1.1 Components Flashcards
What is the CPU
Processor that has different components that enables it to carry out its task of executing instructions.
What components are in the CPU
CU
Buses
ALU
Registers
What does the CU do
Controls and coordinates the activities of the CPU
Directs flow of data between CPU and other devices
Accepts next instruction and decodes it into several steps (e.g fetching addresses and data from memory, managing its execution and storing the resulting data back in memory and registers)
What are buses
Set of parralel wires conecting two or more components of a computer together. Normally contains 8,16, 32 or 64 lines.
What are the three buses called
Data bus
Control bus
Address bus
What is the purpose of the buses in the FDE cycle (role of buses)
Address is sent to memory on the address bus when the CPU wants to access a part of memory
Data in that location is returned to the CPU on the data bus.
Control signals are sent on the control bus
What is the purpose of control lines
Ensure access to the data and address bus by different components does not lead to conflict
What is a bi directional bus
Carries signals in both directions
What is the purpose of a control bus
Transmit command, timing and specific status info between system components
What are some control line examples
Bus request (data bus)
Bus grant (data bus)
Memory write (Causes data on the data bus to be written in the addressed location)
Memory read (Causes data from the addressed location to be placed on the data bus)
Interrupt request (requesting CPU access)
Clock (Synchronises actions)
What is the purpose of the data bus
Provides bi directional path for moving data and instructions between system components
Transmits results of instruction to memory location
What is the purpose of the address bus
Transmits memory addresses of words that are used as operands in programming instructions so data can be retrieved and sent to processor
Width of the address bus determines max possible memory capacity of the system
What is a word
Fixed size group of digits, handled as a unit by processor. Different processors, different word sizes
The data bus transmits the data held in a word of memory, between processor and memory.
The largest operand that can be held in a word is related to the size of the data bus.
Purpose of ALU
Arithmetic and logic operations on data (e.g shift operations and Boolean logic operations)
What are registers
High speed memory cells. Arithmetic, logic and shift operations are temporarily stored here.
What is the accumulator
Used by some special purpose processors for simplicity.
Assumed all results of ALU are stored here.
What is the purpose of the PC
Holds address of next instruction to be executed
If next instruction is a branch or jump instruction the address to jump to is copied from CIR
What is the purpose of the CIR
Holds current instruction being instructed, split into operand and opcode
What is the purpose of the MAR
Holds address of the memory location from which data is to be fetched or which data is to be written to
What is the purpose of the MDR
Temporarily stores data read from or written to memory.
Also known as memory buffer register
What is the FDE?
Sequence of operations involved in executing an instruction .
The sequence is repeated as each instruction of the program is executed.
What are the steps in the fetch phase
1.Address of next instruction is copied from PC to MAR
2.Instruction held at address is copied to MDR.
3.PC is incremented so it holds address of next instruction
4.Contents of MDR
What are the steps in the decode phase
Instruction held in CIR is decoded. Instruction is split into opcode and operand.
What is the opcode used for
Used to determine the type of instruction and what hardware should be used to execute it
What can the operand contain
1.Address of data to be used with operation, which Is copied to MAR
2.Actual data to be operated on, copied to MDR (may be passed to the ALU)
What factors effect CPU performance
Clock speed
Number of cores
Amount of cache
What is the system clock
Generates a series of signals switching between 0 and 1, 7mil times per sec and synchronising CPU operations
Each operations starts as clock changes from 0 to 1
CPU can not perform operations faster than clock cycle (time clock takes to go from 0 to 1 to 0)
Greater the clock speed, the faster instructions will be executed.
What is a dual core processor
Two processors linked together in the same integrated circuit
Each core is theoretically able to process different instructions at the same time with its own fetch-execute cycle
Software might not always be able to take advantage of both processors
What is cache
Cache is small, very fast, expensive memory in the CPU
When an instruction is fetched from main memory it is stored into cache, so if it Is needed soon after it can be fetched from cache, which is quicker than going to main memory.
As cache is filled up older unused instructions or data is replaced with more recent ones
What are the levels of cache
Level1 Extremely fast (2-64KB)
Level 2 Fairly fast (256KB-2MB)
Level3 Some CPUs also have level3 cache
How is the von Neumann architecture organised
Shared memory, same bus used for data and instructions
Same word length is used for all memory
What is the stored program concept
Machine code instructions are fetched and executed serially by a processor that performs arithmetic and logic operations
A program must be resident in main memory to be executed
The machine code instructions are fetched from memory one at a time, decoded and executed to the processor.
How is Harvard architecture organised
Separates memories for instructions and data.
Used extensively with embedded Digital Signal Processing
Applications of Digital Signal Processing
Audio and speech signal processing
Sonar and radar signal processing
Biomedical signal processing
Seismic data processing
Digital image processing
What is the impact of having split memory
In embedded systems instructions may be held in read only memory while data memory requires read-write memory
Larger word size can be used for instructions
Instruction address bus may be bigger than the data bus
Instructions can be fetched in parallel, quicker
What are embedded devices + examples
Special purpose computers built into devices, often operating in real time
Examples:
navigation systems
aircraft flight control
traffic lights
simulators
Compare Von Neumann vs Harvard architecture
Von Neumann:
Used in conventional processors in PCs, servers and embedded systems with only control functions
Data and programs share memory
One bus is used to transfer data and instructions
Programs can be optimised in size
Harvard:
Used in digital signal processing and embedded systems, mobile communication systems, audio, speech and image processing systems
What are contemporary processor architectures
Modern high performance CPU child incorporate von neumann and haravard architectures by including one main memory but cache is divided into instruction cache and data cache.
Features of a complex instruction set
Used to accomplish tasks in as few lines of assembly language as possible.
Processor hardware is capable of understanding and executing sub tasks that make up a single instruction
The load/store instruction is stored with the instruction that carries out the actual calculation
Computer has little work to do to translate high level language into machine code
Little RAM is required to store instructions
Disadvantage is more specialised instructions had to be built into the hardware than needed
Features of a reduced instruction set computer (dw this ones shorter)
One simple instructions, taking one clock cycle, can be executed
Computer does more work translating from high level code to machine code
More RAM required to store machine code instructions
Pipelining possible
What Is a co processor
Extra processor that supplements the functions of the primary processor
What can a co processor be used to do
Perform floating point arithmetic
Graphics processing
Digital signal processing
What may a co processor not be able to do
Fetch its own instructions or do input and output operations
Generally it only carries out a limited range of functions
What is the advantage of multi core CPUs?
Distribute workload across multiple CPU cores, achieving higher performance
Examples of input devices
Barcode Readers (pen-type readers)
Laser Scanners
Camera based imaging scanner (decodes a 1D or 2D bar code, used for age verification and event ticketing)
CCD or CMOS (digital cameras)
Radio frequency identification (chipping pets, tagging items and smart codes)
Definition of an input device
An input device is one which can be used to put data and information into a computer
Definition of an output device
Hardware components that receive information from a computer system and present it to the user in a comprehensible form
Examples of output devices
Liquid Crystal Display monitors
Organic LED (brighter + thinner)
Laser printers
Inkjet printers
3-D printers
Projectors
Speakers
Features of secondary storage
Not directly accessible to the processor
Has slower access speeds
Retains content when computer power is turned off
How does a hard disk work
It uses rigid rotating platters with magnetic material and ions on the disk are polarised to a north (0/1) or south (0/1) state. Data is read when it moves across the drive head
Features of magnetic storage
Less portable - damage from movement
Large capacity
Slow down over time
Limited life span
Example of magnetic storage
HDD
Magnetic tape
Floppy disk
How does optical disk work
High powered laser “burns” sections of disks surface to make it less reflective. Reflective and non reflective areas are read as 1s and 0s
Features of optical storage
Generally durable, tho susceptible to scratches
Portable
Generally slower than other storage
Widely compatible
Example of optical storage
CDs
DVDs
Blu-ray
Features of solid state storage
Durable, no moving parts
Quick read/write speeds
Portable
Small and light
Expensive
Limited number of write/erase cycles
Examples of solid state storage
SSDs
USB Flash Drives
Memory Cards
Features of RAM
Stores programs and data being used
Volatile
What is held in ROM
Holds information needed to be stored permanently
e.g) bootstrap loader (starts up when computer us switched on and causes os to be loaded)
Embedded systems in washing machines, vehicles or cameras
What are virtual servers
Cloud-based or private off site servers that connect a local machine to the files you need via the Internet
What are the advantages of virtual storage
Reduced hardware costs
Improved reliability and performance
Flexibility ti scale storage requirements
What are the disadvantages of virtual storage
Relying on fast internet connection
Require back up plan I=with storage provider to keep data safe in event of hardware failure
Increasing fee depending on volume of storage being used
Loss pf functionality and compromise in the level of control you have over data
What ways are there to make a computer run faster?
Faster CPU
More RAM
Faster Secondary Storage
Update Os
Defragmentation
Check for viruses
What happens if there is a jump instruction?
CIR sends its address to the PC
How does the accumulator act as a buffer
Acts as a crucial link between inputs and outputs by holding results
What does the MDR do
Contains instruction which has been accessed from memory
Acts as a buffer: accommodates speed difference between memory and CPU
