1) Alway add two key points, eg 'State two differences between ROM and RAM'
2) Use correct key words.
3) Use correct spelling when answering long questions.
4) Write workings out in the order of workings.
5) When describing an output, explain why it would be used for the SITUATION required.
6) Keep it simple, don't waffle.
7) Use the marks as a guideline of how many points I should include.
8) Learn basics keywords (sequences, iteration, statement)
9) Learn the different types of testing
10) Need to use the information to help answer the question.
11) 4 mark question, State, 'example', 'explantation'.
12) Follow the code when trying to solve something.
Thursday, February 26, 2015
Wednesday, February 25, 2015
Data Transmission
What is a network?
A network is collection of two oar more computers connected together to share resources.
LAN: Covers a small geographical area eg a single building in school.
WAN: Covers a large geographical area for example a country or continent.
Hardware
To build a network:
- at least 2 computers
- a network card
- network cable
- a switch or a hub to connect the cable to and exchange signals
- on large networks with a significant amount of traffic a network server is needed to mange data transmission.
Serial and parallel
Bits are sent one at a time over a single wire. The speed of transmission depends on the medium being used but could be very high (in some cases faster than a slow parallel transmission).
Parallel transmission is used inside computer systems and for very short distances. A parallel port could send 8, 16 or 32 bits simultaneously down separate lines. Before USB used to connect to printers.
Simplex
Is used for transmission of data in one direction eg from a mouse to a computer
Half-duplex
Used to transmit data in both directions but not at the same time.
duplex modes
Is used for transmission of data in both direction simultaneously.
Bit rat
The number of bits transmitted each second or the rate at which data is transferred.
Different bit rates are suitable for different applications. Largely based on how time sensitive the information is.
Video streaming - requires a high bit rate as there is lots of data and any delay will interrupt the video
Transferring word documents - Can use a lower bit rate as the files are needed on real time and people can wait a few min for the files to arrive.
Errors in data transmission
Its very easy for data to become corrupted during transmission. There are three main ways that computers check for errors in data.
Echoing - back The receiver sends the data back to the sender who checks that it matches what was originally sent.
Check sums - Extra digits or numbers are added to the end of a complex sequence. These numbers are calculated based on the number in the sequences. When the sequence in received the check number ins recalculated and if it doesn't match then the data is resent.
Parity check - 1 bit in each byte is reserved as the parity bit. The parity bit is 1 if the number of 1s in the rest of the byte is add 0 if the number of 1s is even.
Packets - When data is transmitted across a network the whole file is not sent at once. the files is broken up into a smaller chunks called packets and these are transmitted separately across the network.
Once a file has been broken up in to packets each packet has a header added to it, this contains information like the packets sender, destination, size and the protocol it it using.
Transmitting data in packets instead of whole files is more reliable and more secure.
Circuit switching - all the packets take the same route to their destination
This means that it is quick to assemble packets at the receiving end as they arrive in the order they were sent.
Packet switching - All the packets take different routes to their destination. This means that it takes longer to assemble packets at the receiving end as they dont arranging the order they were sent. However packets can also avoid slower areas of the network to avoid overloading the network.
Peer to peer - making connection to together computers with equivalent class with your network.
Bit rat
The number of bits transmitted each second or the rate at which data is transferred.
Different bit rates are suitable for different applications. Largely based on how time sensitive the information is.
Video streaming - requires a high bit rate as there is lots of data and any delay will interrupt the video
Transferring word documents - Can use a lower bit rate as the files are needed on real time and people can wait a few min for the files to arrive.
Errors in data transmission
Its very easy for data to become corrupted during transmission. There are three main ways that computers check for errors in data.
Echoing - back The receiver sends the data back to the sender who checks that it matches what was originally sent.
Check sums - Extra digits or numbers are added to the end of a complex sequence. These numbers are calculated based on the number in the sequences. When the sequence in received the check number ins recalculated and if it doesn't match then the data is resent.
Parity check - 1 bit in each byte is reserved as the parity bit. The parity bit is 1 if the number of 1s in the rest of the byte is add 0 if the number of 1s is even.
Packets - When data is transmitted across a network the whole file is not sent at once. the files is broken up into a smaller chunks called packets and these are transmitted separately across the network.
Once a file has been broken up in to packets each packet has a header added to it, this contains information like the packets sender, destination, size and the protocol it it using.
Transmitting data in packets instead of whole files is more reliable and more secure.
Circuit switching - all the packets take the same route to their destination
This means that it is quick to assemble packets at the receiving end as they arrive in the order they were sent.
Packet switching - All the packets take different routes to their destination. This means that it takes longer to assemble packets at the receiving end as they dont arranging the order they were sent. However packets can also avoid slower areas of the network to avoid overloading the network.
Peer to peer - making connection to together computers with equivalent class with your network.
Wednesday, January 7, 2015
Representation Of Data and Binary
All digital data are stores as binary. Eg Words, Cameras, Monitors...
When converting binary into decimals or reverse the left side is the most significant bit and the right side is the least significant bit.
8 bits = 1byte
BCD is when we code each part of the data by using a nibble.
By using Sign Magnitude method we loose a bit meaning the biggest number we can store is 127.
2a Complement
We assume that the MSB is a negative and the rest of the bit is positive adding to the negative number.
Three way of coding
EBCDIC is dead, stores data on a magnetic tape. cannot store keyboards characters.
ASCII every keyboard character is given a corresponding binary code. every letter is given a binary number.
UNICODE uses 2 bytes it is replacing ASCII it is used to cover more languages in the world, it is more important in the internet as it can store more languages.
When converting binary into decimals or reverse the left side is the most significant bit and the right side is the least significant bit.
8 bits = 1byte
BCD is when we code each part of the data by using a nibble.
By using Sign Magnitude method we loose a bit meaning the biggest number we can store is 127.
2a Complement
We assume that the MSB is a negative and the rest of the bit is positive adding to the negative number.
Three way of coding
EBCDIC is dead, stores data on a magnetic tape. cannot store keyboards characters.
ASCII every keyboard character is given a corresponding binary code. every letter is given a binary number.
UNICODE uses 2 bytes it is replacing ASCII it is used to cover more languages in the world, it is more important in the internet as it can store more languages.
Monday, December 1, 2014
How Internet Works
- It is an wire that has connections to computers and servers
- Each server has IP address that has a given name.
- Anything we get from the internet are files that are stored in the servers hard disk that are connected to the internet.
- DNS which allows us look up the IP address for any particular name.
- The computers are connected to ISP that is connected to the wire.
- When pictures are sent they are split into smaller sections called packets.
- Everything connected to the internet has a IP.
Wednesday, November 26, 2014
Array
NUMERIC DATA TYPES
This is an integer, so whole number eg 7 or a Real number so 7.2.
ALPHANUMERIC DATA TYPES
This is a CHAR so single character or digit, eg ‘C’.
String, several characters together, like star citizen.
BOOLEAN
Data that can only take two values so true or false.
ARRAY OF DATA
contains several data items, usually of the same type, grouped with a single name. Accessed using an index, Stored continuously within computer memory.
continuously means like all together, in sequence.
In Python an array is called a list.
If you have a list/array you can easily add things to the list and take away from the list without changing the source code on the fly. This also allows more flexibility with using it other than storing each one as a separate variable.
li = ['a', 'b', 'new', 'mpilgrim', 'z', 'example', 'new', 'two', 'elements']
for item in li:
if item == 'example':
print "this is an example function"
for item in li:
if item == 'example':
print "this is an example function"
This will go through the list until it finds “example” and it will print the text.
a one dimensional array as one row whereas a two dimensional array has an unlimited amount of rows and columns, similar to a spreadsheet.
all arrays start at position 0
so in: M A R A D; M is in position 0 and A is in pos 1
0 is still the first character/part of the array.
An array is used to make a program more efficient when it comes to a lot of data, it is also good for iteration as it means you can eliminate using each variable separately. Arrays are dynamic.
Wednesday, November 19, 2014
Wednesday, November 12, 2014
System Life Cycle
1) Problem
2) Analyse the Problem
3) Design
4) Implementation
5) Test
6) Install
7) Maintain
8) Evaluate (Goes back to 1)
Waterfall and Spiral
Waterfall is the traditional one which only goes through the system life cycle once
The Spiral is when the system life cycle carries on.
Waterfall
Information Gathering
Interview This is time consuming bit allows us to probe for answers and get first hand information
Questionares
This is useful when there are lots of users although there is a limit to how much you will find out.
Observe the Current System
Although time consuming this is objective rather than subjective and might spot things that the user doesn't.
Feasibility Study is a report to identify the possible solutions to the problem and how possible they are.
Economic or technical feasibility of the new system.
Importance of Analysis
2) Analyse the Problem
3) Design
4) Implementation
5) Test
6) Install
7) Maintain
8) Evaluate (Goes back to 1)
Waterfall and Spiral
Waterfall is the traditional one which only goes through the system life cycle once
The Spiral is when the system life cycle carries on.
Waterfall
Information Gathering
Interview This is time consuming bit allows us to probe for answers and get first hand information
Questionares
This is useful when there are lots of users although there is a limit to how much you will find out.
Observe the Current System
Although time consuming this is objective rather than subjective and might spot things that the user doesn't.
Feasibility Study is a report to identify the possible solutions to the problem and how possible they are.
Economic or technical feasibility of the new system.
Importance of Analysis
- Problem must be accurately defined to solve it effectively
- User may not understand potential of computer system
- Developer not likely to understand the industry which the user working in
- Developer must produce a solution that the user requires to meet their needs
- clear communication between the user and developer is important
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