CS PAPER1

Control Unit (CU)

Sends control signals, executes programs via the fetch-decode-execute cycle, contains the clock, and the decoder.

Arithmetic Logic Unit (ALU)

Carries out calculations (add, subtract, multiply, divide) and logical operations (>,

Program Counter (PC)

Holds the memory address of the next instruction.

Memory Address Register (MAR)

Stores the address of data fetched from or sent to memory.

Memory Data Register (MDR)

Stores the data fetched from or about to be stored in memory.

Current Instruction Register (CIR)

Stores the most recently fetched instruction.

Accumulator (ACC)

Holds results of calculations/operations from the ALU.

Address Bus

Provides memory addresses to system memory or I/O devices.

Data Bus

Transfers data between the CPU and memory or I/O devices.

Control Bus

Provides control signals for memory or I/O operations (read/write).

Fetch-Decode-Execute Cycle

A process where the CPU fetches an instruction, decodes it, and executes it.

Clock Speed

Higher clock speed means more instructions can be completed per second.

Cache

Small, fast memory within the CPU that stores frequently or recently used data/instructions.

Number of Cores

Each core is a complete processing unit with its own CU, ALU, registers, etc.

Pipelining

A technique where the CPU fetches one instruction while decoding the prior and executing the one before that.

Von Neumann Architecture

Single CU and ALU. Instructions and data stored together in the same memory.

Harvard Architecture

Separate memory for data and programs, each with a different bus.

Contemporary Architecture

Uses parallel processing, including pipelining, array processing (SIMD), and multicore processing (MIMD).

CISC (Complex Instruction Set Computing)

Supports more instructions, requires more transistors, larger, more power, more heat.

RISC (Reduced Instruction Set Computing)

Supports fewer instructions, requires less transistors, smaller, less power, less heat.

GPU (Graphics Processing Unit)

Specifically designed for graphics calculations.

Applications of GPUs

Gaming, animation, computer-aided design, modelling physical systems, audio processing, cryptography, machine learning, and more.

Parallel Processing

Simultaneous processing of data.

SIMD (Single Instruction, Multiple Data)

Same operation on multiple data sets.

MIMD

Different instructions on different data sets, often using multiple cores or CPUs. Can be achieved by having multiple cores inside a CPU or across workstations, supercomputers, and distributed systems.

Input Devices

Keyboard, mouse, microphone, scanner, joystick.

Output Devices

Printer, speakers, monitors, actuators.

Storage Devices

Used to hold data and programs long-term and are non-volatile.

Categories of storage

Magnetic, Flash, and Optical.

Magnetic Storage

Hard disk drives, magnetic tape. High capacity, low cost but vulnerable to magnetic fields and shock.

Optical Storage

CDs, DVDs, Blu-rays. Cheap to produce, fairly reliable if not scratched.

Flash Memory

Memory sticks, memory cards, SSDs. High speed, low power, but more expensive per gigabyte.

RAM

Primary memory for temporarily storing programs and data being run by the computer.

ROM

Primary memory that is non-volatile and stores instructions to boot the computer (BIOS). Can contain the firmware for an embedded system.

Virtual Storage

Data stored over the internet rather than locally.

Advantages of Virtual Storage

Access from anywhere, easy data sharing, scalability, backup and security handled by a third party.

Disadvantages of Virtual Storage

Requires fast internet, can be expensive for large amounts of data, requires trusting the service provider.

Operating System (OS)

An OS manages computer hardware and software.

Purposes of an OS

Manages hardware/peripherals, provides a user interface, provides a platform to run software, manages system security, manages CPU usage through scheduling and interrupts, provides utilities for system maintenance, manages available memory.

Memory Management

The memory manager controls RAM allocation for running processes.

Virtual Memory

Manages virtual memory to load/run programs even if physical RAM is full.

Interrupts

Signals from hardware or software that need the CPU's immediate attention.

Process of handling Interrupts

1. The CPU checks for interrupts at the end of each fetch-decode-execute cycle. 2. If an interrupt of higher priority occurs the program counter and other registers are copied to the stack. 3. The interrupt service routine (ISR) is loaded. 4. After the ISR is complete the program counter and registers are restored and normal program execution resumes.

CPU Scheduling

The OS uses algorithms to share processor time between multiple running applications.

CPU Scheduling Algorithms

Round Robin, First Come First Served, Shortest Job First, Shortest Remaining Time, Multi-level Feedback Queues.

Types of Operating Systems

Multitasking OS, Multi-user OS, Distributed OS, Embedded OS, Real-time OS.

Device Drivers

Software that allows the OS to understand data from external devices.

BIOS

Controls the startup sequence and configures hardware.

Virtual Machine (VM)

A program that simulates a computer in software.

Uses of Virtual Machines

Run multiple operating systems on the same computer, split a powerful server into smaller VMs, and improve security.

Application Software

Software that allows a user to perform a task or produce something (e.g., word processor, spreadsheet).

Utilities

Small programs for system maintenance (e.g., disk cleanup, defragmenter, compression, encryption).

Open Source Software

Source code is available, often free, can be modified by users. Encourages collaboration.

Closed Source Software

Source code is proprietary, usually more polished and user-friendly, often with warranty/support.

Assembler

Converts assembly code into machine code.

Interpreter

Converts high-level code line by line, good for debugging.

Compiler

Converts high-level code into machine code all at once, faster execution.

Lexical Analysis

Removes comments and whitespace, creates tokens, builds a symbol table.

Syntax Analysis

Produces an abstract syntax tree to represent the program, checks for correct syntax.

Code Generation and Optimization

Converts the syntax tree into object code. Compilers are tweaked to optimize for either speed or memory.

Linkers

Incorporate library code into the final program.

Loaders

Responsible for loading the executable file into memory.

Waterfall

Sequential stages, linear. Good for clear outputs and stable requirements but inflexible.

Rapid Application Development (RAD)

Builds a prototype, iteratively refined. Good for unclear requirements but doesn't scale well.

Spiral Model

Manages risk at each stage, good for large, risky projects. Requires expertise in risk analysis.

Agile

Deals with changing requirements. Includes Extreme Programming (XP) which focuses on high-quality code.

Algorithmic Thinking

A process for solving problems using a set of instructions (an algorithm). Can be represented using pseudocode or flowcharts.

Low-Level Languages

Machine code and Assembly language, close control of CPU, very efficient.

High-Level Languages

Closer to human language.

Imperative Programming

Tells the computer what to do step by step.

Procedural Programming

Instructions in sequence, broken into procedures/functions (e.g., Basic, C, Pascal).

Object-Oriented Programming

Uses interacting objects (e.g., Java, C++, C#).

Declarative Programming

Tells the computer the qualities of the solution not how to compute it.

Logic Programming

For AI applications (e.g., Prolog).

Functional Programming

For calculations and simulations (e.g., Lisp, Wolfram).

Assembly Language

Uses mnemonics to represent machine code instructions.

Little Man Computer (LMC)

A simplified version used for learning purposes.

Simple LMC Program

1. INP: Input a number and store it in the accumulator. 2. STA num: Store the accumulator value in memory location num. 3. INP: Input a second number, overwrites accumulator value. 4. ADD num: Add the value in memory location num to the accumulator. 5. OUT: Output the value in the accumulator. 6. HLT: Halt the program. 7. num DAT: Declare a memory location labelled num.

LMC program

A program that compares two numbers using a series of instructions including input, storage, subtraction, and output.

Immediate Addressing

The data to be used is hardcoded into the instruction.

Direct Addressing

The operand contains the memory address.

Indirect Addressing

The operand contains the memory address where the data address is stored.

Indexed Addressing

The final address is calculated by adding an offset to a base address.

Object-Oriented Programming (OOP)

Organizes programs around data/objects rather than functions/logic.

Class

A template for creating objects (defines attributes and methods).

Object

An instance of a class with specific attributes and behaviors.

Attributes

Data fields that describe an object.

Methods

Procedures and functions to act on the object's data.

Abstraction

Hides internal mechanisms, revealing only relevant details.

Encapsulation

Data and methods are bundled within the object. Data is made private and not accessible from outside of the class to provide program security.

Inheritance

Class inherits attributes and methods from a parent class.

Polymorphism

Use the same code to process different objects based on their type.

Compression

Reduces file size.

Lossy Compression

Removes data to reduce file size, irreversible, reduces quality (e.g. images, videos).

Lossless Compression

No data is lost, reversible, maintains original quality.

Run Length Encoding (RLE)

Replaces repeating sequences of data with a single data value and a count.

Dictionary Coding

Stores repeated data once in a dictionary with a pointer to its position.

Encryption

Scrambling data so only authorized users can read it.

Symmetric Encryption

Same key for encryption and decryption.

Asymmetric Encryption

Two different keys (public and private). Public key encrypts and private key decrypts. Better for internet use because the keys do not need to be exchanged.