Computer Science - General

Describe, with examples, two different types of data entry errors that a check digit would detect.

- 2 digits transposed - incorrect digit

Describe the properties of CD-ROM

- Can only be written to once - Single track - Uses a Red laser to read data

State two benefits of using USB connections between a computer and a device.

- Faster data transmission - Is supported by many operating systems

Properties of a proxy server

- Filters information (similarly to firewall and can act as a firewall) - Cache (stores recently visited websites to speed up access) - Keep user's IP secret

Describe the properties of an Compiler.

- Generates an error report at the end of translation of the whole program. - Translates the entire program in one go.

Rather than use a keyboard, a bank requests that a user use an on-screen keypad accessed with their mouse. The position of the digits on the keypad changes each time they visit the website. Explain why the bank has chosen to use this method of entering the 8 digits.

- If a keyboard isn't used, keyloggers will have difficulty gathering information on the code - The numbers are in random format, making it more difficult to interpret the mouse position

Describe the properties of DVD-RAM

- Many concentric tracks - Uses a Red laser to read and write data

TLS (Transport Layer Security)

- Newer, better encryption, authentication and data integrity - It is possible to extend it by adding new authentication methods - Can make use of session caching - Separates the handshaking protocol from the record protocol

Firewall weaknesses:

- No protection against individuals with their own modem - Employee misconduct - Stand alone computer disabling firewall

Security protocols

- SSL (Secure Socket Layer) - TLS (Transport Layer Security) - 2 Layers - Record protocol: Communication with/without encryption - Handshake protocol: Makes use of encryption algorithms

Describe the properties of Blu-ray

- Single track - Uses a Blue laser to read and write data

Describe the properties of DVD-RW

- Single track - Uses a Red laser to read and write data

Describe the properties of an Interpreter.

- Takes one statement at a time and executes it. - Stops the translation process as soon as the first error is encountered. - Slow speed of execution of program loops.

Modern LCD monitors and televisions use LED back-lit technology. Give two advantages of using this new technology compared to the older cold cathode fluorescent lamp (CCFL) method.

- Thinner monitors can be used. - No time needed to warm up.

Kamil is setting up a new computer system to record television programmes. He wants to be able to record, view and then erase programmes that he does not want to keep. He has chosen to use DVD-RAM as an optical storage medium. Explain to Kamil why it is better to use DVD-RAM rather than DVD+RW or DVD-RW.

- direct access because of concentric tracks - can read and write at the same time because it has a read/write head

Explain why a programmer would prefer to see the contents of the locations displayed as hexadecimal rather than binary, when debugging his program that reads the key presses.

- easier to identify values - easier to spot errors

Explain what the hex code in a MAC address represents.

- hardware/physical address - unique address/number associated (with network card in) a device/computer - usually 48/64 bits (12/16 hex digits) - first 6/8 digits = manufacturer code/ID of device (NIC) - last 6/8 digits = serial number of device (NIC)

Checksum

1 - Divide the sum, X, of the bytes by 256 2 - Round the answer down to the nearest whole number, Y 3 - Z = Y * 256 4 - Calculate the difference (X - Z) 5 - This value is the checksum

What are the 7 stages of the Von-Neumann fetch-execute cycle?

1 - The PC (Program Counter) contains the address of the next instruction to be fetched. 2 - The address contained in the PC is copied to the MAR (Memory Address register) via the address bus. 3 - The instruction is then copied from the memory location contained in the MAR and is placed in the MDR (memory data register). 4 - The entire instruction is then copied from the MDR and placed in the CIR (Current Instruction Register). 5 - The value in the PC is then incremented so that it points to the next instruction to be fetched. 6 - The address part of the instruction, if any, is placed in the MAR. 7 - The instruction is finally decoded and is then executed.

Describe the stages that take place when a user wishes to access a secure website.

1 - The web browser attempts to connect to a website which is secured by SSL. 2 - The web browser requests the web server to identify itself. 3 - The web server sends the web browser a copy of a its SSL certificate. 4 - The web browser checks whether the SSL certificate is trustworthy; if it is, then the web browser sends a message back to the web server. 5 - The web server will then send back some form of acknowledgement to allow the SSL encrypted session to begin. 6 - The encrypted data is then shared securely between the web browser and the web server.

Explain what is meant by the term "virus"

A program capable of replicating itself that deletes/alters data on a computer.

Describe how the sensors and the microprocessor are used to maintain the correct conditions in the fish tank.

Any four from: - information from the sensors sent to microprocessor - the ADC converts the analogue data into digital form - if temperature < 25oC OR temperature checked against stored value - ...microprocessor sends signal to heater/actuator/valve... - ...to switch on heater - if oxygen level < 20 ppm OR oxygen level checked against stored value - ...to open valve/oxygen supply - use of DAC between microprocessor and devices - sounds an alarm if system unable to respond - continuously monitors sensor inputs - any reference to feedback

Automatic doors in a building are controlled by the use of infrared sensors and a microprocessor. Describe how the sensors and the microprocessor are used to automatically open a door as a person approaches.

Any four from: - sensor(s) sends signal/data to microprocessor - signal/data converted to digital (using an ADC) - microprocessor compares signal/data with pre-set/stored value - if sensor(s) signal/data indicates the presence of a person / the door needs to be opened / a match is found / door is closed ... - ... microprocessor sends a signal to an actuator ... - ... to operate/drive a motor to open the door

Give a reason why the system asks for four characters chosen at random.

Any one from: - hacker never finds all characters on the first hack - makes it more difficult for hackers to find the order of the characters - hacker needs to hack the system several times to gain the whole password - shoulder surfing will not give person full password

What safeguards are needed to stop the fish tank temperature rising too high?

Any one from: - unsafe limit stored in memory - warning sound/signal if too high a value reached - fail safe switch off in case of a malfunction

Give three reasons for using a USB port.

Any three from: - automatically detects the hardware/installs drivers - plug only goes in one way/can't connect incorrectly - supports different data transmission speeds/a range of data transmission speeds - has become the industry standard/universally used - backwards compatible (with earlier versions of USB ports)

Solid state drives (SSD) are replacing hard disc drives (HDD) in some computers. Give three reasons why this is happening.

Any three from: - don't need to "get up to speed" to work properly/no latency - lower/less power consumption/more energy efficient - run cooler - run quieter - data access is faster - occupies less physical space/more compact - lighter, so more suitable for a portable computer/laptop - no moving parts so more reliable/durable in a portable computer/laptop

Explain why many web servers still use hard disc drive (HDD) technology.

Any two from: - HDD is cheaper for larger amounts of storage space - HDD has greater longevity for read/write functions - Expensive to change the technology // HDD are trusted technology - No requirement for the increased speed of SSD

Explain why it is more secure to use drop-down boxes rather than entering characters using a keyboard.

Any two from: - to protect against key logging software/spyware - can stop key presses being recorded - can stop key presses being relayed - drop down boxes cannot be recorded as key presses - drop down boxes can be placed in different location on the screen each time (to overcome screen capture issues)

Flash memories and CD-RWs are used as backing media for computers. Give two differences between these two media.

Any two from: Flash memory - solid state memory - no formatting issues - plugs directly into the USB port - direct transfer of data CD-RW - optical media - slower access speed/flash memory has faster access speed - requires a separate drive - data needs to be burnt/finalised/finished (before being used on another device)

State what is meant by the term "Serial data transmission"

Bits of data sent one at a time over one channel.

State what is meant by the term "Parallel data transmission"

Bits of data sent over multiple channels at the same time.

Give one benefit of Serial data transmission

Can be sent over longer distances.

Give one application of Serial data transmission

Connecting a computer to a modem.

Give one application of Parallel data transmission

Data bus within a computer.

Give one benefit of Parallel data transmission

Faster data transmission.

A _________ is used between the user's computer and the network to examine the data traffic to make sure it meets certain criteria.

Firewall

... The web server returns the selected webpage. The web browser reads the _____________ from the selected page and shows the correctly formatted page on the user's screen.

HTML tags/text

Name another type of printer and describe one way in which it is different from the printers named in part (b). Give an application for this printer.

Laser printer - uses toner/powder ink - uses (positive and negative) charged drums // rotating drum - uses static charge - no moving head - faster at printing - high volume output/high speed - producing flyers/leaflets/magazines

A user enters a URL. The web browser breaks up the URL into three components. Those components are:

Protocol//web server name/file name

To speed up the access to the web pages next time, a ______________ is used between the computer and the web server; this device uses a cache to store the website home after it has been accessed for the first time.

Proxy server

Explain what is meant by the term "Pharming"

Redirecting traffic from an official website to a fake one in order to steal personal info. (Malicious code on a user's hard drive or on the actual web server).

Name and describe one other measure that a bank could introduce to improve the security of the website.

Request username: additional security together with the PIN leaving the interceptor with more info required to gather.

Explain what is meant by the term "Phishing"

Sending legitimate-looking emails to a user asking for personal information in order to obtain private info. (Redirects user to fake website without their knowledge).

Session caching

Stores the TLS session to perform it again more quickly.

Describe the purpose of a Data bus

This bi-directional bus is used to exchange data between processor, memory and input/output devices.

Describe the purpose of a Control bus

This bus carries signals used to coordinate the computer's activities.

Describe the purpose of an Address bus

This uni-directional bus carries signals relating to memory addresses between processor and memory.

State what is meant by the term USB

Universal Serial Bus.

Ahmed sees the message "Set your browser to accept cookies". Explain why some websites make this request.

any two from: - to enable logon information to be kept on his computer - to provide pages customised for Ahmed the next time he logs on - to implement shopping carts and one-click purchasing - to be able to distinguish between new and repeat visitors to the website