OCR AS Level Computer Science - 2024 Past Paper Notes

Chapter 1: Introduction

  • OCR AS level computer science H046/01 computing principles 2024 past paper.
  • Total mark: 70.

Question 1

  • Identify labeled components:
    • A: Data Bus
    • B: MAR (Memory Address Register)
    • C: Program Counter
    • D: MDR (Memory Data Register)
    • E: Accumulator (ACC)

Chapter 2: Harvard Architecture

Question 2

  • Discuss difference between Von Neumann and Harvard architecture:
    • Harvard Architecture:
      • Uses separate memory for data and instructions.
      • Uses separate data and address buses for each memory.
      • Can read and write data and instructions simultaneously.
    • Von Neumann Architecture:
      • Uses one physical memory for both data and instructions.
      • Uses one data and one address bus.
      • Can only read and write data OR instructions at a time, not simultaneously.
    • Comparison:
      • Von Neumann is less complex and cheaper.
      • Harvard is more complex, requires two buses, more CPU pins, and a complex motherboard.
      • Harvard: Free data memory cannot be used for instructions.
      • Harvard allows faster processing because instructions and data are fetched and executed simultaneously.
      • Harvard splits memory statically; Von Neumann allows dynamic allocation.
      • Von Neumann caters to large programs with small data or small programs with large data.

Chapter 3: Instructions Or Data

Question 3 (a) I

  • Advantage of using virtual machines for a secondary school upgrading computers:
    • Allows for more efficient use of computing resources as workstations are less likely to run idle.

Question 3 (a) II

  • Disadvantage of using virtual machines:
    • Can cause network overload if the network does not have sufficient bandwidth.

Question 3 (b)

  • Two other types of operating systems:
    • Multitasking: Optimized to do multiple processes simultaneously; can run multiple programs at the same time.
    • Embedded: Has a restricted set of operations and is read-only.

Question 3 (c) I

  • Difference between utility software and application software:
    • Application Software: Allows users to solve a problem and complete a task.
    • Utility Software: Designed to monitor, manage, and maintain a computer system.

Question 3 (c) II

  • Two different types of application software used by students:
    • Word Processor: Allows students to write essays.
    • Presentation Software: Allows students to create presentations about particular topics.

Chapter 4: Software And Application

Question 3 (c) III

  • Advantage to a school using open source software:
    • Allows access to the source code, which can be tailored to specific needs, potentially wider bug fixes, and a wider pool of support compared to proprietary software.

Question 3 (d)

  • Three different types of utility software:
    • Disk defragmentation software
    • Device driver software
    • Antivirus software

Question 4 (a)

  • Translator Types:
    • Create executable file: Compiler
    • Creates one line of object code for each line source code: Assembler
    • Translate all the high level code at once: Compiler
    • A program needs to be translated each time it's run: Interpreter

Chapter 5: Open Source Software

Question 4 (b)

  • Most suitable translator for a computer game:
    • Type: Compiler
    • Reason: Protects the original source code, preventing competitors from stealing ideas.

Question 4 (c)

  • Assembly language algorithm (Little Man Computer instruction set):
INP
STA numA
INP
STA numB
loopStart LDA numB
BRZ loopEnd
SUB one
STA numB
LDA answer
ADD numA
STA answer
BRA loops
loopEnd LDA answer
OUT
HLT
answer DAT 0
one DAT 1
numA DAT 0
numB DAT 0

Question 5

  • JavaScript code for password length check:
function errorCheck() {
  var pass = document.getElementById("password").value;
  if (pass.length > 12 || pass.length < 8) {
    document.getElementById("errorText").innerHTML = "Password length error";
  }
}

Chapter 6: Question C

Question 6 (a) I

  • Convert binary value 10011101 to a positive denary number:
    • 157

Question 6 (a) II

  • Convert binary value 10011101 to a negative denary number (two's complement):
    • -99

Question 6 (a) III

  • Convert binary value 10011101 to a hexadecimal value:
    • 9D

Chapter 7: The Binary Value

Question 6 (b)

  • Discuss different types of data stored in binary and why computers use binary:
    • Types of data: numeric, alphanumeric, sound, images, and video.
    • Binary stored text: Uses character sets like ASCII and extended ASCII; each character has a separate binary code; more bits per character increase the number of possible characters.
    • Numbers: Stored using binary; sign of magnitude and two's complement for negative numbers; floating-point binary for decimal points.
    • Images: Split into pixels, each with a binary value representing color.
    • Sound: Analog sound is sampled, and samples are stored as binary numbers.
    • Reasons computers use binary: Computers are made of switches or logic gates with two states (0 or 1, on or off), which easily translates to binary values.

Chapter 8: Binary Stored Text

Question 7 (a) I

  • Complete the truth table for the logic diagram:
    • 0, 1, 1, 0

Question 7 (a) II

  • Which single gate is equivalent to the logic gate diagram?
    • XOR

Question 7 (b)

  • Draw the logic gate diagram for the expression: Q = A \text{ OR } (\text{NOT } B \text{ AND } C)

Chapter 9: Separate Binary Code

Chapter 10: Conclusion