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Mr Levin Computer Science A-Level > A-Level > Flashcards

A-Level Flashcards

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1
Q

State what an algorithm is

A

A series of steps that are needed to be performed in order to perform a task

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2
Q

Why is it important for algorithms to be in the correct order?

A

So that it can run correctly without any errors

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3
Q

What is the purpose of a sub-step?

A

To break down a step in the algorithm so that it is clearer and easier to follow.

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4
Q

Most algorithms have 3 parts to it..They are.

A

Input. Process. Output

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5
Q

A condition in an algorithm…

A

allows for an algorithm to be solved in different ways.

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6
Q

Why use conditions in an algorithm.

A

It may make the task easier or faster to complete.

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7
Q

A condition in an algorithm is made up of three steps which are.

A

IF.THEN.ELSE

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8
Q

Another name for a condition is called…

A

Selection

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9
Q

Another name for a loop is

A

Repetition or Iteration

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10
Q

How many ways can you express an algorithm, and what are they?

A

3.

  1. Psuedo Code
  2. Structured English
  3. Flow Chart
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11
Q

What is the shape of an input/output in a flow chart?

A

Parallelogram

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12
Q

What is the shape for a condition/selection in a flow chart?

A

Kite

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13
Q

Which is the shape for a loop/repetition/iteration in a flow chart?

A

Eclipse

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14
Q

What is the structured english for assigning a value for giving someone the weight of 100

A

Set weight to 100

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15
Q

There are 3 ways to use negative numbers in Binary? What are they?

A

Magnitude
1’s Complement
2’s Complement

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16
Q

State the problems with using the magnitude method

A

It leads to calculation errors due to the fact it has a positive and negative zero.

It struggles to calculate positive and negative numbers.

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17
Q

State the difference between 2’s Complement and 1’s Complement Binary

A

2’s complement of a binary number is 1 added to the 1’s complement of the binary number.

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18
Q

State what is meant by Structured English

A

A subset of English Language that consists of command statements used to describe an algorithm.

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19
Q

State what is meant by Pseudocode

A

A way of using keywords and identifiers to describe an algorithm without following the syntax of a particular programming language.

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20
Q

State what is meant by Flowchart

A

Shapes linked together to represent the sequential steps of an algorithm

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21
Q

State what is meant by Assignment

A

A value is given a name (identifier) or the value associated with a given identifier is changed.

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22
Q

State what is meant by Selection

A

Under certain conditions some steps are performed, otherwise different (or no) steps are performed.

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23
Q

State what is meant by Repetition

A

A sequence of steps is performed a number of times. This is known as iteration or looping.

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24
Q

State what is meant by Input/Process/Output

A

Many problems we try to solve with a computer involve data which can be inputted, processed, or outputted.

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25
Q

State what is meant by BCD

A

Binary coded decimal (BCD) is a system of writing numerals that assigns a four-digit binary code to each digit 0 through 9 in a decimal (base-10) numeral.

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26
Q

When/Why do we use BCD?

A

Binary coded decimal has many important applications especially using digital displays. In the BCD numbering system, a decimal number is separated into four bits for each decimal digit within the number.

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27
Q

Describe how denary integers larger than 9 can be converted into BCD.
Give an example in your answer.

A

Each denary digit is written as a 4-bit binary number

• Example: 46 = 0100 0110

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28
Q

Describe how an 8-bit BCD representation can be converted into a denary integer.
Give an example in your answer.

A 
• Binary number is split up into groups of 4 bits (starting from the right)
 // Each group of 4 bits is converted to a denary digit
• Example: 0011 0111 = 37
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29
Q

Convert the following denary number into BCD format.

9 7

A

1 0 0 1 0 1 1 1

30
Q

Two disadvantages of using ASCII code.

A
  • Only 128 / 256 characters can be represented
  • Uses values 0 to 127 (or 255 if extended form) / one byte
  • Many characters used in other languages cannot be represented
  • In extended ASCII the characters from 128 to 255 may be coded differently in different systems
31
Q

Describe how Unicode is designed to overcome the disadvantages of ASCII.

A
  • Uses 16, 24 or 32 bits / two, three or four bytes
  • Unicode is designed to be a superset of ASCII
  • Designed so that most characters (in other languages) can be represented
32
Q

Explain what is meant by the character set of a computer

A
  • The symbols that may
    be represented/interpreted/understood by a computer
  • Normally equates to the symbols on a keyboard/digits, letters…
  • May include control characters
33
Q

Explain the use of a code used to represent a character set

A
  • Each character has a binary code/number…
  • …which is unique
  • Number of bits used for one character = 1 byte
  • Example code/ASCII/Unicode…
  • …use 8 bits per character/16 bits per character
  • Use of more bits for extended character set
34
Q

Describe what is meant by Unicode

A

 UNICODE is a coding system that assigns a unique code…
 …to all the possible symbols available throughout the world
 All symbols in different languages/platforms/programs have unique codes
 Continues to grow as it is not a fixed size set, currently over 100000 symbols represented.

35
Q

Why are bit patterns often displayed using hexadecimal instead of binary?

A

Easier for people to read/understand;
(Can be displayed using) fewer digits;
More compact when printed/displayed;

36
Q

What is meant by the resolution of a bitmapped graphic image?

What is meant by a pixel?

What is meant by Screen resolution?

A

The number of pixels/dots; per cm/inch/unit of measurement;

It is the smallest picture element which can be drawn

The number of pixels which can be viewed horizontally and vertically on the screen

37
Q

How many colours can a bitmapped graphic image with a colour depth of 4 bits contain?

A

16

38
Q

A bitmapped image has 16 x 16 pixels. It is stored in an image format that is limited to 65536 colours. Calculate the minimum image size in bytes.

A

512

39
Q

State two advantages of vector graphics compared to bitmapped graphics

A

(For geometric images) less storage space /memory likely to be needed;
(For geometric images) will load faster from secondary storage;
(For geometric images) will download faster;
Can be scaled/resized/zoomed without distortion // can be scaled/resized/zoomed without loss of quality;
Image can be (more easily) searched for particular objects;
Can (more easily) manipulate individual objects in an image;
Can preserve the background so that it can be recreated if an object is deleted;

40
Q

The ASCII system uses 7 bits to represent a character. The ASCII code in denary for
the numeric character ‘0’ is 48; other numeric characters follow on from this in sequence.
The numeric character ‘0’ is represented using 7 bits as 0110000.

Using 7 bits, express the ASCII code for the character ‘6’ in binary.

A

011 0110

41
Q

How many different character codes can be represented using 7-bit ASCII?

A

128

42
Q

State three items of data that would need to be stored about a circle object if it is to be represented using vector graphics.

A 
(Type of) shape // circle;
Coordinates of centre/midpoint;
Identifier;
(Length of) radius/diameter;
Line colour // outer colour;
Line width;
Fill colour // inner colour;
43
Q

Describe how an image can be represented as a bitmapped image in a computer’s memory.

A

The image is divided into pixels;
Each possible colour is represented using a bit pattern // each pixel is represented using the same number of bits;
Information is stored about the colour of each pixel;
The position of the pixel in memory determines its location in the image;

44
Q

Explain why text files and streamed videos may use different rates

A

 Text files use a small volume of data/Videos require large volume of data…
 In a small period of time if video is to be seen in real time/it will freeze or lag otherwise
 Consequently, number of bits per second is important/dependant on the data being sent
 Video data is time sensitive

45
Q

What is meant by lossless compression?

A

With lossless compression, every single bit of data that was originally in the file remains after the file is uncompressed. All of the information is completely restored. This is generally the technique of choice for text or spreadsheet files, where losing words or financial data could pose a problem. The Graphics Interchange File (GIF) is an image format used on the Web that provides lossless compression.

46
Q

What is meant by lossy compression?

A

Lossy compression reduces a file by permanently eliminating certain information, especially redundant information. When the file is uncompressed, only a part of the original information is still there (although the user may not notice it). Lossy compression is generally used for video and sound, where a certain amount of information loss will not be detected by most users. The JPEG image file, commonly used for photographs and other complex still images on the Web, is an image that has lossy compression. Using JPEG compression, the creator can decide how much loss to introduce and make a trade-off between file size and image quality.

47
Q

State the issues that you have with memory and development.

A

Computers are forever increasing performance - running programs. The processor needs to increase its performance of accessing the program and running the program.

There is a gap between access speeds which are slower than processor speeds. This needs to be closed if we can take advantage of processor speeds.

48
Q

State what is meant by memory

A

Memory = used for long term data storage. The processor can access this directly.

Memory = can be broken down into primary and secondary storage.

49
Q

Explain why people will struggle to have the best performing computers

A

Computer users would like to have a large amount of primary storage that costs little and allows quick access. This is not possible; the fastest components cost more and have limited capacity.

50
Q

State in order from slowest to fastest the different types of memory

A

Hard Drive
Solid State Memory
Physical Memory - RAM (SD RAM)
CPU CACHE (Processor)

51
Q

State in order from largest to smallest capacity in terms of memory

A

Hard Drive
Solid State Memory
Physical Memory - RAM (SD RAM)
CPU CACHE (Processor)

52
Q

State in order of price - cheap to expensive the different costings of memory

A

Hard Drive
Solid State Memory
Physical Memory - RAM (SD RAM)
CPU CACHE (Processor)

53
Q

Give 3 facts about RAM

A
  • Volatile memory (needs a constant electronic current to keep data)
  • Can be read from or written to any number of times.
  • Memory locations can be accessed at any location.
54
Q

State what is meant by D-RAM

A

DRAM - Dynamic RAM

DRAM - Constructed from capacitors which leak electricity and therefore needs regularly recharging every few milliseconds to maintain the data

55
Q

State what is meant by S-RAM

A

SRAM - Static RAM

SRAM is constructed from flip-flops which continue to store data indefinitely while the computer system is switched on

56
Q

State the differences between SRAM and DRAM

A

SRAM provides shorter access time than DRAM.

DRAM is less expensive to make and it can store more bits per chip and despite the needs for recharging it requires less power to operate.

57
Q

State how computers both use SRAM and DRAM

A

The norm is cache memory is for SRAM and main memory constructed from DRAM technology.

58
Q

Explain what is meant by ROM

A

ROM shares the random-access properties of RAM except it cannot be written to.

ROM is not lost when the computer is switched off; non-volatile memory.

ROM has specialised uses involving the data of programs that are going to be used unchanged over and over again.

ROM maybe programmable (PROM) or erasable (EPROM) or EVEN ELECTRICIALLY ERASABLE PROM (EEPROM). - this is at the manufacture stage.

59
Q

Describe the Physical Layout of the Hard Drive

A

Physical Layout of Hard Drive:

More than one platter (disk)
Each platter has a read/write head for each side
The platters spin in unison.
The read-write heads are attached to actuator arms which alow the heads to move over the surfaces of the platters
The motion of each actuator head is synchronised with the motion of the other heads
A cushion of air ensures that a head does not touch a platter surface

60
Q

Explain how the Hard Drive operates

A

Data is stored in concentric tracks.

Each track consists of a sequence of bits which are put into sectors

Each sector contains a number of bytes

The sector becomes the smallest unit of storage

To store a file, a sufficient number of sectors have to be allocated but these may or may not be adjacent to each other.

As files are created and subsequently deleted or edited the use of the sectors becoms increasingly fragmented which degrades the performance of the hard disk.
A defragmentation software program can reorganise the allocation of sectors which restores performance.

A hard drive is considered to be a direct-access read/write device because any sector can be chosen for reading or writing.

The Read Head uses the basic law of physics that a state of magnetisation will affect an electrical property
A Write Head uses the reverse law.
The 2 alternative states of magnetisation are interpreted as a 1 or 0.

61
Q

What could limit the potential of a hard drive?

A

The manufacturers have to deal with the fact that the physical length of a track increases from the innermost track to the outermost track.

If this fact is ignored then the hard disk will not reach its potential in terms of capacity.

62
Q

What in terms of development has been made to hard drives?

A

The storage capacity of disk drives has continued to improve and sizes have continued to shrink.
This improvement should carry on.

63
Q

State what is meant by frame rate

A

The number of images / frames recorded per second / unit time.
The frequency with which the images/frames are recorded.

64
Q

How is data READ on a CD-ROM?

A

Reading Data:

The disc spins and the laser beam is reflected from a surface.

The surface is a sandwiched between a substrate and a protective outer coating.

CD-ROMS use on the reflective surface both lands and pits.

When being read, the travel of the laser beam to a pit causes a difference in phase compared to reflection from a land.

The difference is recognised by the photodiode detector and attached circuitry and is interpreted as a 1 or 0.

65
Q

How is a DVD-RW/CD-RW written to?

A

For a CD-RW/DVD-RW technology, the reflective surface is a special ALLOY material.

When data is WRITTEN to the disc, the heat generated by the absorption of the laser light changes the material to liquid form.

Depending on the intensity of the laser light the material reverts to either a crystalline or an amorphous solid form when it cools.

66
Q

How is a DVD-RW/CD-RW read to?

A

When the disc is READ, the laser is reflected from the crystalline solid but not from the amorphous solid allowing the coding of a 1 or 0.

67
Q

How is an Optical device similar to a Magnetic device?

A

While the disc is spinning, the optical head that directs the laser beam is made to move so that the point of contact of the laser beam with the disc follows a single spiral path from the centre of the disc to the outside.

Despite only being 1 path, the formatting of data into sectors allows the disc to be used as a direct-access device just like a Magnetic Hard Disk.

Another similarity with the Magnetic Hard Disk is that the storage capacity is dependent on how close together individual physical representations of a binary digit can get.

68
Q

Explain the 2 factors that govern/rule how close binary digits can get

A
  1. If the disc is spinning at constant revolutions per second, the outer part of the disc travels faster than the inner part. (early technology countered this by spinning at constantly changing speed, keeping the bit density constant along the spiral path).
  2. The wavelength of the light controls how well the light can be focussed; the shorter the wavelength, the better the focus.

The original infrared diode laser used in a CD-ROM has much longer wavelengths than the red laser light used in a DVD.

The more recently used blue laser light has an even shorter wavelength. This change in wavelength is one of the reasons for the improvement in storage capacity.

69
Q

Explain what is meant by Solid State Memory

A

Solid state is a form of EEPROM (like ROM), however you can also program parts of it for normal use.

Solid state is a SEMICONDUCTOR technology with NO MOVING PARTS.

The circuits consist of arrays of transistors acting as MEMORY CELLS.

The most frequently used technology is called ‘NAND’ as the circuits resemble that of a NAND logic gate (we cover later!) as the memory cells are connected in a series.

70
Q

Explain how Data is Read/Written to Solid State Memory

A

Solid State has a special feature where the blocks of memory cells can have their contents erased all at once in a flash.

Before data can be written to a block of cells in the memory the data in the block first has to be erased.

When data is read, a whole block of data has to be read(loaded) in one operation.

The technology can be used for solid-state drives, which can replace hard disk drives.

The more frequent use is either a memory card or in a USB flash drive.

Mr Levin Computer Science A-Level (1 decks)

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