J276 - 1.1(B) - Factors That Affect CPU Performance

Which three are factors that affect CPU performance?

• Cache Size

• Clock Speed

• Number of Cores

• Number of Control Units

• Size of Memory Address Register

What is the cache?

• A small amount of memory inside the CPU that stores commonly used instructions.

• A small amount of memory outside the CPU that stores commonly used instructions.

• A portion of the Hard Disk Drive (secondary storage) that is used to hold instructions currently being worked on by the CPU.

• A register within the Random Access Memory, used primarily for storing instructions used each time the computer is switched on.

• A part of the CPU that often overheats from the amount of instructions it executes every second.

How does a small amount of Cache memory have a significant impact on the performance of a CPU?

• Commonly used instructions can be quickly accessed from within the CPU, meaning less time is required to fetch these from the RAM(main memory).

• Commonly used instructions can be quickly accessed from from the RAM(main memory) so less time is spent scanning the surface of the Hard Disk Drive.

• The CPU requires a steady supply of electrical current, and the Cache acts as a kind of well for this. By having a larger Cache, it means your computer can function for longer between small electrical power-outs.

• A larger Cache means that the CPU has almost a second form of RAM and this means twice as many instructions can be fetched, decoded and executed per cycle.

What is clock speed?

• The number of cycles per second, measured in Hertz (Hz).

• The speed with which the computer clock(the one that tells the time in the bottom right hand corner) is refreshed.

• The speed with which an individual instruction can be passed from RAM to the Memory Data Register.

• The number of bits (1s and 0s) that can be processed per second, measured in Hertz (Hz).

• The number of nibbles that can be processed per second, measured in Kilohertz (Hz).

The faster the clock speed...

• The more instructions can be fetched, decoded and executed in a given period of time.

• The easier it is to time the completion of a particular task by the CPU.

• The greater the chance of the CPU being overclocked and potentially being damaged.

• The less threads the CPU will be dealing with at any given moment in time.

A cycle is...

• Fetching, decoding and executing an instruction.

• Copying data from the accumulator and sending it back to the RAM (primary memory).

• Storing, decoding and fetching an instruction

• Thirty two 1s and 0s being stored in the registers of the CPU, ready to be processed.

Multiple cores are...

• Architecture where a single control unit works with several cores (the bits of a processor that actually carry out the instructions).

• Architecture where several control units work with more than one core (the bits of a processor that actually carry out the instructions).

• Architecture where there is more than one processor. Each processor is given its own dedicated chip of primary memory (RAM), to prevent data collisions.

• Is actually a misleading phrase. It actually means more than one control unit working with a single core(the bit of a processor that actually carry out the instructions).

A Dual Core Processor improves performance by...

• Each core simultaneously processing instructions (so the time required is almost halved).

• One core can work faster on a task because there is a redundant processor not having to be managed by the Control Unit.

• Each core is designed to be significantly quicker so together they will process more together.

• Bottlenecks of data are removed from the processor bus because they are being passed directly into each code.

The Program Counter

• Stores the address of the next instruction in memory

• Stores the address of where the next item will be fetched from

• Stores data fetched from memory, or waiting to be stored in memory

• Stores the result of arithmetic calculations

Memory Address Register (MAR)

• Stores the address of the next instruction in memory

• Stores the address of where the next item will be fetched from

• Stores data fetched from memory, or waiting to be stored in memory

• Stores the result of arithmetic calculations