iGCSE Computer Science CAIE

This subject is broken down into 20 topics in 2 modules:

  1. Theory of Computer Science 15 topics
  2. Practical Problem-Solving and Programming 5 topics
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This page was last modified on 28 September 2024.

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Computer Science

Theory of Computer Science

Binary Systems

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Binary Systems

Understanding Binary Systems

  • A Binary system is a number system that uses only two digits: 0 and 1.
  • The binary system is used inside electronic computers because binary digits can be easily represented by digital electronic circuits.
  • In the binary system, base is 2. This means that each digit in binary represents power of 2.
  • A binary digit is called a bit. It is the fundamental unit of data in a computer system.

Binary Conversion

  • Binary can be converted from/to decimal using mathematical computations.
  • Binary to decimal conversion involves multiplying each binary digit by 2 raised to their specific position from right (starting from 0) and summing up all values.
  • Decimal to binary involves dividing the number by 2 repeatedly until the quotient is 0. The binary value is the remainder reading from bottom up.

Binary Addition and Subtraction

  • Binary addition and subtraction follow the same basic principle as in the decimal system with '0' and '1' instead of '0' through '9'.
  • Addition: 0+0 = 0, 0+1 = 1, 1+0 = 1, 1+1 = 0 (with a carry 1).
  • Subtraction: 1-0 = 1, 0-1 =1 (with a borrow of 1), 1-1=0, 0-0=0.

Bitwise Operations

  • AND, OR, XOR and NOT are bitwise operations working on one or more bit patterns.
  • Using these operations, you can manipulate data at bit level.
  • A NOT operation flips the value of a bit, whereas AND, OR and XOR operations are performed on two bits at a time.

Representing Text and Images in Binary

  • Text can be represented using ASCII or Unicode, converting characters into binary digits.
  • Images are converted into binary using bitmap or vector graphics approaches. Bitmap represents images using pixels whereas vector uses points, lines and polygons.

Encoding Data

  • Data can be encoded using methods such as parity check and checksum for error detection.
  • In case of a single parity check, an additional bit is added to ensure the total number of 1-bits is even (even parity) or odd (odd parity).
  • Checksum is a more advanced method that involves adding all bits together and transmitting the sum along with data for error checking.

Course material for Computer Science, module Theory of Computer Science, topic Binary Systems

Computer Science

Theory of Computer Science

Memory, Storage Devices and Media

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Memory, Storage Devices and Media

Understanding Computer Memory and Storage

  • Computer memory is an electronic storage space where data is temporarily stored to be processed, while storage devices are peripherals where data is permanently saved.
  • Memory is volatile (data is lost when power is cut), while storage is non-volatile (data remains even without power).
  • Random Access Memory (RAM) is the main type of volatile memory, used to store data and instructions currently in use, and directly accessible by the CPU.
  • Read-Only Memory (ROM) is non-volatile and contains data that is permanently written during manufacturing (like BIOS).
  • Cache is a small amount of high-speed volatile memory used to store frequently accessed data for rapid access.

Different Types of Storage Devices

  • Hard Disk Drives (HDDs) are non-volatile, magnetic storage devices with high capacity but relatively slower speeds.
  • Solid State Drives (SSDs) are non-volatile storage devices that use flash memory, offering faster speeds than HDDs.
  • Optical storage devices like CDs, DVDs, and Blu-ray discs store data using light, offering large storage capacities but slower read/write speeds.
  • Removable storage devices like USBs and memory cards offer portability and compatibility with various devices.

Understanding Storage Media

  • Magnetic storage media like HDDs and tape drives use magnets to store data, offer high storage capacities but are prone to physical wear and damage.
  • Optical storage media like CDs and DVDs use lasers to burn pits into a reflective surface to store data, and are relatively safe from hacking.
  • Solid-state storage media like SSDs and USB flash drives use electronic circuits to store data, offer fast read/write speeds, and are durable and shock-resistant.

Storage Capacity and Speed

  • The capacity of storage devices is usually measured in bytes - kilobytes (KB), megabytes (MB), gigabytes (GB), terabytes (TB), and beyond.
  • The speed of storage devices affects how quickly data can be written to or read from the device.
  • SSDs are faster than HDDs because they have no moving parts and can access data electronically.

Impact on System Performance

  • The amount of RAM in a computer affects its ability to multitask and run demanding applications smoothly.
  • Having a fast storage device can significantly reduce load times and improve overall system responsiveness.

Data Retrieval and Storage

  • Data stored on a HDD is read by a moving read/write head, while data on an SSD is accessed electronically.
  • Optical drives use lasers to read and write data.
  • In the case of tape drives, data is read sequentially, which can be slower compared to random access devices such as hard drives.

Choosing the Right Storage Device

  • The choice of storage device depends on several factors, such as required storage capacity, speed, portability, durability, and cost.
  • For example, an SSD might be chosen for its speed and durability, while an HDD might be chosen for its larger storage capacity and lower cost.

Course material for Computer Science, module Theory of Computer Science, topic Memory, Storage Devices and Media

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