Computer systems 1 The CPU Flashcards
Define a computer
A computer is a device that can be programmed to carry out general purpose mathematical and/or logical computations.
Define a system
A system is a combination of many connected parts all working together (interacting) to achieve a common goal.
Explain the interactions in a computer system
A computer system can be described as one that involves interaction between:
● Hardware is the physical components of a computer system, the computer components.
○ Examples: processor, memory, storage devices, any input or output device, peripherals, registers, logic gates etc.
● Software is the general term used to describe programs/instructions that are executed by the processor.
○ Examples: Any system software package e.g. microsoft word, steam, google.
● Data is the raw material or information that can be processed by any computing machine
● The (human) user
Define computer architecture
Computer architecture refers to how all the computer’s parts are physically, and logically, laid-out or connected.
Describe a basic von Neumann Architecture
Basic von Neumann Architecture
1. Central Processing Unit (CPU) carries out computations on data by following instructions, resulting in an output.
- Memory stores both the data to be operated on and the instructions (programs) that pirates on that data, and the results.
- A bus connecting the CPU and memory (represented by arrows)
- Input/output devices.
The motherboard is a circuit board that devices are physically mounted on. Motherboards typically include: the CPU, main memory, hard drive and many other components, such as I/O devices.
What is John von Neumann Known for?
John von Neumann (1903-57)
● Hungarian-American
● Outstanding mathematician, physicist, engineer and computer scientist.
● Described the architecture in 1945 - still relevant today.
What is a CPU and what does it do?
The Central Processing Unit (CPU) is the most important hardware component in a computer. It has two main functions:
● to process data and instructions
● to control the rest of the computer system
All programs and data processing are run in the CPU and all hardware components are, to some extent, controlled by it.
What are the six major components of the CPU
The CPU consists of 6 major components
● Control Unit (CU)
● Arithmetic Logic Unit (ALU)
● Registers
● Cache
● Clock
● Buses
What is the control unit? (CU)
The control unit directs the operations of the CPU.
● It fetches, decodes and executes instructions
● It issues control signals that control hardware
● It moves data around the system
What is the Arithmetic Logic Unit (ALU)
The Arithmetic Logic Unit (ALU):
● receives instructions (from memory) and data (again, from memory) and operates on the data according to the instructions.
● acts as a gateway between primary memory and secondary storage.
The ALU allows arithmetic (add, subtract etc) and logic (AND, OR, NOT etc) operations to be carried out.
What are registers? And give examples
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:
● the address of the next instruction to be executed
● the current instruction being decoded
● the results of calculations
MAR Memory Address Register
Holds the memory location of data that needs to be accessed
MDR Memory Data Register
Holds data that is being transferred to or from memory
ACC Accumulator
Holds the data being processed and the results of processing
PC Program Counter
Contains the address of the next instruction to be executed
CIR Current Instruction Register
Holds the instruction that is currently being decoded and executed
Explain what the cache is
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.
Explain what the clock is
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 all the components.
The frequency of the pulses is known as the clock speed. Clock speed is measured in hertz (Hz). The higher the frequency, the more instructions can be performed in any given moment of time.
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.
Explain what buses are and give examples
A bus is a high-speed internal connection. Buses are used to send control signals and data between the processor and other components.
Address Bus
Carries the addresses of data (but not the data) between the processor and memory
Data Bus
Carries data between the processor, the memory unit and the input/output devices
Control Bus
Carries control signals/commands from the CPU (and status signals from other devices) in order to control and coordinate all the activities within the computer. Also carries the clock’s pulses
What is the The Fetch-Decode-Execute Cycle?
When a program is being executed, the CPU performs the fetch-decode-execute cycle, which repeats over and over again until reaching the STOP instruction.
