Chapter 4 (Section 1) Final Revision #1

• Control Unit (CU) • Arithmetic and Logic Unit (ALU) • Immediate Access Store (IAS) • System clock • Buses • Registers

Instructions and data are stored in the same memory space (i.e. in main memory), so the CPU can fetch either from the same place using the same buses.

The ALU is the component in the processor that carries out all arithmetic and logical operations while a program is running. A computer can have more than one ALU.

They are carried out through sequences of addition, subtraction, and left or right shifting.

The ACC is a general-purpose register used to store numerical values temporarily at any part of a given operation or calculation.

• Coordinates / synchronises the actions of all other components in the CPU. • Sends and receives control signals along the control bus. • Manages the execution of instructions in sequence. • Controls communication between the components of the CPU and interprets instructions read from memory.

It generates timing signals that are sent along the control bus to synchronise the actions of all system components and prevent system crashes.

• The system clock gives out timing signals which are sent on the control bus to synchronise the other system components. • The Control Unit initiates data transfer by generating signals that are sent on the control bus to other components.

Measured in GHz. It represents the vibrational frequency of the clock — for example, 3.5 GHz means 3.5 billion clock cycles per second.

• Each instruction is executed on a clock pulse. • The clock speed dictates the number of instructions that can be run per second. • The faster the clock speed, the more instructions can be run per second.

Overclocking is increasing the clock speed beyond the factory setting. It can enhance speed but risks overheating, system instability, or crashes.

A core is a processing unit consisting of an ALU, a control unit, and registers. A CPU can contain multiple cores (e.g. dual-core has two, quad-core has four) to share workload.

• Each core processes one instruction per clock pulse. • With multiple cores, sequences of instructions can be split between them. • So more than one instruction can be executed per clock pulse. • More cores decrease the time taken to complete tasks.

A small, temporary storage location inside the CPU that holds data or instructions during the fetch-execute cycle. Registers can be general-purpose or special-purpose.

A register that holds data frequently used by the CPU and can be accessed directly by most instructions. Example: the Accumulator (ACC).

A register with a specific function within the CPU that holds program-status information; only used by certain instructions. Examples: PC, MAR, MDR, CIR, IX, SR.

• Special-purpose registers hold the status of a program; general-purpose registers hold the temporary data used while performing operations. • Special-purpose registers are specialised for a specific use; general-purpose registers can be used for any purpose. • General-purpose registers can be used by most instructions; special-purpose registers can only be used by certain instructions.

To store the address (memory location) of the next instruction to be fetched.