GCSE Computer Science Paper
1 (Topics 1–2)
1.1 Systems architecture
1.1.1 Architecture of the CPU
Hardware and software -
Hardware is the physical components of the computer
e.g. CPU, monitor, hard disk, mouse and keyboard
Software is the programs that run on the computer
e.g. macOS, Microsoft Defender, Linux, Windows 11 and Google Drive
Computer model -
Data is input, processed and either outputted or sent to secondary storage
Data is held in primary storage while it is being processed
The CPU receives instructions and data from an input or memory, Then the
instructions are processed by the processed by the CPU and the results are
either outputted or sent to secondary storage
💡 The CPU performs the fetch-execute cycle (which processes data or
instructions) and controls the computer system
Fetch-Decode-Execute Cycle -
Fetch
Memory address copied from the PC to the MAR
Increment (increase) the PC to the address of the next instruction, ready
for the next instruction
Instruction copied from MAR to the MDR
GCSE Computer Science Paper 1 (Topics 1–2) 1
, Decode
Instruction from the MDR is decoded by the CU
CU loads value to the MAR or the MDR
Execute
Instruction is performed
CPU components -
There are six main components:
Control Unit (CU)
Manages instructions using the decoder
Fetch, Decode, Execute (FDE)
Controls signals
Moves data using the clock
Arithmetic Logic Unit (ALU)
Performs arithmetic and logical operations (decisions)
Acts as a gateway between primary memory and secondary storage
Registers
High-speed memory in the CPU
Program Counter (PC) - memory location address of instruction for
the next cycle performed by the CPU
Memory Address Register (MAR) - memory address of data to be
retrieved or stored or instruction to be executed
Memory Data Register (MDR) - holds data or instruction fetched
from memory or is about to be stored in memory
Current Instruction Register (CIR) - holds instruction currently being
decoded and executed
Accumulator (ACC) - stores intermediate results of the calculations
performed by the ALU
Cache
GCSE Computer Science Paper 1 (Topics 1–2) 2
1 (Topics 1–2)
1.1 Systems architecture
1.1.1 Architecture of the CPU
Hardware and software -
Hardware is the physical components of the computer
e.g. CPU, monitor, hard disk, mouse and keyboard
Software is the programs that run on the computer
e.g. macOS, Microsoft Defender, Linux, Windows 11 and Google Drive
Computer model -
Data is input, processed and either outputted or sent to secondary storage
Data is held in primary storage while it is being processed
The CPU receives instructions and data from an input or memory, Then the
instructions are processed by the processed by the CPU and the results are
either outputted or sent to secondary storage
💡 The CPU performs the fetch-execute cycle (which processes data or
instructions) and controls the computer system
Fetch-Decode-Execute Cycle -
Fetch
Memory address copied from the PC to the MAR
Increment (increase) the PC to the address of the next instruction, ready
for the next instruction
Instruction copied from MAR to the MDR
GCSE Computer Science Paper 1 (Topics 1–2) 1
, Decode
Instruction from the MDR is decoded by the CU
CU loads value to the MAR or the MDR
Execute
Instruction is performed
CPU components -
There are six main components:
Control Unit (CU)
Manages instructions using the decoder
Fetch, Decode, Execute (FDE)
Controls signals
Moves data using the clock
Arithmetic Logic Unit (ALU)
Performs arithmetic and logical operations (decisions)
Acts as a gateway between primary memory and secondary storage
Registers
High-speed memory in the CPU
Program Counter (PC) - memory location address of instruction for
the next cycle performed by the CPU
Memory Address Register (MAR) - memory address of data to be
retrieved or stored or instruction to be executed
Memory Data Register (MDR) - holds data or instruction fetched
from memory or is about to be stored in memory
Current Instruction Register (CIR) - holds instruction currently being
decoded and executed
Accumulator (ACC) - stores intermediate results of the calculations
performed by the ALU
Cache
GCSE Computer Science Paper 1 (Topics 1–2) 2
