1.1.1 Architecture of the CPU Flashcards
What is the CPU?
The processor or Central Processing Unit (CPU) is the internal hardware component of the computer that is responsible for executing the instructions of programs
what is the CPU made up of?
- arithmetic logic unit (ALU)
- control unit (CU)
- registers
what is the ALU?
The Arithmetic and Logic Unit (ALU) is the component of the CPU that carries out the following:
- Arithmetic calculations: addition, subtraction, division, and multiplication
- Logical operations: such as AND, OR, NOT
- Comparisons between values, such as greater than, less than, equal to
what is the CU?
The control unit organises the execution of instructions, including managing the other components in the processor.
The control unit is responsible for the following tasks:
- Ensures the execution of instructions in the correct sequence
- Decodes every instruction that the processor will execute
- Sends and receives control signals to and from other components
- Checks that signals have been delivered successfully
- Makes sure that data goes to the correct place at the correct time
The control unit also contains the clock. This is a tiny component that controls the rate at which instructions are executed in the processor.
what is the clock
The clock signal is used to synchronise the operations of the processor components. The system clock (also simply referred to as the clock) generates regular clock pulses by emitting a signal that continuously switches between a low (or ‘0’) and a high (or ‘1’) state.
The time taken between two sequential rising edges is called a clock cycle or a clock period. The clock speed is measured by the number of clock cycles in one second — 1 clock cycle per second is 1Hz.
Herz Measurement
1 hertz (Hz) 1 clock cycle
per second
1 million Hz megahertz (MHz)
1,000 MHz gigahertz (GHz)
what are registers?
Registers are locations of computer memory within the processor that provide extremely fast access.
General-purpose registers are used to store the results of the intermediate calculations that are part of larger computations.
Dedicated or special-purpose registers are processor-based registers that are used for a specific purpose.
- CIR
- MAR
- MDR
- PC
- Accumulator
What does the current instruction register (CIR) do?
Holds the current instruction that the processor is executing
what does the memory address register (MAR) do?
Temporarily stores the memory addresses used when searching for data in RAM
what does the memory data register (MDR) do?
Temporarily holds the data (data values or instructions) that are read from or written to the main memory
what does the program counter (PC) do?
Holds the address of the next instruction to be executed by the processor
what does the accumulator do?
Stores the result of any calculation
what is the fetch decode execute cycle?
The fetch-decode-execute cycle describes the basic operation of modern computers.
Instructions are loaded into memory (RAM) before the processor starts running the program
what is the fetch stage of the FDE cycle?
Each instruction is fetched from memory (in order), and put into the appropriate registers. The control unit can then access the instruction for the next stages
what is the decode stage of the FDE cycle?
The instructions (which are received in binary) need to be decoded before they can be run. This is the process the control unit uses to work out what the other components need to do.
Each processor will have slightly different encodings for instructions
what is the execute stage of the FDE cycle?
The control unit will tell the other components what they need to do in order for the instruction to work
