What is BCD?
Binary coded decimal which is a way to represent decimal numbers in binary, where each digit is represented by a nibble(4-bit sequence). eg 364 would be 0011 0110 0100
How would you represent a negative number in binary?
Using either sign and magnitude or twos complement.
What is sign and magnitude?
A form of binary that shows both positive and negative, with the first bit representing the sign of the number. 0 is positive, 1 is negative. eg. 1001 = -1
What is twos complement?
A form of binary that shows both positive and negative numbers, where digits from bit 0 to the start of the set is written as it is and all others are inverted. eg. -12 = 11111100 in twos complement
What is an overflow error?
Where the result of operation is outside of the defined range. eg In binary addition where the addition of two number each in a single byte is larger than a byte and therefore two bytes are needed to store the result.
What disadvantage has sign and magnitude got?
You can't add + and - symbols together, therefore you end up with a wrong number during binary addition or subtraction using sign and magnitude.
How would you perform a binary subtraction?
Convert the number you're taking away to the opposite sign using twos compliment. Then add the two together.
What do you do when a carry occurs with two's compliment arithmetic?
1. When you add a positive to a negative you ignore the carry. 2. When adding two negative numbers you will always get a carry. Only ignore it if bit 7 is 0. 3. When adding two positive numbers you shouldn't get a carry. You check whether your answer is valid using bit 7.
What are subscripts used for in numbers?
The subscript shows what base the number is in.
eg. 10001010 is a denary number but 1000102 is binary
What is a nibble?
half a byte
Name the order for bits to petabytes.
How many bits are in a byte?
How many bytes are in a kilobyte?
What is a character set?
A defined list of characters recognized by the computer hardwareand software. Each character is represented by a unique binary number.
What is ASCII?
The American Standard Code for Information Interchange.
This is one of the two main recognised character sets, which is used on many personal computers.
Each character is represented by a byte.
7 bits are used for all the common characters used on a keyboard (128)
The 8th bit can be used as a check digit or used to further represent another 128 characters meaning ther character set would then have 256 characters.
What is EBCDIC?
The Extended Binary Code Decimal Interchange Code.
This is a character set used by older mainframe computers. This set uses different code to ASCII and therefore can't 'talk' directly to another PC.
This is only really used in big businesses and they are generally the only ones that use mainframes these days.
What is Unicode?
This is one of the two main recognised character sets, which is used on many personal computers.
It uses the same binary code as ASCII does for the 256 characters that ASCII covers, however unicode uses 16 bits, which allows it to cover many other symbols including that of other languages all around the world.
What is structured data?
Data that has a structure using paragraphs and indentation.
The purpose of the structured data is to make it easier to understand, however the more it is formatted the large the file size becomes.
What is free text?
Free text is a type of text that has no formatting applied to it. The only information is data and some spacing information.
This is useful for emails as it keeps the file size small and therefore is sent quickly.
What is transaction data?
Data that is collected automatically as it is generated and stored in a file, to be later processed.
What does data prepared offline mean?
It means that data is typed into a file and later on a process is run that uses the data in the file.
eg. forms with submit buttons
Describe a keyboard that would be used for manual input of data.
All keyboards have QWERTY keyboards and so are very efficient if the user has had relevant training.
A lot of work goes into designing keyboards ergonomically, which means they are designed in way that takes into account the limitations of human beings.
There also has to be consideration for health and safety due to Repetitive Strain Injury becoming more common.
Describe touch sensitive keyboards and concept keyboards that would be used for manual input of data.
Both concept and touch senstive keyboards have keys which are made up of touch sensitive areas on a plastic cover.
They also are easy to use for individuals that aren't computer literate as they keys can simply be images. The use of images can also speed up data input and reduce need of training.
The plastic cover can also be useful in settings where there is an excess amount of dust or dirt as it can stop it getting under keyboard keys and jamming the keys.
Describe touch screens that would be used for manual input of data.
A touch screen enables a user to touch their VDU screen to make selections.
This could be used in places where people need to find out information but may have no computer skills. They could also be used where fast decision have to be made.
Describe graphics tablets that would be used for manual input of data.
These are touch-sensitive pads that allow a user to draw on then with a stylus.
These are generally used by designers as they are more natural thatn using a keyboard and mouse to draw.
Describe mice that would be used for manual input of data.
A mouse is a pointing and selecting device used with a graphical user interfaces.
There are different mice around such as:
- standard 2/3 button mice
- mice with a scrolling wheel
- optical mice that dont collect fluff and dust
- mice that use radiowaves to connect to the computer instead
- ergonomically desgined mice
- mice that can work with a serial port
Describe data logging as a method for automatic input of data.
The process of using a computer to collect datathrough sensors, analyse the data and save and output the results of the collection and analysis.
What is an analogue-to-digital converter used for?
It is used as an interface between sensors used in data logging and the computer system.
It may perform other functions such as:
- converting analogue signals to digital
- acting as a switch
- providing compatible physical connections.
Describe optical mark readers as a method for automatic input of data.
Data sheets are prepared and marks are put in set places to indicate choices. Once the sheets are completed they can be scanned in automatically and the results produced straight away.
Describe optical character recognition as a method for automatic input of data.
A page is first scanned on a scanner. A very bright light is shone on the text and the white and dark space cause by the letters on the page reflet different amounts of light back.This is measured and used to produce a bit map picture of the writing. It is not yet a word processing document. Some OCR software is then run on the picture. This scans the picture looking for patterns that represent characters on a keyboard. As it finds these patterns, it transfers them to a text file. When the whole picture has been scanned, a text file will have been produced that can then be opened in a word processor. Although software is becoming ever more powerful, OCR is still only reliable for typed work. It still struggles to recognise handwriting.
Describe barcodes as a method of automatic data input.
The lines in a barcode represent data in coded form. This data held can be retrieved by using a laser scanner. The data obtained can then be used to look up further information held on computer.
Describe magnetic stripe cards as a method of automatic data input.
The magnetic stripe holds coded information that can be retrieved by swiping the card through a magnetic card reader.
They are quick to read and can be use many times.
They can be read but not written to.
Describe smart cards as a method of automatic data input.
Smart cards have an electronic chip in them.
This can be used to record each time a transaction occurs.
Smart cards can be written to as well as read from
Describe voice recognition as a method of automatic data input.
Using a microphone and some appropriate software, it is possible to input data into a computer.
The software is not perfect. You often have to teach it to recognise your voice accurately. If you have a cold, it may reduce the accuracy of input. Nevertheless, it is a fast way of inputting textual data and can greatly help someone with limited typing skills!
What is meant by validation.
Validation is the term used to ensure that only 'sensible' data is entered into a database. Sensible data means that it follows any validation rules set up for that field.
What is meant by verification.
Verification is checking that the sensible data you entered (which passed the validation rules set up fpr that data) is actually the data you meant to enter.
What are the six types of validation?
Name some data verification techniques.
- re-typing values
- re-typing whole data files
- reading back
- tick the box and click proceed
What should a back up policy include?
- The hardware/software that will be used to back-up a system.
- The person responsible for back-ups.
- The frequency that back-ups will be done.
- When they will be done.
- Where back-up copies will be kept.
- How back-up copies will be labelled.
- How the company will know the back-up system is working as it should.
A back-up strategy will also include details about when a full back-up of all files is to occur, and when an incremental back-up is to occur
What is an incremental back-up?
An incremental back-up is when the system only backs up files which have changed since the last back-up.
What media should data be backed up onto?
Magnetic tape is often used for backing-up networks because gigabytes of data can be stored on them. Servers often have a special piece of hardware in them that holds a number of magnetic tapes. The software that comes with it can be configured to automatically back-up data in the middle of the night and eject the tape ready for the network manager to put in the fire safe first thing in the morning.
What is archiving?
This is where data that is unlikely to be needed again but you cannot be deleted for legal purposes or other reasons is stored on a separate storage medium.