<aside> <img src="/icons/new-badge_green.svg" alt="/icons/new-badge_green.svg" width="40px" /> The new bit in this page is the new video added, and the removal of the section on registers, and a complicated version of the fetch-execute cycle.
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I felt a bit tired. Some parts of this page are largely inspired from BBC Bitesize…
The central processing unit (CPU) consists of six main components:
<aside> ⚙️ Control Unit (CU) - Fetches, decodes and executes instructions, it issues control signals that control hardware and it moves data (0s and 1s) around the system
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<aside> 📐 Arithmetic Logic Unit (ALU)
<aside> 📄 Registers
Registers are small amounts of high-speed memory contained within the CPU. They are used by the processor to store small amounts of data that are needed during processing, such as:
There was a section here with a list of specific registers. This has been removed in accordance to the specification.
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<aside> 🎞️ Cache
Cache is a small amount of high-speed random access memory (RAM) built directly within the processor. It is used to temporarily hold data and instructions that the processor is likely to reuse. This allows for faster processing as the processor does not have to wait for the data and instructions to be fetched from the RAM.
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<aside> 🚌 Buses
A bus is a high-speed internal connection. Buses are used to send control signals and data between the processor and other components.
Three types of bus are used:
<aside> ⏰ Clock
The CPU contains a clock which is used to coordinate all of the computer's components. The clock sends out a regular electrical pulse which synchronises (keeps in time) all the components.
The frequency of the pulses is known as the clock speed. Clock speed is measured in hertz (like physics!!). The higher the frequency, the more instructions can be performed in any given moment of time.
In the 1980s, processors commonly ran at a rate of between 3 megahertz (MHz) to 5 MHz, which is 3 million to 5 million pulses or cycles per second. Today, processors commonly run at a rate of 3 gigahertz (GHz) to 5 GHz, which is 3 billion to 5 billion pulses or cycles per second.
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CPUs are now very fast, but their performance can be affected by a number of factors (which you’ll need to know):
<aside> 🕰️ Clock Speed
Clock speed is the number of pulses the central processing unit's (CPU) clock generates per second. It is measured in hertz (like physics!!).
CPU clocks can sometimes be sped up slightly by the user. This process is known as overclocking. The more pulses per second, the more fetch-decode-execute cycles that can be performed and the more instructions that are processed in a given space of time. Overclocking can cause long term damage to the CPU as it is working harder and producing more heat.
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<aside> 🕰️ Cache size
The bigger its cache, the less time a processor has to wait for instructions to be fetched, since commonly used instructions are closer to where they need to be.
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<aside> 💯 Number of cores
A processing unit within a CPU is known as a core. Each core is capable of fetching, decoding and executing its own instructions.
The more cores a CPU has, the greater the number of instructions it can process in a given space of time. Many modern CPUs are dual (two) or quad (four) core processors. This provides vastly superior processing power compared to CPUs with a single core.
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In most computer systems, the CPU receives instructions and data from an input or memory. The instructions and data are processed by the CPU and the results are either sent to an output or transferred to secondary storage.
An Architecture is the specific design that enables the instructions and data to reach and be processed by the CPU. For example, phones and computers usually have different architectures, where phones prioritise power-saving, and computers are often faster/more powerful.