Components of a Computer- S1 Flashcards
The Central Processing Unit
the CPU or the processor, has a number of different components which enables the it to carry out its task of execution instructions.
Control unit
controls and coordinates the activities of the CPU It accepts next instructions and decodes it
Bus
a set of parallel wires connecting two or more components of a computer
The processor is connected to the main memory by three busses known as the system bus. Only one signal can be transmitted along a bus at a time.
Address Bus
The address bus transmits the memory addresses so that data can be retrieved and sent back to the processor. Data can only be sent one way (CPU to memory)
Data bus
The data bus, provides a bidirectional path for moving data and instructions from memory to location. (carries data between register components)
Control Bus
transmits control signals (from the control unit) to the rest of the processor (commands, timing) Data is a bi-directional bus between, CPU to memory or I/O devices.
Arithmetic-Logic Unit (ALU)
performs arithmetic and logical operations on the data. E.g subtract, shift operations within a register, Boolean logic operations.
Acts as a conduit through which all I/O to computer is done/gateway to the processor.
Fetch phase
1) The address of the next instruction is copied from the PC to the MAR
2) The instruction held at that address is copied to the MDR, and 1+ is added to the PC so it holds the address of next instruction.
3) The contents of the MDR are copied to the CIR.
Decode phase
The instruction in the CIR is decoded. The instruction is split into the opcode and the operand (the data that will be operated on).
Opcode
the instruction
Operand
the data that will be operated on
Registers
Provide fast access to data for when frequent access is needed like in the fetch execute cycle. It is used for temporary storage.
Memory Unit
Stores OS Stores data (currently in use) Stores software(currently in use)/boot program/operations/instructions.
Difference between RAM and ROM
- RAM is volatile/ROM is not volatile
- RAM is editable/ROM cannot be altered
- RAM is larger/ROM is smaller
Whats stored in RAM
Programs, software and data in use so that it can be accessed faster than the hardrive
What software is stored in RAM
Bootstrap, must be available when computer switched off in order to start the computer
Program Counter
-Is needed to store the address of the next instruction
-Value is then sent to the MAR
-After sending the value the PC is incremented
-OR the PC changes to address
held in CIR if the operation is a Jump
Memory Address Register
Contains the address of the instruction sent from PC
or sent from CIR
Memory data register(MDR)
- Contains the instruction which has been accessed from memory
- That is referenced by the MAR
- Instruction sent to CIR
- MDR acts as a buffer
Accumulator(ACC)
Temporary storage that holds data being used during
calculations. It deals with input & output in the processor.
Current instruction Register(CIR)
holds the current instruction being executed. Which is divided into operand and opcode.
Name two architecture you can get for processors
The von Neumann and Harvard architecture
What is the architecture of the Von Neumann
A program must be resident in main memory to be executed
Instructions are fetched from memory one at a time, decoded and executed in the processor.
There will be a CPU, Arithmetic Logic Unit and main memory (RAM).
Data bus transfers data and instructions, so instruction fetch and a data operation cannot occur at the same time
An address bus transfers addresses and instructions.
Problems with the Von Neumann architecture
The data bus is slower than the rate at which the CPU can perform instructions and the speed of the processor is limited by the data transfer (bottleneck).
Harvard Architecture
- Instructions and data are held in separate memories
- Parallel data and instruction buses may be used
- Programs tend to be large
- The CPU can be fetching both instructions and data at the same time.
- Harvard can be faster the von Neumann
What two types of Instruction Sets can you get?
CISC (Complex Instruction Set Computers)
RISC (Reduced Instruction Set Computers)
CISC
Has a large instruction set to to accomplish tasks in as few lines of assembly language as possible. Complex instructions are built into the machine’s hardware.
RISC
One instruction performs a simple task and there is only a limited number of instructions available. Therefore complex tasks can only be performed by combining multiple instructions.
Difference between CISC and RISC
RISC has…
Has simpler hardware
More complicated software code
Takes one cycle per instruction (pipelining is possible)
Uses more RAM to handle intermediate results
More to compile
Used in smartphones and tablets, as they need less power and less energy. whereas CISC used in PCs
Whats an instruction set
all the instruction in machine code that are recognised and executed by the CPU
What two types of systems can be used for a processor
Co-processor and multi-core
Co-processor
Designed to carry out specific task, usually floating point calculation,graphics and digital signalling processing, which would take up a lot of processor time.
Multi-core`
Multi-core CPUs can distribute workload across multiple CPU cores, achieving higher performance. This is used in supercomputers when there is a lot of processing needed
When will multi-core not work?
When a problem/operation can not be broken down and distributed
Input
Inputs consist of data or commands that enter the computer system.
Output
Where the information obtained after processing is presented to the user. It might be something you see, hear, smell, read.
What is an Actuators
motors in conjunction with sensors to control a mechanism like opening windows, starting pump, turning a wheel
Storage Device
Storage devices are secondary storage and are used to store data and software for later. It is not directly accessible to the processor like RAM and has a slower access speed, but it retains its contents when the computer it turned off.
Give examples of Storage Devices
Hard Drive, Magnetic Tape, CD/DVD, USB/Flash memory,
Out of CIR, MDR and PC which hold binary numbers?
All of them
Out of CIR, MDR and PC which always hold only an address
PC
Out of CIR, MDR and PC which can change more than once during a cycle
PC and MDR
Out of CIR, MDR and PC which may pass a value to the MAR
PC and CIR
Give the name of the computer architecture that uses fetch-execute cycle with a single control unit
Von Nueman architecture
Explain once other advantage excluding cost of RISC compared with CISC
RISC runs faster due to simpler instructions
Describe three different input devices used by police
Fingerprint scanning- digitises image and compares with those held in database.
DNA analysis looks for similarities in DNA in two samples.
Cameras (security in shops) which record.
