Network Topologies
What is a Topology?
- The way in which the connections are made among all the computers is called the topology of the network.
- Network topology specifically refers to the physical layout of the network, specially the location of the computers and how the cable is run between them.
The most common topologies are:
Bus
Star
Ring
Mesh
Bus:
The bus topology is the simplest and most common.
It is often used when a network installation is small, simple, or temporary.
It is a Passive topology. This means that computers on the bus only listen for data being sent, they are not responsible for moving the data from one computer to the next.
- In an active topology network, the computers regenerate signals and are responsible for moving the data through the network.
- On a bus network, all the computer are connected to a single cable.
- When one computer sends a signal using the cable, all the computers on the network receive the information, but only one (Addressee) accepts it. The rest disregard the message.
Advantages of Bus:
1. The bus is simple, reliable in very small network, and easy to use.
2. The bus requires the least amount of cable to connect the computers together and is therefore less expensive than other cabling arrangements.
3. Failure of one node does not affect the rest of network.
Disadvantages of Bus:
1. Heavy network traffic can slow a bus considerably.
2. A break in the cable or lake of proper termination can bring the network down.
3. It is difficult to troubleshoot a bus.
Appropriateness of the bus topology:
- The network is small
- The network will not be frequently reconfigured
- The least expensive solution is required
- The network is not expected to grow much
Star Topology:
- In a star topology, each device has a dedicated point to point link only to central controller, usually called a hub/server/host.
- Each computer on a star network communicates with a central hub that resends the message appropriate computer(s)
- The hub can be active or passive.
- An active hub regenerate the electrical signal and sends it to all the computers connected to it.
Advantages of Star Topology:
1. It is easy to modify and add new computers to a star network
2. During adding/deleting a node network can function normally.
3. When the capacity of the central hub is exceeded, it can be replaced with one that has a larger number of ports to plug lines into.
4. Provide for centralised monitoring and management of the network.
5. Single computer failure do not necessarily bring down the whole star network.
Disadvantages of Star Topology:
1. If the central hub fails, the whole network fails to operate.
2. It cost more to cable a star network.
3. Require dedicated server and NOS
Appropriateness of Star Topology:
- It must be easy to add or remove client computer.
- It must be easy to troubleshoot.
- The network is large.
- The network is expected to grow in the future.
Ring Topology:
- In a ring topology, each computer is connected directly to the next computer in line, forming a circle of cable.
- It uses token to pass the information from one computer to another.
- Every computer is connected to the next compute in the ring, and each retransmit what it receives from the previous computer.
- The message flow around the ring in one direction.
- Ring is an active topology.
- There is no termination because there is no end to the ring
Token Passing method:
Token passing a method of sending data in a ring topology
A small packet, called the token passed around the ring to each computer in tern
If a computer has information to send, it modifies the token, adds address information and the data and sends it down the ring.
The information travels around the ring until it either reaches its destination or returns to the sender.
A token can circle a ring 200 meters in diameter at about 10,000 times a second.
Advantages of Ring Topology:
1. All the computers have equal access to the network.
2. Even with many users, network performance is even
3. Allows error checking, and acknowledgement.
Disadvantages of Ring Topology:
1. Failure of one computer can affect the whole network.
2. It is difficult to troubleshoot the ring network.
3. Adding or removing computers disturbs the network.
Appropriateness of Ring Topology:
- The network must operate reasonably under a heavy load
- A higher-speed network is required.
- The network will not be frequently reconfigured.
Mesh Topology:
- In a mesh topology, every devices has a dedicated point to point link to every other device.
- A fully connected mesh network therefore has n(n-1)/2 physical channels to link n devices.
- To accommodate that many links, every device on the network must have n-1 input/output ports.
Advantages of Mesh Topology:
1. Because of the dedicated link, no traffic between computers.
2. Failure of one node computer not affect rest of the network.
3. Because of the dedicated link privacy and security are guaranteed
4. Point to point links make fault identification and fault isolation easy.
Disadvantages of Mesh Topology:
1. Due to the amount of cabling and number of input output ports, it is expensive.
2. Large space is require to run the cables.
Variations of the Major Topologies:
1. Hybrid Star:
A star network can be extended by placing another star hub where a computer might otherwise go, allowing several more computers or hubs to be connected to that hub.
2. Star Bus:
The star bus topology combine the bus and the star, linking several star hubs together with bus trunks. If one computer fails, the hub can detect the fault and isolate the computer.
If a hub fails, computers connected to it will not be able to communicate, and the bus network will be broken into two segments that can not reach each other.
3. Hybrid Topologies:
Often a network combines several topologies as subnetworks linked together is a large topology.
For instance one department of business may have decided to use a bus topology while another department has a ring.
The two can be connected to each other a central controller in a star topology
When two or more topologies are connected together it forms a hybrid topology
Monday, July 26, 2010
Sunday, July 25, 2010
Nature and Types of Software
Software - is the collection of computer programs and related data that provide the instructions telling a computer what to do.
There are two types of software:
1. Systems software: the operating system.
2. Applications software: the programs we use.
Systems software:
is the control software that operates the hardware and allows the applications to run.
Operating Systems:
- Operating Systems run in the background without the users being aware of it.
- It controls the inputs, outputs, interrupts, and storage of files as requested by the applications software.
- examples is the windows XP operating System
Efficient Management of the Computer Resources:
1. Managing memory, i.e. allocating memory to more than one program running simultaneously. Some files may get moved to the hard drive temporarily. The place on the hard drive is stored in a directory for fast access when needed again.
2.Interrupts, for Enter, Printer out of paper, or a hardware or software malfunction.
3.Diagnostic checks on the system on Boot up, sending error messages where necessary.
4.Selecting and controlling peripheral devices through small Driver programs.
Utility Programs:
Systems software include other utility programs such as:
1. Systems software include other utility programs.
2. Virus checking and cleaning.
3. Security using identification and passwords.
4. File and hard disk management for efficiency and storage.
5. Customising the computer to the users requirements, i.e. short cut menus from mouse click.
6. Setting peripheral devices to the users requirements, i.e. setting the monitor resolution.
Types of Operating Systems:
1. Command driven: DOS.
- the user has to type in the command
- it has to be in the correct syntax, errors were common
- more adaptable than Windows when used by an experienced user.
2. Windows, Icons, Mouse and Pull down menus.
- originally developed by Apple for the Macintosh
- later developed by Microsoft for Windows 3.1.
- uses a mouse to click onto an icon to navigate to programs and files.
Applications Software:
Used for a specific purpose or application:
- Word processing;
- Numerical analysis and storage;
- Recording of data;
- Designing and graphics;
- Image processing;
- Presentations;
- Desk top publishing;
- Web design.
Three Groups of application Software:
1. Generic:
- general purpose for business;
- most common applications are Word Processing, Spreadsheet & Database.
- Most generic software for business comes in an integrated package such as: Microsoft Office, Lotus Smart-Suite, Coral Draw.
- The cost of the integrated package is much less than the sum of the separate applications.
- Microsoft Office is the most popular package used in business, it contains the applications: Word, Excel, Access, Power-Point, Front-Page.
2. Bespoke:
- tailor made, specifically written for a specific application.
- Software that is specially written for an application.
- An expensive but a perfect solution to a requirement when there is no suitable package available.
- Often a one off piece of software written for a large organisation as a perfect match to their needs.
3. Specific Task:
particular tasks for business;
most common are payroll, CAD, and stock control.
Appropriate Software Packages:
1. In business the software needs are most important and the hardware is purchased to accommodate the applications.
2. If the hardware is already in place, the software has to be able to run on it.
3. Is the cost within budget?
4. Should it be evaluated for appropriate use?
5. What problems did other users have?
6. Does it contain any known bugs?
7. Is it easy to install and get up and running?
8. What technical support comes with it, is any training available, is there good documentation?
9. What are the details of the licence agreement?
There are two types of software:
1. Systems software: the operating system.
2. Applications software: the programs we use.
Systems software:
is the control software that operates the hardware and allows the applications to run.
Operating Systems:
- Operating Systems run in the background without the users being aware of it.
- It controls the inputs, outputs, interrupts, and storage of files as requested by the applications software.
- examples is the windows XP operating System
Efficient Management of the Computer Resources:
1. Managing memory, i.e. allocating memory to more than one program running simultaneously. Some files may get moved to the hard drive temporarily. The place on the hard drive is stored in a directory for fast access when needed again.
2.Interrupts, for Enter, Printer out of paper, or a hardware or software malfunction.
3.Diagnostic checks on the system on Boot up, sending error messages where necessary.
4.Selecting and controlling peripheral devices through small Driver programs.
Utility Programs:
Systems software include other utility programs such as:
1. Systems software include other utility programs.
2. Virus checking and cleaning.
3. Security using identification and passwords.
4. File and hard disk management for efficiency and storage.
5. Customising the computer to the users requirements, i.e. short cut menus from mouse click.
6. Setting peripheral devices to the users requirements, i.e. setting the monitor resolution.
Types of Operating Systems:
1. Command driven: DOS.
- the user has to type in the command
- it has to be in the correct syntax, errors were common
- more adaptable than Windows when used by an experienced user.
2. Windows, Icons, Mouse and Pull down menus.
- originally developed by Apple for the Macintosh
- later developed by Microsoft for Windows 3.1.
- uses a mouse to click onto an icon to navigate to programs and files.
Applications Software:
Used for a specific purpose or application:
- Word processing;
- Numerical analysis and storage;
- Recording of data;
- Designing and graphics;
- Image processing;
- Presentations;
- Desk top publishing;
- Web design.
Three Groups of application Software:
1. Generic:
- general purpose for business;
- most common applications are Word Processing, Spreadsheet & Database.
- Most generic software for business comes in an integrated package such as: Microsoft Office, Lotus Smart-Suite, Coral Draw.
- The cost of the integrated package is much less than the sum of the separate applications.
- Microsoft Office is the most popular package used in business, it contains the applications: Word, Excel, Access, Power-Point, Front-Page.
2. Bespoke:
- tailor made, specifically written for a specific application.
- Software that is specially written for an application.
- An expensive but a perfect solution to a requirement when there is no suitable package available.
- Often a one off piece of software written for a large organisation as a perfect match to their needs.
3. Specific Task:
particular tasks for business;
most common are payroll, CAD, and stock control.
Appropriate Software Packages:
1. In business the software needs are most important and the hardware is purchased to accommodate the applications.
2. If the hardware is already in place, the software has to be able to run on it.
3. Is the cost within budget?
4. Should it be evaluated for appropriate use?
5. What problems did other users have?
6. Does it contain any known bugs?
7. Is it easy to install and get up and running?
8. What technical support comes with it, is any training available, is there good documentation?
9. What are the details of the licence agreement?
Sunday, July 11, 2010
CLASSIFICATION OF COMPUTERS ACCORDING TO SIZE,TECHNOLOGY AND PURPOSE
According to size
• Supercomputers
• Mainframe Computers
• Minicomputers
• Workstations
• Microcomputers, or Personal Computers
Supercomputers :
are widely used in scientific applications such as aerodynamic design simulation, processing of geological data.
• Supercomputers are the most powerful computers. They are used for problems requiring complex calculations.
• Because of their size and expense, supercomputers are relatively rare.
• Supercomputers are used by universities, government agencies, and large businesses.
Mainframe Computers:
are usually slower, less powerful and less expensive than supercomputers. A technique that allows many people at terminals, to access the same computer at one time is called time sharing. Mainframes are used by banks and many business to update inventory etc.
• Mainframe computers can support hundreds or thousands of users, handling massive amounts of input, output, and storage.
• Mainframe computers are used in large organizations where many users need access to shared data and programs.
• Mainframes are also used as e-commerce servers, handling transactions over the Internet.
Minicomputers:
are smaller than mainframe, general purpose computers, and give computing power without adding the prohibitive expenses associated with larger systems. It is generally easier to use.
• Minicomputers usually have multiple terminals.
• Minicomputers may be used as network servers and Internet servers.
Workstations
• Workstations are powerful single-user computers.
• Workstations are used for tasks that require a great deal of number-crunching power, such as product design and computer animation.
• Workstations are often used as network and Internet servers.
Microcomputers, or Personal Computers :
is the smallest, least expensive of all the computers. Micro computers have smallest memory and less power, are physically smaller and permit fewer peripherals to be attached.
• Microcomputers are more commonly known as personal computers. The term “PC” is applied to IBM-PCs or compatible computers.
• Desktop computers are the most common type of PC.
• Notebook (laptop) computers are used by people who need the power of a desktop system, but also portability.
• Handheld PCs (such as PDAs) lack the power of a desktop or notebook PC, but offer features for users who need limited functions and small size.
Personal Computers(PC):
According to Technology
• Analog Computers
• Digital Computers
• Hydride Computers
Analog Computers:
These computers recognize data as a continuous measurement of a physical property ( voltage, pressure, speed and temperature).
Example: Automobile speedometer
Digital Computers:
These are high speed programmable electronic devices that perform mathematical calculations, compare values and store results. They recognize data by counting discrete signal representing either a high or low voltage state of electricity.
Hybrid Computers:
A computer that processes both analog and digital data.
According to Purpose
1. General purpose Computers
2. Special Computers
General purpose Computers
A ‘General Purpose Computer’ is a machine that is capable of carrying out some general data processing under program control.
Refers to computers that follow instructions, thus virtually all computers from micro to mainframe are general purpose. Even computers in toys, games and single-function devices follow instructions in their built-in program.
Special purpose Computers
A computer that is designed to operate on a restricted class of problems.
Use special purpose computer equipment to obtain patient diagnostic information.
reference: http://wasaa.wordpress.com/2008/06/22/classification-of-computers/
• Supercomputers
• Mainframe Computers
• Minicomputers
• Workstations
• Microcomputers, or Personal Computers
Supercomputers :
are widely used in scientific applications such as aerodynamic design simulation, processing of geological data.
• Supercomputers are the most powerful computers. They are used for problems requiring complex calculations.
• Because of their size and expense, supercomputers are relatively rare.
• Supercomputers are used by universities, government agencies, and large businesses.
Mainframe Computers:
are usually slower, less powerful and less expensive than supercomputers. A technique that allows many people at terminals, to access the same computer at one time is called time sharing. Mainframes are used by banks and many business to update inventory etc.
• Mainframe computers can support hundreds or thousands of users, handling massive amounts of input, output, and storage.
• Mainframe computers are used in large organizations where many users need access to shared data and programs.
• Mainframes are also used as e-commerce servers, handling transactions over the Internet.
Minicomputers:
are smaller than mainframe, general purpose computers, and give computing power without adding the prohibitive expenses associated with larger systems. It is generally easier to use.
• Minicomputers usually have multiple terminals.
• Minicomputers may be used as network servers and Internet servers.
Workstations
• Workstations are powerful single-user computers.
• Workstations are used for tasks that require a great deal of number-crunching power, such as product design and computer animation.
• Workstations are often used as network and Internet servers.
Microcomputers, or Personal Computers :
is the smallest, least expensive of all the computers. Micro computers have smallest memory and less power, are physically smaller and permit fewer peripherals to be attached.
• Microcomputers are more commonly known as personal computers. The term “PC” is applied to IBM-PCs or compatible computers.
• Desktop computers are the most common type of PC.
• Notebook (laptop) computers are used by people who need the power of a desktop system, but also portability.
• Handheld PCs (such as PDAs) lack the power of a desktop or notebook PC, but offer features for users who need limited functions and small size.
Personal Computers(PC):
- Desk Top
- Lap Top
- Palm Top
- PDA
According to Technology
• Analog Computers
• Digital Computers
• Hydride Computers
Analog Computers:
These computers recognize data as a continuous measurement of a physical property ( voltage, pressure, speed and temperature).
Example: Automobile speedometer
Digital Computers:
These are high speed programmable electronic devices that perform mathematical calculations, compare values and store results. They recognize data by counting discrete signal representing either a high or low voltage state of electricity.
Hybrid Computers:
A computer that processes both analog and digital data.
According to Purpose
1. General purpose Computers
2. Special Computers
General purpose Computers
A ‘General Purpose Computer’ is a machine that is capable of carrying out some general data processing under program control.
Refers to computers that follow instructions, thus virtually all computers from micro to mainframe are general purpose. Even computers in toys, games and single-function devices follow instructions in their built-in program.
Special purpose Computers
A computer that is designed to operate on a restricted class of problems.
Use special purpose computer equipment to obtain patient diagnostic information.
reference: http://wasaa.wordpress.com/2008/06/22/classification-of-computers/
Computer Hardware General Overview
Hardware: The internal structure of computers, how they operate and how they are used in solving problems.
Programming -is about Software…why do we have to learn about Hardware and other stuff? Because we as computer students will be future doctors of computers and it is very essential to learn all about computers.
What is a Computer System?
What is it comprise of?
How would you define it?
Computer System is composed of two major factors.
1. Hardware
2. Software
Hardware=The physical components (electrical circuits) that make up the computer
Software=The computer programs (sequences of instructions) that tell the computer what to do in response to a command or some event.
Components of a Computer
INPUT DEVICES - For reading data into Main Memory
PROCESSOR - For processing the data
MAIN MEMORY - The program currently being executed is stored here.(it is divided into storage units called BYTES)
AUXILIARY STORAGE - For permanent storage of programs and data
OUTPUT DEVICES - For printing, displaying Or out-put of info
Think of the Brain (System)
1. INPUT - Study for exam
2. PROCESS - Understand and memorize information
3. OUTPUT - Results of the exam
Computer Systems are the same
Data is INPUT
Data is PROCESSED
Something is OUTPUT
*GIGO (Garbage in…Garbage out..)
Types of Computer:
1. Microcomputer
2. Minicomputers
3. Mainframe Computers
4. Supercomputers
Minicomputers:
- Multi-user systems
- 100’s of workstations or terminals attached to central minicomputer
- E.g. EPOS (Electronic Point of Sale) Systems
Mainframe computers
- Large Organisations –banks, building societies, airlines, governments
- May have 1000’s of terminals –geographically remote locations
- Could occupy a whole site
- 100’s of disk drives & hardware units
- Location often kept secret! (terrorist attacks)
Supercomputers
- Largest Category of computer
- Cost Millions
- Mostly used by scientific and industrial research departments
- NASA –government agencies
- Weather Centres
- Stock Exchanges
- Large Commercial Organisations
The processor:
- PROCESSES!
- Faster the processor, better the PC?
Brain of the computer
- Processes instructions
THREE STEPS:
1) Fetches Instructions
2) Decodes Instruction
3) Executes Instruction
CHIP:
A computer chip is an electronic circuit (consisting mainly of semiconductor devices, as well as passive components) that has been manufactured in the surface of a thin substrate of semiconductor material.
An electric circuit is made from different electrical components such as transistors, resistors, capacitors and diodes, that are connected to each other in different ways. These components have different behaviors.
The transistor acts like a switch
Resistor –resists electricity –so you can control current
Capacitor –controls electricity
Diode –also allows control of current and flow
Why Integrated Circuits (transistors)?
- Before –there were VACUUM TUBE
- They were huge
–costly
–bulky
–easily burned out
- The first Computer –ENIAC –huge 30 ton monster! *use of 18000 or so vacuum tubes*
A hybrid integrated circuit is a miniaturized electronic circuit constructed of individual semiconductor devices, as well as passive components, bonded to a substrate or circuit board.
MAIN MEMORY (MM):
- The program currently being executed and the data used by the program is held in MAIN MEMORY
- MM is divided into millions of individually addressable storage units called BYTES
- One byte can hold one character Or one byte can hold a code representing something –i.e a part of a picture, or a sound, or a program instruction.
The total number of bytes in MM = The computers MEMORY SIZE.
Computer Memory Sizes:
1 KB (KB) =1024 Bytes
1 MB =1024KB
1 GB =1024MB
1Tb =1024GB (about 1 trillion bytes)
RAM and ROM:
There are two kinds of Memory:
RAM
–Random Access Memory (MM)
- (this is used for storing programs that are currently running and data that is being processed)
- Main Memory
- Stores info about applications that are open and data
- VOLATILE = When you switch off the machine, it disappears!!!
ROM
–Read Only Memory
- (its contents are PERMANENTLY etched into the memory chip at the manufacturing stage. It is used –for example –to load the bootstrap loader (the program that loads as soon as you start the machine)
- Non-Volatile (does not change)
- Programs that are necessary for the computer to run
- Boot up program
- stores files and programs.
Cache Memory
- This is a very FAST type of memory that is used to improve the spped of a computer, DOUBLING it ….in some cases.
- Acts as an intermediate store between CPU and MM
- It works by storing most frequently or recently used instructions so that it is fast to retrive them again.
- Cache is usually between 1KB and 512KB
Disk Storage:
- Auxiliary storage is also called
- SECONDARY MEMORY
- BACKING STORE
- EXTERNAL MEMORY
- The most common secondary memory (auxiliary storage) is DISK!
Other types of Storage:
- Flash Memory Cards
- Sticks
- Floppy discs
- Disks
INPUT AND OUTPUT devices:
Input devices are the means whereby computers can accept data or instructions
Keyboards, magnetic strip cards, smart cards, magnetic ink character recognition devices,
Output –printer, VDU monitors, speakers, etc
Embedded Computers and special-purpose computers:
Not necessarily all computers are general purpose compuers with a screen, keyboard and disk drive. Special-purpose or dedicated computers can do all sorts of things from controlling the temperature in a greenhouse to controlling traffic lights or using a cash point. Embedded Computers are used in household goods automobiles and in industry
Programming -is about Software…why do we have to learn about Hardware and other stuff? Because we as computer students will be future doctors of computers and it is very essential to learn all about computers.
What is a Computer System?
What is it comprise of?
How would you define it?
Computer System is composed of two major factors.
1. Hardware
2. Software
Hardware=The physical components (electrical circuits) that make up the computer
Software=The computer programs (sequences of instructions) that tell the computer what to do in response to a command or some event.
Components of a Computer
INPUT DEVICES - For reading data into Main Memory
PROCESSOR - For processing the data
MAIN MEMORY - The program currently being executed is stored here.(it is divided into storage units called BYTES)
AUXILIARY STORAGE - For permanent storage of programs and data
OUTPUT DEVICES - For printing, displaying Or out-put of info
Think of the Brain (System)
1. INPUT - Study for exam
2. PROCESS - Understand and memorize information
3. OUTPUT - Results of the exam
Computer Systems are the same
Data is INPUT
Data is PROCESSED
Something is OUTPUT
*GIGO (Garbage in…Garbage out..)
Types of Computer:
1. Microcomputer
2. Minicomputers
3. Mainframe Computers
4. Supercomputers
Minicomputers:
- Multi-user systems
- 100’s of workstations or terminals attached to central minicomputer
- E.g. EPOS (Electronic Point of Sale) Systems
Mainframe computers
- Large Organisations –banks, building societies, airlines, governments
- May have 1000’s of terminals –geographically remote locations
- Could occupy a whole site
- 100’s of disk drives & hardware units
- Location often kept secret! (terrorist attacks)
Supercomputers
- Largest Category of computer
- Cost Millions
- Mostly used by scientific and industrial research departments
- NASA –government agencies
- Weather Centres
- Stock Exchanges
- Large Commercial Organisations
The processor:
- PROCESSES!
- Faster the processor, better the PC?
Brain of the computer
- Processes instructions
THREE STEPS:
1) Fetches Instructions
2) Decodes Instruction
3) Executes Instruction
CHIP:
A computer chip is an electronic circuit (consisting mainly of semiconductor devices, as well as passive components) that has been manufactured in the surface of a thin substrate of semiconductor material.
An electric circuit is made from different electrical components such as transistors, resistors, capacitors and diodes, that are connected to each other in different ways. These components have different behaviors.
The transistor acts like a switch
Resistor –resists electricity –so you can control current
Capacitor –controls electricity
Diode –also allows control of current and flow
Why Integrated Circuits (transistors)?
- Before –there were VACUUM TUBE
- They were huge
–costly
–bulky
–easily burned out
- The first Computer –ENIAC –huge 30 ton monster! *use of 18000 or so vacuum tubes*
A hybrid integrated circuit is a miniaturized electronic circuit constructed of individual semiconductor devices, as well as passive components, bonded to a substrate or circuit board.
MAIN MEMORY (MM):
- The program currently being executed and the data used by the program is held in MAIN MEMORY
- MM is divided into millions of individually addressable storage units called BYTES
- One byte can hold one character Or one byte can hold a code representing something –i.e a part of a picture, or a sound, or a program instruction.
The total number of bytes in MM = The computers MEMORY SIZE.
Computer Memory Sizes:
1 KB (KB) =1024 Bytes
1 MB =1024KB
1 GB =1024MB
1Tb =1024GB (about 1 trillion bytes)
RAM and ROM:
There are two kinds of Memory:
RAM
–Random Access Memory (MM)
- (this is used for storing programs that are currently running and data that is being processed)
- Main Memory
- Stores info about applications that are open and data
- VOLATILE = When you switch off the machine, it disappears!!!
ROM
–Read Only Memory
- (its contents are PERMANENTLY etched into the memory chip at the manufacturing stage. It is used –for example –to load the bootstrap loader (the program that loads as soon as you start the machine)
- Non-Volatile (does not change)
- Programs that are necessary for the computer to run
- Boot up program
- stores files and programs.
Cache Memory
- This is a very FAST type of memory that is used to improve the spped of a computer, DOUBLING it ….in some cases.
- Acts as an intermediate store between CPU and MM
- It works by storing most frequently or recently used instructions so that it is fast to retrive them again.
- Cache is usually between 1KB and 512KB
Disk Storage:
- Auxiliary storage is also called
- SECONDARY MEMORY
- BACKING STORE
- EXTERNAL MEMORY
- The most common secondary memory (auxiliary storage) is DISK!
Other types of Storage:
- Flash Memory Cards
- Sticks
- Floppy discs
- Disks
INPUT AND OUTPUT devices:
Input devices are the means whereby computers can accept data or instructions
Keyboards, magnetic strip cards, smart cards, magnetic ink character recognition devices,
Output –printer, VDU monitors, speakers, etc
Embedded Computers and special-purpose computers:
Not necessarily all computers are general purpose compuers with a screen, keyboard and disk drive. Special-purpose or dedicated computers can do all sorts of things from controlling the temperature in a greenhouse to controlling traffic lights or using a cash point. Embedded Computers are used in household goods automobiles and in industry
Subscribe to:
Posts (Atom)