🔑 Key Language and Definitions for OCR A Level Computer Science Paper 1
1. CPU Architecture
• ALU – Performs arithmetic and logic operations.
• CU (Control Unit) – Manages execution of instructions.
• Registers (PC, MAR, MDR, ACC) – Fast storage used during the FDE cycle.
• Von Neumann Architecture – Shared memory for data and instructions.
• Fetch-Decode-Execute Cycle – Steps the CPU follows to run a program.
• Buses – Data bus (transfers data), address bus (transfers memory
locations), control bus (manages control signals).
• Clock Speed – Determines how many instructions per second are
processed.
• Pipelining – Overlapping fetch, decode, and execute steps to improve
CPU efficiency.
2. Types of Processor
• CISC (Complex Instruction Set Computer) – Many instructions, complex
hardware.
• RISC (Reduced Instruction Set Computer) – Fewer, simpler instructions,
faster execution.
• Parallel Processing – Multiple processors work on tasks simultaneously.
• GPU – Optimised for tasks with large numbers of parallel calculations
(e.g. graphics).
• Harvard Architecture – Separate memory for instructions and data.
3. Input/Output/Storage Devices
• Solid-State Storage (SSD) – No moving parts, fast, durable.
• Magnetic (HDD) – Large capacity, mechanical.
• Optical (CD/DVD) – Uses lasers to read/write.
• Volatile Memory – Loses data when power is off (RAM).
• Non-Volatile Memory – Retains data without power (ROM).
• Random Access vs Sequential Access – RAM is random; tape is sequential.
4. Software Types
• System Software – Includes OS, utilities, drivers.
• Application Software – Word processors, games, browsers.
• Utility Software – Disk defragmenters, antivirus, compression.
• Open Source – Code can be viewed/edited; free license.
• Proprietary – Owned by a company; source code hidden.
• Compiler – Translates all code at once into machine code.
• Interpreter – Translates line-by-line; useful for debugging.
5. Operating Systems
• Memory Management – Allocates memory to processes.
• Scheduling – Controls execution order (e.g. Round Robin, SJF).
• Interrupts – Signals that stop current tasks for urgent ones.
• Context Switching – Saving and loading process states.
• Virtual Memory – Uses secondary storage as additional RAM.
6. Programming Concepts
• Variable – Stores data that can change.
• Constant – Value cannot be changed once set.
• Iteration – Repeating tasks (e.g. for, while).
• Selection – Decision-making (if, else).
• Recursion – Function calling itself.
• Function vs Procedure – Function returns a value, procedure does not.
• Scope – Local (inside function) or global (whole program).
7. Programming Paradigms
1. CPU Architecture
• ALU – Performs arithmetic and logic operations.
• CU (Control Unit) – Manages execution of instructions.
• Registers (PC, MAR, MDR, ACC) – Fast storage used during the FDE cycle.
• Von Neumann Architecture – Shared memory for data and instructions.
• Fetch-Decode-Execute Cycle – Steps the CPU follows to run a program.
• Buses – Data bus (transfers data), address bus (transfers memory
locations), control bus (manages control signals).
• Clock Speed – Determines how many instructions per second are
processed.
• Pipelining – Overlapping fetch, decode, and execute steps to improve
CPU efficiency.
2. Types of Processor
• CISC (Complex Instruction Set Computer) – Many instructions, complex
hardware.
• RISC (Reduced Instruction Set Computer) – Fewer, simpler instructions,
faster execution.
• Parallel Processing – Multiple processors work on tasks simultaneously.
• GPU – Optimised for tasks with large numbers of parallel calculations
(e.g. graphics).
• Harvard Architecture – Separate memory for instructions and data.
3. Input/Output/Storage Devices
• Solid-State Storage (SSD) – No moving parts, fast, durable.
• Magnetic (HDD) – Large capacity, mechanical.
• Optical (CD/DVD) – Uses lasers to read/write.
• Volatile Memory – Loses data when power is off (RAM).
• Non-Volatile Memory – Retains data without power (ROM).
• Random Access vs Sequential Access – RAM is random; tape is sequential.
4. Software Types
• System Software – Includes OS, utilities, drivers.
• Application Software – Word processors, games, browsers.
• Utility Software – Disk defragmenters, antivirus, compression.
• Open Source – Code can be viewed/edited; free license.
• Proprietary – Owned by a company; source code hidden.
• Compiler – Translates all code at once into machine code.
• Interpreter – Translates line-by-line; useful for debugging.
5. Operating Systems
• Memory Management – Allocates memory to processes.
• Scheduling – Controls execution order (e.g. Round Robin, SJF).
• Interrupts – Signals that stop current tasks for urgent ones.
• Context Switching – Saving and loading process states.
• Virtual Memory – Uses secondary storage as additional RAM.
6. Programming Concepts
• Variable – Stores data that can change.
• Constant – Value cannot be changed once set.
• Iteration – Repeating tasks (e.g. for, while).
• Selection – Decision-making (if, else).
• Recursion – Function calling itself.
• Function vs Procedure – Function returns a value, procedure does not.
• Scope – Local (inside function) or global (whole program).
7. Programming Paradigms
