses a section of the hard drive as additional RAM (called a swap file or page file). This is virtual memory.

Advantage: Allows the computer to run more programs than the physical RAM can hold.

Disadvantage: Much slower than physical RAM because hard drives are slower than RAM. A process That relies heavily on virtual memory will run noticeably slower.

Page fault: Occurs when the CPU tries to access data that has been moved from RAM to virtual Memory (the hard drive). The OS must swap the required page back into RAM, which takes thousands of Times longer than a RAM access.

Worked Example. A computer has 8 GB of RAM and runs programs that require 12 GB total. The Operating system allocates 8 GB to RAM and uses 4 GB of virtual memory on the SSD. When a program Accesses data in virtual memory, a page fault occurs and the OS swaps the required page from the SSD Into RAM, potentially moving a less-used page from RAM to the SSD.

Thrashing. If too many programs are running and the system spends more time swapping pages than Executing instructions, the system becomes extremely slow. This condition is called thrashing. The Solution is to close some programs or add more physical RAM.

2.4 Cache Memory

Cache memory is a small, very fast memory between the CPU and RAM. It stores the most frequently Used instructions and data so the CPU does not have to wait for slower RAM access.

Three levels of cache:

Level	Location	Size	Speed
L1	Inside CPU core	Smallest (few KB)	Fastest
L2	Inside CPU	Larger (256 KB - 1 MB)	Fast
L3	Shared across cores	Largest (up to 64 MB)	Slower than L1/L2

Cache hit: Data is found in the cache (fast access).

Cache miss: Data is not in the cache; must be fetched from RAM (slower).

Why caching works: Programs tend to access the same data repeatedly (temporal locality) and Access data near recently accessed data (spatial locality). Caching exploits these patterns to Dramatically reduce average memory access time.

Worked Example. If a CPU has a 90% cache hit rate, L1 cache access time is 1 ns, and RAM access Time is 100 ns, what is the average memory access time?

Average access time = $0.9 \times 1 + 0.1 \times 100 = 0.9 + 10 = 10.9$ ns.

Without cache, all accesses would take 100 ns. The cache provides a speedup of approximately $100 / 10.9 \approx 9.2\times$ .

3. Storage

3.1 Primary vs Secondary Storage

Feature	Primary Storage (RAM/ROM)	Secondary Storage
Volatile?	RAM yes, ROM no	No
Speed	Very fast	Slower
Capacity	Limited	Large
Connection	Directly accessed by CPU	Accessed via data bus
Examples	RAM, ROM, cache	HDD, SSD, USB, optical disc

3.2 Magnetic Storage (Hard Disk Drive)

Uses spinning magnetic platters and read/write heads
Large capacity, relatively cheap
Slower than SSD
Moving parts (can be damaged by physical shock)
Typical capacity: 500 GB to 20 TB

3.3 Solid State Storage

Uses flash memory (no moving parts)
Faster than HDD
More durable (no moving parts)
More expensive per GB
Examples: SSD, USB flash drives, SD cards
Typical capacity: 128 GB to 4 TB

3.4 Optical Storage

Uses lasers to read/write data
CD: 700 MB, DVD: 4.7 GB, Blu-ray: 25 GB
Slower than magnetic and solid state
Examples: CD-ROM, DVD-RW, Blu-ray

3.5 Comparing Storage Devices

Device	Speed	Capacity	Durability	Cost
HDD	Medium	Very high	Medium	Low
SSD	Fast	High	High	Medium
USB flash	Medium	Low-Medium	High	Low
Optical	Slow	Low-Medium	Low	Very low
Cloud	Varies	Varies	Varies	Subscription

Choosing storage: practical considerations:

A photographer storing thousands of RAW images needs high capacity (HDD or cloud).
A video editor needs fast read/write speeds (SSD).
A student backing up coursework needs portability (USB flash drive).
A business sharing files across offices needs cloud storage with collaboration features.

3.6 Cloud Storage (Higher Tier)

Data stored on remote servers accessed via the Internet.

Advantages:

Accessible from any device with an Internet connection
Automatic backups
Scalable (pay for what you use)
Collaboration (multiple users can access shared files)

Disadvantages:

Requires Internet connection
Ongoing subscription costs
Privacy and security concerns (data stored on third-party servers)
Dependent on the service provider’s uptime

4. Operating Systems

4.1 Functions of an Operating System

Function	Description
Memory management	Allocates RAM to programs, manages virtual memory
Processor management	Schedules CPU time for running programs
Device management	Controls hardware devices via drivers
File management	Organises files in directories, handles read/write operations
User interface	Provides a way for users to interact with the computer (GUI or CLI)
Security	Manages user accounts, permissions, and access control

Memory management in detail. The OS keeps track of which parts of RAM are in use and by which Program. When a program is launched, the OS allocates a block of RAM. When the program closes, the OS frees that memory. The OS also handles virtual memory by swapping pages between RAM and disk.

Processor scheduling. When multiple programs are running, the OS allocates CPU time to each Program using a scheduling algorithm (round-robin, priority-based, etc.). This gives the illusion of Multitasking even on a single-core CPU.

Common scheduling algorithms:

Algorithm	Description	Fairness
Round-robin	Each process gets a fixed time slice in turn	High
Priority-based	Higher-priority processes get CPU time first	Low
First-come, first-served	Processes served in order of arrival	Medium
Shortest job first	The process with the shortest expected time runs first	Medium

4.2 Types of User Interface

Graphical User Interface (GUI):

Uses windows, icons, menus, and pointers
User-friendly, easy to learn
Examples: Windows, macOS, Android
Best for: everyday users, visual tasks

Command Line Interface (CLI):

Text-based commands typed by the user
Requires knowledge of commands
Faster for experienced users, uses fewer resources
Examples: Windows Command Prompt, Linux terminal
Best for: system administration, scripting, automation

GUI vs CLI comparison:

Feature	GUI	CLI
Ease of use	Easy for beginners	Steep learning curve
Speed	Slower (mouse-driven)	Faster (keyboard-driven)
Resources	Higher (graphics)	Lower
Automation	Limited	Easy with scripting
Flexibility	Menu-driven	Full control

4.3 Utility Software

Utility software helps maintain and manage the computer:

Utility	Purpose
Disk defragmenter	Reorganises data on a HDD for faster access
Disk cleaner	Removes unnecessary files to free up space
Antivirus	Detects and removes malware
Compression software	Compresses and decompresses files
Backup software	Creates copies of data for recovery

Disk defragmentation. On a HDD, files can become fragmented — stored in non-contiguous clusters Across the disk. This slows down reading because the read head must move to multiple locations. Defragmentation reorganises files into contiguous blocks. Note: SSDs do not need defragmentation and It can actually reduce their lifespan.

4.4 Types of Operating System (Higher Tier)

Type	Description	Examples
Desktop	For personal computers	Windows, macOS, Linux
Mobile	For smartphones and tablets	iOS, Android
Real-time	Guarantees response within a fixed time	VxWorks, FreeRTOS
Embedded	Built into devices for specific functions	Car ECU, smart TV
Network	Manages network resources and services	Windows Server, Linux
Distributed	Multiple computers work together as one system	Cloud platforms

5. Embedded Systems

An embedded system is a computer system built into a larger device, designed to perform a Specific function.

Examples:

Washing machines (control programs for wash cycles)
Microwaves (timer and power settings)
Cars (engine management, ABS, airbags)
Traffic lights
Medical devices (pacemakers)
Smart thermostats

Characteristics of embedded systems:

Purpose-built for a single task
Often use ROM to store the program (does not change)
Limited processing power
May have no user interface or a simple one
Reliable and designed to run continuously
Operate in real-time (must respond within strict time constraints)

Embedded systems vs general-purpose computers:

Feature	Embedded System	General-Purpose Computer
Purpose	Single, specific task	Multiple tasks
Software	Fixed (in ROM/flash)	Changeable (install apps)
User interface	Minimal or none	Full GUI
Processing power	Limited	High
Real-time requirements	Often required	Not required

Worked Example. A traffic light controller is an embedded system. It runs a fixed program stored In ROM that cycles through red, amber, and green at set intervals. It has no screen or keyboard — Its only output is the lights themselves. It must respond within strict time limits (real-time) for Safety.

1.6 Embedded Systems

An embedded system is a computer system built into a larger device, designed to perform a Specific function.

Examples:

Washing machines (control programs for wash cycles)
Microwaves (timer and power settings)
Cars (engine management, ABS, airbags)
Traffic lights
Medical devices (pacemakers)
Smart thermostats

Characteristics of embedded systems:

Purpose-built for a single task
Often use ROM to store the program (does not change)
Limited processing power
May have no user interface or a simple one
Reliable and designed to run continuously
Operate in real-time (must respond within strict time constraints)

1.7 Instruction Set and Machine Code (Higher Tier)

Machine code: Binary instructions that the CPU can execute directly.

Assembly language: Human-readable representation of machine code using mnemonics (e.g., ADD, SUB, MOV, JMP).

Example machine code instructions:

Instruction	Meaning
0000 0001	Load accumulator from address
0000 0010	Store accumulator to address
0000 0011	Add value to accumulator
0000 0100	Subtract value from accumulator
0000 0101	Jump to address
0000 0110	Jump to address if accumulator=0
0000 0111	Halt

Worked Example. Write the machine code to add two numbers stored at addresses 10 and 11 and Store the result at address 12.

LOAD from address 10: 0000 0001 0000 1010
ADD from address 11: 0000 0011 0000 1011
STORE to address 12: 0000 0010 0000 1100
HALT: 0000 0111

1.8 Pipelining (Higher Tier)

Pipelining overlaps the fetch, decode, and execute stages so that multiple instructions are Processed simultaneously. While one instruction is being executed, the next is being decoded, and the One after that is being fetched.

Analogy. Like a factory assembly line: while one car is being painted, the next is being Assembled, and the next is having its frame built.

Benefits: Increases instruction throughput. A 3-stage pipeline can theoretically complete one Instruction per clock cycle (vs one every 3 cycles without pipelining).

Problems:

Branch hazards: When a conditional branch is encountered, the pipeline does not know which instruction to fetch next. Branch prediction guesses the outcome to keep the pipeline full.
Data hazards: An instruction depends on the result of a previous instruction that has not yet completed.

2. Memory

2.1 Types of Memory

Type	Volatile?	Speed	Capacity	Purpose
RAM	Yes	Fast	Moderate	Stores currently running programs and data
ROM	No	Fast	Small	Stores the BIOS/start-up instructions
Cache	Yes	Very fast	Very small	Stores frequently used instructions and data
Secondary storage	No	Slow	Large	Long-term storage of files and programs

2.2 RAM vs ROM

Feature	RAM	ROM
Volatile	Yes (loses data when power is off)	No (retains data when power is off)
Read/Write	Both	Read only
Contents	Programs and data currently in use	Boot-up instructions (BIOS)
Can be changed	Yes	No (in traditional ROM)

Dynamic RAM (DRAM) vs Static RAM (SRAM):

DRAM: Used for main memory. Stores each bit as a charge in a capacitor. Must be refreshed thousands of times per second. Cheaper, higher density.
SRAM: Used for CPU cache. Stores each bit in a flip-flop (transistor circuit). No refreshing needed. Faster but more expensive and lower density.

2.3 Virtual Memory

When RAM is full, the operating system uses a section of the hard drive as additional RAM (called a swap file or page file). This is virtual memory.

Advantage: Allows the computer to run more programs than the physical RAM can hold.

Disadvantage: Much slower than physical RAM because hard drives are slower than RAM.

2.4 Flash Memory

Flash memory is a type of non-volatile storage used in SSDs, USB drives, and SD cards. It stores Data in floating-gate transistors and can be electronically erased and rewritten.

Advantages over HDD: Faster, no moving parts, more durable, lower power consumption.

Limitation: Each cell has a finite number of write cycles before it becomes unreliable (though This is tens of thousands of cycles, far exceeding normal use).

5. Embedded Systems

An embedded system is a computer system built into a larger device, designed to perform a Specific function.

Examples:

Washing machines (control programs for wash cycles)
Microwaves (timer and power settings)
Cars (engine management, ABS, airbags)
Traffic lights
Medical devices (pacemakers)
Smart thermostats

Characteristics of embedded systems:

Purpose-built for a single task
Often use ROM to store the program (does not change)
Limited processing power
May have no user interface or a simple one
Reliable and designed to run continuously
Operate in real-time (must respond within strict time constraints)

Embedded systems vs general-purpose computers:

Feature	Embedded System	General-Purpose Computer
Purpose	Single, specific task	Multiple tasks
Software	Fixed (in ROM/flash)	Changeable (install apps)
User interface	Minimal or none	Full GUI
Processing power	Limited	High
Real-time requirements	Often required	Not required

6. The Systems Life Cycle

6.1 Stages

Analysis: Understanding the problem; identifying requirements; consulting stakeholders
Design: Planning the solution; designing data structures, user interface, and program structure
Implementation: Writing the code; creating the database; building the system
Testing: Checking that the system works correctly and meets the requirements
Evaluation: Reviewing the system against the original requirements; identifying improvements
Maintenance: Fixing bugs and making improvements after deployment

Why follow a life cycle? A structured approach reduces the risk of building the wrong system, Exceeding the budget, or delivering late. Each stage produces documentation that guides the next Stage and provides a record for future maintenance.

6.2 Types of Testing

Type	Description
Unit testing	Testing individual components in isolation
Integration testing	Testing that components work together correctly
System testing	Testing the entire system as a whole
Acceptance testing	Customer tests the system to ensure it meets requirements
Alpha testing	Testing by the development team
Beta testing	Testing by a group of real users

Black-box vs white-box testing:

Black-box: Testing based on inputs and expected outputs without knowledge of internal code. Focuses on what the system does.
White-box: Testing based on knowledge of the internal structure. Focuses on how the system works.

Boundary value analysis. Most bugs occur at boundaries. If a function accepts ages 0-120, test -1, 0, 1, 119, 120, 121 rather than random values in the middle of the range.

Worked Example. A function validates that a percentage is between 0 and 100 inclusive. Using Boundary value analysis, the test cases should include: -1, 0, 1, 99, 100, 101. The values 0 and 100 Are the boundaries where off-by-one errors are most likely.

Worked Example (Higher Tier). For a search function that accepts a string of 1 to 50 characters, Identify the equivalence classes and boundary values.

Equivalence classes: valid (1-50 characters), too short (0 characters), too long (51+ characters).

Boundary values: 0, 1, 2, 49, 50, 51 characters.

Common Pitfalls

Confusing RAM and ROM. RAM is volatile and holds current data; ROM is non-volatile and holds boot instructions. RAM is read-write; ROM is read-only (in traditional implementations).
Getting the fetch-decode-execute cycle wrong. Remember the order: fetch from memory (PC to MAR, memory to MDR, increment PC, MDR to CIR), decode the instruction (CU interprets CIR), execute (ALU calculates, data moves).
Confusing registers. PC holds the address of the NEXT instruction; MAR holds the address being accessed; MDR holds the DATA. If you confuse address and data, you will get the cycle wrong.
Thinking SSDs have no limit on read/write cycles. SSDs do have a limit (though much higher than expected lifespan for most users). Each flash memory cell can only be written a finite number of times before it becomes unreliable.
Confusing embedded systems with general-purpose computers. Embedded systems are designed for a single specific task and run fixed software stored in ROM.
Forgetting that virtual memory is on the hard drive, which is much slower than physical RAM. Heavy reliance on virtual memory causes significant performance degradation.
Confusing the address bus and data bus. The address bus carries addresses (one direction: CPU to memory). The data bus carries data (two directions: CPU to/from memory).
Confusing DRAM and SRAM. DRAM is used for main memory and needs refreshing. SRAM is used for cache and does not need refreshing. SRAM is faster but more expensive.

Practice Questions

Describe the function of each of the following CPU components: ALU, CU, cache, and registers.
Explain the fetch-decode-execute cycle, including the role of the Program Counter, MAR, and MDR.
Compare RAM and ROM in terms of volatility, purpose, and whether they can be read and written to.
Compare three different types of secondary storage, explaining the advantages and disadvantages of each.
Explain four functions of an operating system.
Describe the difference between a GUI and a CLI, giving advantages and disadvantages of each.
Explain what an embedded system is and give three examples.
Describe the stages of the systems life cycle.
Explain why cache memory improves the performance of a computer.
Explain the difference between HDD and SSD storage, including why SSDs are generally faster.
(Higher Tier) Explain the purpose of each of the three buses (address bus, data bus, control bus) and what they carry.
(Higher Tier) Explain what virtual memory is, why it is needed, and why it is slower than physical RAM.
(Higher Tier) Describe three differences between DRAM and SRAM.
(Higher Tier) A computer has a 32-bit address bus. What is the maximum amount of memory it can address?
(Higher Tier) A CPU has a cache hit rate of 85%. L1 cache access takes 2 ns and RAM access takes 80 ns. Calculate the average memory access time.
(Higher Tier) Explain the Von Neumann bottleneck and describe two techniques used by modern CPUs to overcome it.
(Higher Tier) Explain the difference between round-robin and priority-based scheduling. Give an advantage and disadvantage of each.
(Higher Tier) A 64-bit data bus transfers 8 bytes per clock cycle. If the CPU clock speed is 3.5 GHz, calculate the maximum data transfer rate in GB/s.
(Higher Tier) Explain what is meant by pipelining. How does it improve CPU performance, and what is a branch hazard?
(Higher Tier) Explain the difference between DRAM and SRAM. Why is each used in its respective role?
(Higher Tier) Explain what flash memory is and why it is used in SSDs instead of magnetic storage.
(Higher Tier) A CPU has a 16-bit address bus and a 32-bit data bus running at 2.5 GHz. Calculate the maximum addressable memory and the maximum data transfer rate.
Explain the role of the BIOS/UEFI when a computer is powered on. What would happen if the ROM containing the BIOS were corrupted?
A computer has 4 GB of RAM. Explain what happens when programs require 6 GB total. Include the terms “virtual memory”, “page fault”, and “thrashing” in your answer.

Worked Examples

Example 1:

A typical exam question on Computer Systems requires you to apply your knowledge to an unfamiliar context. Read the question carefully, identify the key concept being tested, and structure your answer using the appropriate terminology.

Example 2:

Multi-step problems in Computer Systems often combine two or more concepts. Break the problem down: identify what you need to find, recall the relevant formula or principle, substitute values, and state your answer with correct units or formatting.

Summary

This topic covers the core concepts of computer systems, including underlying theory, practical implementation, and key applications.

Key concepts include:

CPU architecture and the fetch-decode-execute cycle
memory hierarchy (cache, RAM, virtual)
input/output systems
operating systems and scheduling
interrupts and polling

Understanding these concepts thoroughly is essential for both examinations and practical programming, and requires both theoretical knowledge and hands-on practice.

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