1 - Components of a Computer Flashcards
What components does the CPU have to enable it to carry out its task of executing instructions?
Control Unit
Buses
Arithmetic Logic Unit (ALU)
Dedicated Registers.
What is the Control Unit? What tasks does it carry out?
The Control Unit unit directs the operations of the CPU.
Tasks it carries out:
Directs the flow of data between CPU and other devices.
Accepts the next instruction.
Decodes instructions.
Stores resulting data back into memory.
What are buses?
A bus is a set of parallel wires connecting two or more components of a computer.
The width of the bus is the number of parallel wires the bus has.
What is the system bus?
The address bus, control bus and data bus make up the system bus.
What is the data bus?
A bi-directional bus (data is carried in both directions). It’s used for transporting data and instructions between components.
What is the address bus?
This is the bus used to transmit the memory address specifying where data is to be sent to or retrieved from.
The width of the address bus determines the maximum possible memory capacity of the system. e.g If it was 32 lines it would only have 2^32 memory locations (4,294,967,296).
What is the control bus?
A bi-directional bus used to transmit control signals between internal and external components. The control bus coordinates the use of address and data buses and provides status information between system components.
Control signals include:
Bus Request: Indicates that a device is requesting the use of the data bus.
Bus Grant: Indicates that the CPU has granted access to the data bus.
Memory Write: Causes data on the data bus to be written into the addressed location.
Memory Read: Causes data from the addressed location to be placed on the data bus.
Interrupt request: Indicates that a device is requesting access to the CPU.
Clock: Used to synchronise operations.
What is the arithmetic logic unit?
The ALU completes all the arithmetical and logical operations. It can perform instructions like subtract, multiply, divide on fixed or floating point numbers.
Can also perform: shift operations, boolean logic and operations (and, or, not xor).
What are Registers?
Registers are small memory cells that operate at a very high speed. They’re used to store data and all arithmetic, logical and shift operations occur in these registers.
What are the registers and their purpose?
Program Counter - Holds the address of the next instruction to be executed.
Accumulator - Stores the results from calculations.
Memory address register - Holds the address of a location that is to be read or written to.
Memory data register - Temporarily stores data that has been read or data that needs to be written.
Current Instruction Register - Holds the current instruction being executed, divided up into operand and opcode.
Explain the Fetch-Decode-Execute Cycle.
It’s a sequence of operations that are completed in order to execute an instruction.
Fetch:
- Address from the PC is coped to the MAR.
- Instruction held at the address is copied to MDR by the data bus.
-Simultaneously, the contents of the PC are increased by 1.
- The value held in the MDR is copied to the CIR>
Decode:
- The contents of CIR are split into operand and opcode.
Execute:
- The decoded instruction is executed.
What is clock speed?
● Clock speed is determined by the system clock
● All processor activities begin on a clock pulse
● Each CPU operation starts as the clock changed from 0 to 1
● The clock speed is the number of clock cycles completed in a second.
What are cores in a CPU?
A core is an independent processor that can run it’s own fetch-execute cycle. More cores = more fetch-execute cycles at any given time. However, not all programs utilise multiple cores efficiently.
What is Cache memory?
Cache memory is the CPU’s onboard memory. Instructions fetched form main memory are copied to the cache, so if required again, it can be accessed quicker. As cache fills up, unused instructions are replaced.
Explain the different levels of cache.
Level 1 cache is extremely fast but small.
Level 2 cache is fairly fast and medium sized.
Level 3 cache is much larger but slower memory cell.
What is pipelining?
Pipe lining is a technique to improve processor performance. It’s the process of completing the fetch, decode and execute cycles of three separate instructions simultaneously, holding appropriate data in a buffer in close proximity to the CPU until it’s required. While one instruction is being executed, another can be decoded and another fetched.
Its aim is to reduce the amount of the CPU which is kept idle.
