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3.1.4 - Hardware
Descrição
A Level Computing (F451) Mapa Mental sobre 3.1.4 - Hardware, criado por AndrewZV em 24-03-2014.
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3.1.4 - Hardware
Central Components of a Computer System
Arithmetic Logic Unit (ALU)
Performs two sort of operations on data:
Arithmetic
Addition
Subtraction
Multiplication
Division
Logical
Comparison
Less than?
Greater than?
Equal to?
Acts as a conduit through which all I/O to the computer is done.
Gateway to the processor.
Control Unit
Co-ordinates and controls all the operations carried out by the computer.
Operates by repeating three operations:
1. Fetch
Causes the next instruction to be fetched from main memory.
2. Decode
Produces signals which control other parts of the computer such as the ALU.
3. Execute
Causes the next instruction to be executed.
Memory Unit (RAM)
Quick and easily accessible information can be read from and written to by the Control Unit.
Access to and from the Memory Unit is very fast.
Normally contains:
Operating System (OS)
Software currently in use.
Data which the software is using.
Volatile
Data is lost when the computer is shut down.
Registers
An extremely fast piece of on-chip memory, for temporary storage.
The registers you need to know are:
Program Counter (PC)
Holds the address of the next instruction to be executed.
Memory Address Register (MAR)
Holds the address in memory of the location containing:
The next piece of data to be read.
The next instruction to be used.
Memory Data Register (MDR)
The contents of the address specified in the MAR are copied to the MDR. This may be:
An instruction/operation.
Data to be used (with an instruction).
Data to be copied to an address.
Current Instruction Register (CIR)
Holds the instruction while it is being decoded/executed.
The contents of the MDR are copied to the CIR if it is an instruction.
Contains the operator and the operand of the current instruction.
Status Register
Contains "status" bits or flags that are set or cleared based on the result of an instruction.
Accumulator
Works with the ALU to performs arithmetic functions.
Temporary storage areas.
Buses
A set of parallel wires connecting two or more components of the computer.
There are three buses:
Control Bus
Carries command and control signals to and from every connected device.
Fully bi-directional for all connected devices.
Address Bus
Communicates the physical addresses of computer memory elements/locations that the requesting device wants to access.
Data Bus
Transports the actual physical data to and from the memory.
Both single-directional and bi-directional.
Device Connectivity
Hard-wire (Physical)
Copper Coaxial
Fibre Optic
Copper Twisted Cable
Wireless (Non-physical)
Wifi
Satellite
Bluetooth
Measured in the rate at which data can be transmitted.
Baud Rate
Data rate can be increased by:
Using higher quality cable.
Less attenuation.
Increasing frequency at which data is sent.
Each signal can be sent on a different frequency or wavelength.
The number of frequencies that can be used before they interfere with each other is called the bandwidth.
Copper has low bandwidth.
Wireless has high bandwidth.
Fibre optic has very high bandwidth.
Memory
Main Memory
Random Access Memory (RAM)
Volatile (Wiped when the computer is turned off).
Used to store programs which are currently running.
Stores data which is currently being processed.
Read Only Memory (ROM)
Non-Volatile
Contents are permanently etched into the memory chip at the manufacturing stage.
Secondary Storage
Magnetic
Data recorded onto magnetic disks.
Mechanical parts move over the disk's surface to read and write data.
Advantages
Cheap.
Large storage capacity.
Disadvantages
Not portable.
Durability can be an issue.
Optical
Data is recorded onto optical disks.
Lasers read and write data.
Advantages
Highly portable.
Cheap.
Disadvantages
Low storage capacity.
Easily damaged.
Solid State
Data is recorded onto solid state memory chips.
Disadvantages
Expensive.
Less storage capacity than magnetic storage.
No mechanical moving parts.
Advantages
Fast.
Durable.
Transfer of Data
Fetch/Decode/Execute Cycle
Interrupts
A signal from some device or source seeking the attention of the processor.
The interrupt signal is sent along the control line to the processor.
The currently executing program is suspended and control is passed to an ISR (Interrupt Service Routine).
There is a register in the CPU called the Interrupt Register.
It is checked at the beginning of every F/D/E Cycle.
Buffers (Cache)
Used to help match the speeds of many devices.
Used between the high processing speeds of the CPU and the slower speeds of the Main Memory.
Data can be written to a buffer as though it were Main Memory.
The high speed processor can then carry out the next operation whilst the Main Memory reads from the buffer instead.
Anexos de mídia
Central_Components_of_a_Computer_System (image/png)
ALU (image/png)
Buses (image/png)
b92bba2764e6d8666c316edaba55b453 (image/png)
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