Set 4 Flashcards
Checked by Matt. Covers everything between SA3 and CAP1 on the BPCompSci topic list (74 cards)
1
Q
What is a barcode?
A
- A barcode is a sequence of parallel black and white bars with varied width and spacing that encodes binary information
- Sometimes a check digit is added to the end of the barcode for validation
2
Q
Describe the operation of a barcode reader:
A
- A laser is directed at the bar code
- A prism moves the light beam across the bar code
- Some of the light is reflected back
- The black and white bands reflect different amounts of light
- The light sensor measures the amount of reflected light
- The light reflected is converted into an electrical signal
3
Q
What are QR codes? How are they different from regular barcodes?
A
- Two-dimensional barcodes
- They have a higher storage capacity
- QR codes are read using images, not lasers
4
Q
Describe the operation of a digital camera:
A
- Light enters through the lens, focused on to an array of sensors on the sensor chips
- Grid of (pixel) sensors // CMOS/CCD sensor
- Each sensor measures light intensity of a point
- Each sensor produces an electrical signal
- The signal represents a pixel;
- Sensor outputs a voltage dependent upon light intensity
- Colour/Bayer filter is applied to generate separate data values for red, green and blue colour components
- The pixels are recorded as an array
- Voltages turned into binary data
- Image processing software analyses image
5
Q
Describe the operation of a laser printer:
A
- A bitmap of the image is built in memory from the page description.
- A negative charge is applied to the photosensitive drum.
- A laser beam is directed at the drum.
- A mirror is used to direct the laser beam.
- Where the laser strikes the drum, the charge is neutralised.
- A negative charge is applied to the toner.
- The toner sticks to drum based on the charge
- Some paper is passed over the drum and the toner transfers to it.
- The positively charged transfer roller assists the transfer of toner from the drum to the paper.
- The heater fuses the toner onto the paper.
- For colour printing, four different colour toners / drums are required.
6
Q
What does RFID stand for and what is its purpose?
A
RFID (radio frequency identification) allows data to be transmitted wirelessly over radio waves.
7
Q
What are the two parts to an RFID system?
A
Tag
Reader
8
Q
What is in a passive RFID tag?
A
- chip, which contains a small amount of memory
- antenna
9
Q
Describe the operation of RFID
A
- RFID tag contains transmission circuitry and antenna
- Memory on tag stores data
- RFID reader transmits signal
- Signal activates RFID tag
- RFID tag transmits by radio wave
- RFID reader converts radio wave back into binary data
- RFID tag on a card is a passive device
- RFID transmits over very short range
10
Q
Advantage of RFID over barcodes or digital cameras
A
The use of radio signals means that the system does not require a line of sight between the tag and the reader
11
Q
What is a passive RFID tag? Range?
A
- An RFID tag that doesn’t contain a power supply
- The device is powered by radio energy transmitted by the reader
- Range of up to 1m
12
Q
What is an active RFID tag? Range?
A
- An RFID tag that has a small battery within the tag
- The tag will transmit its identifier at regular intervals
- Range of up to 200m
13
Q
Why is secondary storage is needed:
A
- To store data / programs whilst the computer is turned off as the contents of RAM are lost when the computer is turned off R. ‘main memory’ for ‘RAM’
- Allows the storage of data sets / files that could not fit in RAM
- Secondary storage can be used for virtual memory
- To transfer data / programs between computers
14
Q
What type of storage are Hard Disk Drives?
A
Magnetic storage
15
Q
What are the parts of a HDD?
A
- at least one metal platter
- a spindle which spins the platter
- a read-write head on an actuator arm
16
Q
Describe the operation of an HDD:
A
*Disk is coated in a magnetisable material
*Magnetising a spot in one direction could
represent 0 and the other direction could
represent 1
*Disk divided into rings called tracks
*Tracks divided into sectors / blocks
*Read/write head moves in / out to the correct track
*Wait until correct sector passes under read/write head
*Disk spins at high speed
*Read/write head senses magnetic field
and converts to 0s and 1s
17
Q
Give pros of a HDD:
A
- High read-write access speed (but slower than SSD)
- Greater Capacity than SSD
- … at a lower cost per GB than SSD
- Reliable and don’t degrade over time
18
Q
Give cons of HDDs:
A
- Not as portable as CD/DVD/USB memory sticks
- HDDs are more likely to fail as they are made up of lots of moving parts
- HDD’s are fragile (bumps and knocks damage disk)
- Slower access speeds that SSDs (slow seek time)
19
Q
What type of storage are Solid State Drives?
A
solid state storage / NAND flash memory
20
Q
Describe the operation of an SSD:
A
- Data is stored electronically
- Data is stored in floating gate transistors
- electrons are trapped between oxide layers
- Presence of trapped electrons / charge or absence indicates 0 / 1
- NAND flash memory is used
- Data is organised into pages / blocks
- A whole block of data must be written to
- A block must be erased before it can be overwritten
- Controller manages the organisation
21
Q
Give pros of SSDs compared with HDDs:
A
- Faster than HDD
- No moving parts means it is more robust than HDD
- No moving parts means it uses less power than HDD
- No moving parts means it is quieter than HDD
22
Q
When is an SSD suitable?
A
- When files need to be read or changed frequently (e.g. in a server)
- Or when the system needs to be portable
23
Q
Give cons of SSDs compared with HDDs:
A
- The number of times SSD devices can be written to is limited (hence unsuitable for long term archiving of data)
- Higher cost per Gb than HDD
24
Q
What kind of storage do optical drives use?
A
Optical storage (e.g. CD, DVD, BluRay)
25
Name optical discs (e.g. CD)
- Compact Disc (CD)
- Digital Versatile Disc (DVD)
- Blu-ray Disc
26
Name the types of optical drive (e.g. ROM):
- **ROM** (read only)
- **R** (recordable)
- Can be written onto once. Good for archiving data
- **RW** (rewritable)
- Has a chemical dye layer on top of the reflective layer
- The chemical dyes allow the burning process to be reversed
27
Describe the operation of an optical drive:
**How data is represented**
* Data is stored on one spiral track
* Continuation of land/pit reflects light whereas transition between land and pit scatters light
* Transition between land and pit indicates a 1 and continuation of land/pit represents 0
**Reading mechanism**
* Low power beam of laser is shone at disk
* Light is focussed on spot on track
* Some light is reflected back from disk
* Amount of light reflected back is measured
* Disc spins at constant linear velocity
28
Give pros of optical discs:
1. Extremely light and portable
... so they are good for media distribution
2. Relatively cheap (for lower storage capacities)
3. Reliable (unless scratched)
29
Give cons of optical drive:
3 points.
Any 3 from:
1. Data can be ruined if disc is scratched
2. Lower capacity than HDD and SSD
3. Slow seek time
4. Not all disks are rewritable
5. Not compatible with very much anymore
30
What is a composite key?
A key composed of two or more attributes that together uniquely identify a record.
31
When is normalisation (database) achieved?
* When there is no redundant data and all related data is stored together
* *(When each attribute depends on the key, the whole key and nothing but the key)*
32
What is the saying for databases to be fully normalised?
"Each non-key attribute must depend on the key, the whole key, and nothing but the key"
33
What are the requirements for 1st normal form?
1. Every record has a primary key
2. **No repeating groups** → must include a copy of the primary key in the new table (creating a *composite key*)
3. The data in each field must be **atomic** (i.e. data cannot be sensibly subdivided e.g. name → fname & sname)
34
What is a repeating group?
A set of attributes whose structure repeats between rows
35
Requirements for 2nd normal form
No partial dependencies
this means...
- Do all non-key attributes depend on **all parts** of the composite key?
- If not, take them out and create a new entity.
(*So check all tables with composite keys*)
36
Requirements for 3rd normal form
No non-key dependencies
- All non-key attributes are checked to see if they are **only** dependent on the primary key.
37
How do you signify the key in an entity description?
e.g. StudentID is the key for this entity:
Students(StudentID, FirstName,Surname,Age)
Underline the key
38
Give the SQL command for: Selecting from two tables
SELECT table1.attributeX , table2.attributeY
FROM table1 , table2
WHERE table1.primarykey = table2.foreignkey
AND ...
39
What is application software?
Give two examples.
Application software is designed to perform tasks a user wants to complete.
Any 2 from:
word processors, spreadsheet software, movie editing, game, web browser, calculator etc.
Examples must not use brand names such as Google Chrome3
40
What is system software?
Software used in the management of a computer system that abstracts the user from how the computer works
41
What are utility programs?
Software that performs a non-core management function for a computer
42
Give four types of system software
Operating System
Utility Programs
Libraries
Translators
43
Give three examples of utility programs
virus checker, disk defragmenter, backup, compression, encryption software etc
**R**. examples that relate to core functions of the operating system
**R**. examples that are application software
44
What are libraries?
* Libraries are precompiled, pretested routines (sets of code) that other programs can link to and use
* As long as the programmer includes a **reference** to the library in their code, they can access all the functions of the library
45
How do libraries save developers time?
* Common tasks can be written as libraries for **repeated use**
* This saves time for developers as it saves them from having to rewrite the instructions
46
What are translators?
Translators are **systems software tools** that are used to convert program code from one format into another, **without adjusting the logical operation** of the original program code
47
Name the three types of translator
Compilers, Assemblers, Interpreters
48
What is the purpose of compilers?
To turn program source code into a target language version (eg machine code / bytecode) that can be executed by the computer
49
What is the purpose of assemblers?
- To turn low-level assembly language code into executable machine code
- They are very fast to run
50
How do interpreters work?
Interpreters run instructions from a **high-level language** by determining what actions should occur **line-by-line** and executing **equivalent prewritten executable code.**
51
Why is the operating system classified as systems software?
It is required for the **functioning/maintenance** of the system itself, and performs tasks that are machine oriented
52
Give the characteristics of a low-level language:
* They are **defined by the processor** they are designed to run on
* **Non portable** - they are **specific to the instruction set** of the processor they are written for
* They are **machine-oriented** and have **no built-in functions**
* There is a **one-to-one** mapping between a low-level language instruction and its equivalent machine code language instruction
53
Why are low-level languages non-portable?
They are specific to the **instruction set** of the processor they are written for
54
What two things make up a low level instruction?
- **Opcode** - an **represents the machine operation** that the processor should perform
- **Operand(s)** - a value or set of values relevant to the opcode
55
Give the three things the operand of a low level instruction can be, and what addressing mode is used in each case
- memory locations (**direct (memory) addressing**)
- register values (**direct (register) addressing**)
- actual decimal values (the operand is the datum) (**immediate addressing**)
56
Why is hexadecimal used in some low level languages?
- Binary machine code is difficult for humans to **debug and fix** problems in.
- So hexadecimal is usually used instead, as it is **easier to read and understand**
57
What is assembly code?
- A low-level language that uses a **set of mnemonics** that represent **binary machine code instructions**
- Assembly code is converted into machine code using an **assembler**.
58
Give three characteristics of high-level languages
- High-level languages are **problem oriented**
- **Portable** - not specific to any type of processor
- One instruction in a high-level language **represents many instructions** in a **low level** language
59
What is an imperative language?
* A language where a problem is solved by writing a **sequence of instructions** that are followed in order
* Instructions describe **how** to carry out a task // each instruction is a step
* Instructions can **change the state** of the program
60
Give the advantages of high-level languages:
3 points.
Any 3 from:
1. Program code is easier to understand/maintain/debug
1. Faster development time
1. Programs are more portable to other hardware platforms
1. Availability of flow control structures
1. Improved features for supporting modularity
1. Built-in support for data structures
1. Language is problem-oriented
1. Support for different paradigms
61
Give the pros of low-level languages:
1. Assembly language code may execute more quickly
**R**. If response suggests that faster execution is because translation is not required
1. Assembly language code may use less memory
1. Assembly language gives direct/better access to computer hardware // enables direct manipulation of memory (contents)
**NE**. “More efficient” for either executes more quickly or uses less memory
62
What is a low-level language?
* A language that is based upon the instruction set of a processor
* They are defined by the processor they are designed to run on
63
What is immediate addressing?
- When the operand value is an actual value/datum that is part of the instruction
- There is no need to go to any memory address in this case
64
Give three advantages of compilers (over interpreters):
* The source code cannot be accessed by users
* Users do not need to have an interpreter to the run the program
* The program will execute more quickly
65
Why is code that will be executed in a **web browser** often **interpreted** rather than **compiled**?
* It's impossible to know what type of processor will be in the user's computer
* A compiled program will only execute on a processor of a **specific instruction set**, whereas interpreters can execute on a computer with any type of processor
66
Why are translators necessary?
* High-level instructions cannot be **executed directly**
* Processors can only **execute machine code** instructions
67
How do compilers and interpreters approach errors differently?
* Compilers analyse the program as a whole, and will not translate any of the program if it encounters an error
* Interpreters analyse the program on a line-by-line basis, and execute until the first error is encountered
68
Give an example of an intermediate language and how its used
* Bytecode
* Compilers convert high-level code into bytecode, and then use a **virtual machine** to execute the bytecode on different processors
69
What is the difference between source code and object code?
* Source code is the input to a translator
* Object code is the output of a translator
70
Explain the relationship between hardware and software
- Software is the programs that execute on the hardware
- Hardware is the physical components that allow the software to execute
71
What does computationally secure mean for a cipher?
A cipher is computationally secure if it cannot be cracked in ‘reasonable / polynomial time’.
72
How is data stored on and read from a magnetic HDD (ADDITIONAL BONUS POINTS)
Learn 2 points.
*Whole block read together
*Data stored in buffer while being
read
*Can be many disks inside drive
known as platters
*Disk and drive are a sealed unit
*Data near outside edge of disk
stored less densely
*Disk has constant angular velocity
* Files stored in hierarchical structure / directories
* Free / used space indicated in file
allocation table
* Mirroring / striping / RAID may be
used for automatic backup
73
Problems that can occur with databases that are **not** fully normalised
Give 3 points.
Any 3 from:
* Redundant data may waste storage space
* If data is stored more than once then it could be inconsistent
* If data is stored more than once then each copy of the data would need to be updated if it changed
* It might not be possible to store data about one type of entity without creating a record for another type of entity
* When a record for one type of entity is deleted it might delete the data about another type of entity
* May be difficult to select/edit data if it is not atomic
74
What is the difference between physical vs logical topology?
**Physical**: The physical layout of the connections between computers on the network
**Logical**: How the packets flow around a network
