What is the CPU?
The central processing unit
Name the four main components in the CPU.
The Arithmetic and Logic Unit
The Control Unit
The Immediate Access Store
What does the ALU do?
- Performs all arithmetic processes
- Performs all logical process
- Acts as a gateway to the CPU
What does the control unit do?
It is the part the runs the fetch-decode-execute cycle.
What are registers?
They are a type of memory that can be accessed very quickly compared to other types of memory.
What do registers do?
They can be used to store data and control information during a fetch-decode-execute cycle or they can be used to hold values that are generated as part of the ALU working on data.
What is the Immediate Access Store?
The IAS is the place where programs and the data that is needed by programs are held, ready to be fetched then decoded and executed by the CPU. The CPU may also use this place to store the results of any processing it does. It can be thought of as made up of lots of individual 'memory' locations, each capable of storing a byte of data.
What affects to performance of the CPU?
- The materials the processor is made from
- The clock speed
- The size of data and address buses
- The word size
What meant by clock speed?
How fast the fetch-decode-execute cycles the CPU can be executed.
eg. 800Mhz means 800 million per second
What is meant by word size?
This is the number of bits that the CPU can work with in any one clock cycle. The more bits it can work with in one clock cycle, the faster the computer will go.
What is the program counter register (PC)?
this holds the address of the next instruction to be fetched and executd
What is the Current Instruction Register (CIR)?
this holds the current instruction being executed
What is the memory address register (MAR)?
this holds the RAM address you want to read to or write from
What is the memory data register (MDR)?
this holds the data you have read from RAM or want to write to RAM
What are the accumulators?
these hold the data being worked on and the results of arithmetic and logical operations
What is the status register?
this holds information about the last operation e.g. whether the least sum done produced a negative result
What is the interrupt register?
this holds details about whether an interrupt has happened
What is the address bus?
This bus, in black on the diagram, is usually a set of wires that links the CPU to the RAM (and to other places). If the CPU want to fetch an instruction from a particular address in RAM, or wants to write a piece of data to a particular address in RAM, it puts the address on the address bus
What is the data bus?
The dotted channels you can see in the diagram is the data bus. The CPU puts data it wants to transfer to RAM on this bus. If data is being fetched from RAM, then it is put on this bus as well.
What is the control bus?
Signals need to be sent around the computer to control when things happen. These signals are sent along the control bus. Tthe striped channel you can see in the diagram is the control bus.
What has to be considered when making interconnections?
What types of interconnection media are there?
What are Unshielded Twisted Pair cables (UTP)?
UTP is light, flexible and very cheap.
It is mainly used in homes to connect phone lines.
It consists of pairs of conductors covered in insulation material and then twisted together. Twisting reduces electrical interference at minimal cost.
The bandwidth for UTP isn't as high as for coaxial or fibre optic
What are coaxial cables?
They are made up of a central conducting core covered with some protective insulation. Wrapped around the insulation is a thin metal sheath that provides the electrical interference protection. Finally, the cable has an outer covering.
It is the cable that connects you tv to the aerial.
It is heavier and less easy to manipulate than UTP.
It is more expensive than UTP.
You can have longer cable runs than for UTP but still not as long as for fibre optic.
What is fibre optics?
This consists of a glass core wrapped in protection within a cable. Data is sent down the fibre optic cable as light, not electrical signals.
There is no electrical interference.
Fibre optic cables are also resistant to the effects of moisture because they are non-metallic.
Fibre-optic communications is high bandwidth compared to UTP and Coaxial.
The price of fibre optic cable has dropped rapidly in recent years so that it is comparable to metal-based cables. However, installing it and any modifications or repairs do need specialist engineers and this makes it relatively expensive to install and modify.
They are often used to connect servers to the main switches in a LAN network.
How would you set up a LAN?
You can use lasers to 'fire' data signals between different parts of a network or use radio signals to send information across a LAN.
Using radio signals and wireless cards in different devices Wi-Fi can be used to connect them.
What are MAC addresses?
Every wireless device has a Media Access Control Address. These addresses are needed when connecting a wireless network up.
To connect it you would have to log into the router using the admisitrator account and then add the address to the list of allowable MAC addresses.
This then allows this device to connect if it has the right password.
How are most wireless networks protected?
Most wireless networks are protected by a password, that usually has to have both numbers and letters and also use the most up to date WAP encryption techniques.
How are satellites used for communication?
A transmitter on the ground sends signals to a satellite using microwaves or some other form of transmission.
Using a different frequency to avoid interference, the signals are then redirected back to the planet.
If it doesn’t reach the intended recipient, it is then bounced to other satellites and on to its destination.
What are the pros of using a satellite for communication?
Satellites can handle a very high number of simultaneous communication lines as they can handle a large bandwidth.
Satellite communications can be used in the remotest parts of the world. One use of this technology has been to provide up-to-date educational materials for schools in remote parts of Africa.
The cost of data transfer is not dependent on distance it is dependent on how much you send.
What are the cons of using satellites for communication?
The equipment is very expensive.
Because of the distance between the surface of the planet and the satellites, there is a short delay in any communication.
Weather conditions can also affect the quality of transmission.
What is ethernet?
Ethernet is a widely-used design for baseband LANs, working until recently to speeds of up to 10 Mbps.
Now Fast Ethernet (also called 100Base-T) can achieve 100 Mbps and Gigabit Ethernet is faster still.
Ethernet networks connect stations using coaxial cable and can spread over about 100 meters although they can be extended with the right hardware.
Ethernet makes use of collision avoidance and collisation detection
How is it possible to reduce data collision on ethernet LANs?
Using a switched Ethernet LAN.
A switch can be used to split up the network into areas that improve the efficiency of communication
Two stations can also be given a temporary communication link between them using a switch, to ensure successful communication.
What is a dial up connection?
Dial up refers to connecting a device to a network via a modem and a public telephone network.
Dial-up access is really just like a phone connection, except that the parties at the two ends are computer devices rather than people.
What is an ISDN connection?
ISDN is an Integrated Services Digital Network.
The computer is connected to the ISDN line (which is usually just an extra normal phone line) with a 'special interface'. You don't need a modem because the connection is digital.
The ISDN line goes back to the digital part of the local PSTN exchange. The PSTN exchanges together form a digital network. Home computers with modems send and receive their information to start with using analogue connections to and from the analogue part of the exchange. Then the information is sent along the network using digital connections.
What is broadband?
ADSL (Asymmetric Digital Subscriber Line). It works by ‘splitting’ the telephone line into two. It then uses one half for phone calls whilst the other half is used for sending and receiving digital data, using many different frequencies at the same time. By sending different packets of data at the same time using different frequencies, a high bandwidth can be achieved.
What is a leased-line connection?
In this type of connection, you pay a fixed fee for a permanent Internet connection. You have access to the Internet 24 hours a day. You do not need to dial-up a phone number because you are always connected.
Leased lines typically give much higher bandwidths than modem connections and this may be necessary if there is heavy use in the office by a lot of people or use involving large multimedia files.
Name the different types of primary memory.
What is RAM?
Random Access Memory.
256 Mbytes of RAM means you have approximately 256 million individual memory locationsEach memory location has its own address and you can store an instruction or a piece of data in each location.
RAM is volatile. Re-booting the computer normally clears any corrupt data out of RAM.
What is ROM?
This holds the BIOS.
What is the BIOS?
- It checks that the computer hardware is present and correctly working.
- It runs a routine that looks for another special program called the bootstrap program. This is usually held in a special place on the hard drive. When it finds it, it loads it into RAM and runs it.
What does the bootstrap program do?
The job of the bootstrap program is to locate the operating system on the hard drive and then load it into RAM and run it. Starting up a computer from a power-off situation to where the operating system has been loaded up is known as 'booting up' the computer.
What is flash ROM?
Flash ROM allows a user to install an upgrade for their BIOS should the need arise.
This might happen because the existing BIOS cannot support some features that the user wants.
Whatever the reason, computer users can download and install another, later BIOS.
They simply need to identify their own motherboard and chipset and then identify a company who has written a new BIOS. They then have to download the BIOS and follow a set of procedures for getting it into their motherboard's ROM.
Why is the OS not stored in ROM on a PC?
The answer is flexibility. You should understand that you, the user, can't normally change the contents of ROM. If you wanted to change operating systems, for example, from Windows 98 to Windows XP, and the operating system was in ROM, you would be stuck! However, by putting the OS on the hard disk, you can upgrade it anytime you want and you don't need to change the program in ROM.
What are registers?
Registers are part of the design of the CPU. They are memory circuits and are very very fast because they are constantly being accessed by the CPU.
What is cache?
Fast access memory stored close/on the CPU.
Constantly-needed data is stored here as it is a lot faster to access than RAM (not as fast as registers).
It is very expensive and so there is only a small amount in computers.
What is battery packed RAM (CMOS)?
RAM with a battery attached to it, so that it never turns off, meaning the data isnt lost.
Part of the BIOS is stored in battery packed RAM so that it isnt lost and the user can put their own settings for boot up.
What is a buffer?
A buffer is an area of RAM that has been reserved for one purpose - to aid the transfer of data between different parts of a computer because those parts work at different speeds.
What is firmware?
The operating system of a peripheral in order to make it work.
It is normally stored in flash ROM in the device.
Name some examples of secondary storage.