GCSE OCR Computer Science Paper 1

[1.1] What is the CPU?

The CPU - Central Processing Unit - processes data and instructions, known as the 'brain' of the computer.

[1.1] What is the CU?

The CU - Control Unit - sends signals to control how information passes around the CPU, as well as decoding instructions.

[1.1] What is the ALU?

The ALU - Arithmetic Logic Unit - performs calculations and logical operations.

[1.1] What is the cache?

The cache holds frequently accessed data, as it is faster to access than the main memory.

[1.1] What is computer architecture?

Computer architecture describes how a computer is designed and structured.

[1.1] What is the most common type of computer architecture?

The most common type of computer architecture is Von Neumann.

[1.1] What are registers?

Registers are small units of memory with a specific function.

[1.1]Give the 5 registers.

The 5 registers are:

• PC

• MAR

• MDR

• ACC

• CIR

[1.1] What is the PC?

The PC - Program Counter - holds the address of the next instruction to be fetched from main memory, incrementing on each FDE cycle.

[1.1] What is the MAR?

The MAR - Memory Address Register - holds the address of the instruction to be fetched from main memory.

[1.1] What is the MDR?

The MDR - Memory Data Register - holds data fetched from or to be written to main memory.

[1.1] What is the ACC?

The ACC - Accumulator - holds the results from the ALU.

[1.1] Describe the FDE cycle.

In the FDE cycle:

• The PC address is copied to the MAR and incremented by 1

• The instruction is fetched from the RAM and copied to the MDR

• The instruction is transferred to the CIR and decoded by the CU

• The instruction is executed by the CU through registers

[1.1] What does FDE stand for?

FDE stands for Fetch-Decode-Execute.

[1.2] Give the 3 factors affecting computer performance.

The 3 factors affecting computer performance are:

• Cache memory

• Clock speed

• Cores

[1.2] Explain how cache memory improves performance.

Cache memory improves performance as it is closer to the CPU than the RAM - and therefore allows for data to be accessed more quickly.

[1.2] What is the primary downside of cache memory?

The primary downside of cache memory is that it is expensive, and so most computers have very little of it.

[1.2] What is clock speed?

Clock speed is a measure of how many times the FDE cycle is carried out per second.

[1.2] What is clock speed measured in?

Clock speed is measured in Hz (Hertz), or GHz (Gigahertz) - where 1 GHz is equal to 1 billion instructions per second.

[1.2] Explain how clock speed improves performance.

Clock speed improves performance as more instructions can be carried out per second, and so the computer will generally run faster.

[1.2] What is overclocking?

Overclocking is when a computer's clock speed is increased above the recommended rate.

[1.2] Give one advantage and disadvantage of overclocking.

One advantage of overclocking is that a computer will run faster, but a disadvantage is that it can lead to damage and reduce a machine's lifespan.

[1.2] What is underclocking?

Underclocking is when a computer's clock speed is decreased below the recommended rate.

[1.2] Give one advantage and disadvantage of underclocking?

An advantage of underclocking is that it increases the lifespan of a machine, but a disadvantage is that it will run slower.

[1.2] What is a core?

A core is a complete set of CPU components, acting as another CPU.

[1.2] Explain how cores improve performance.

Cores improve performance as they allow for multitasking, where a CPU can execute multiple instructions simultaneously.

[1.2] What are the 2 limitations of cores?

The 2 limitations of cores are:

• Too many cores can increase latency as they wait for other cores to finish processing

• some software may not run on multi-core computers

[1.3] What is an embedded system?

An embedded system is a computer system built into a larger machine with a specific function.

[2.1] What are the 2 types of storage?

The 2 types of storage are:

• Primary

• Secondary

[2.1] Define volatile and non-volatile storage.

Volatile storage loses all stored data when it loses power, while non-volatile storage is permanent.

[2.1] What is the main advantage of primary storage?

The main advantage of primary storage is that it is faster to access than secondary storage, making it useful for storing programs and data short-term.

[2.1] Give 2 examples of primary storage.

2 examples of primary storage are:

• RAM (Random Access Memory)

• ROM (Read-Only Memory)

[2.1] What is RAM?

RAM is volatile storage that holds data and instructions to be accessed by the CPU.

[2.1] What is ROM?

ROM is non-volatile storage that holds the BIOS (Basic Input Output System), running upon computer startup.

[2.1] Describe the process of virtual memory.

In virtual memory:

• If the RAM has insufficient storage, unused data is transferred to virtual memory in secondary storage

• This allows for data in use to be accessed quickly by the CPU

• When the data in virtual memory is required again, it is swapped with more unused data in the RAM

[2.2] What is the main advantage of secondary storage?

The main advantage of secondary storage is that it is non-volatile, meaning it can store data and programs even when a computer is switched off.

[2.2] Give the 6 characteristics of secondary storage.

The 6 characteristics of secondary storage are:

• Capacity

• Durability

• Portability

• Access speed

• Cost

• Reliability

[2.2] What are the 3 types of secondary storage?

The 3 types of secondary storage are:

• Magnetic

• Optical

• Solid state

[2.2] Describe the 6 characteristics of magnetic storage.

In magnetic storage:

• High capacity

• High reliability

• Low durability

• Low portability

• Low access speed

• Low cost

[2.2] Describe how magnetic storage works.

Magnetic storage works through a disk platter, accessed by a read/write head above.

[2.2] Describe how optical storage works.

Optical storage works through a laser being projected onto a spinning disc.

[2.2] Describe the 6 characteristics of optical storage.

In optical storage:

• Low capacity

• Low durability

• Low access speed

• Low access speed

• Low reliability

• High portability

[2.2] Describe the 6 characteristics of solid state storage.

In solid state storage:

• High capacity

• High durability

• High portability

• High access speed

• High reliability

• High cost

[2.3] What is binary?

Binary is a number system consisting of only 0s and 1s (base 2), used by computers.

[2.3] Why do computers use binary?

Computers use binary as they are made up of transistors - switches with only 2 values - and so they can only represent binary.

[2.3] Give the first 8 units of binary and their values in relation to the previous unit.

The first 8 units of binary are:

• Bit

• Nibble (4 bits)

• Byte (2 nibbles)

• Kilobyte (1,000 bytes)

• Megabyte (1,000 kilobytes)

• Gigabyte (1,000 megabytes)

• Terabyte (1,000 gigabytes)

• Petabyte (1,000 terabytes)

[2.4] What is denary?

Denary (also known as decimal) is a number system consisting of 10 different values (base 10), used by humans.

[2.4] Describe how to convert from denary to binary.

To convert from denary to binary:

[2.4] What is hexadecimal?

Hexadecimal is a number system consisting of 16 different values (base 16), used as a shortened version of binary.

[2.4] Give the letters that represent double digit numbers in hexadecimal.

In hexadecimal, double digit numbers are represented by:

• 10, A

• 11, B

• 12, C

• 13, D

• 14, E

• 15, F

[2.4] Describe how to convert from hexadecimal to binary.

To convert from hexadecimal to binary:

• Write out the binary equivalent for each hexadecimal digit

• Place the values together, giving the complete binary value

[2.4] Describe how to convert from binary to hexadecimal.

To convert from binary to hexadecimal:

• Convert each nibble to its hexadecimal equivalent

• Place the values together, giving the hexadecimal value

[2.4] How are denary and hexadecimal converted between?

Denary and hexadecimal are converted between by first converting to binary, then the other number system.

[2.4] What is binary addition?

Binary addition is a method of adding binary values together without converting to denary first.

[2.4] Describe binary addition.

In binary addition:

• Place one binary value above the other

• Add the digits from right to left using the following rules:

• 0 + 0 = 0

• 1 + 0 = 1

• 1 + 1 = 0 (carry over to next digit)

[2.4] What is an overflow error?

An overflow error is when the result of a binary addition is larger than the number of bits available.

[2.4] What are binary shifts?

Binary shifts are the multiplication and division of binary values.

[2.4] Give the effect of left binary shifts and right binary shifts.

For binary shifts:

• Left = multiplication

• Right = division

[2.4] Give the formula for binary shift effects.

Effect = 2ᴺᵘᵐᵇᵉʳ ᵒᶠ ˢʰᶦᶠᵗˢ

[2.4] Explain how to perform a binary shift.

To perform a binary shift:

• Take the binary value

• Move each digit the specified number of places either left or right

• Any 1s that do not fit cause an overflow error

[2.4] What is a character set?

A character set is a set of letters, numbers and symbols represented by unique binary codes.

[2.4] Give the 2 common character sets.

The 2 common character sets are:

• ASCII

• Unicode

[2.4] How many bytes make up ASCII and how many characters can it represent?

ASCII characters are made up of 1 byte, giving it 256 possible characters to represent.

[2.4] How many bytes make up Unicode and how many characters can it represent?

Unicode characters are made up of 2 bytes, giving it over 65,000 possible characters to represent.

[2.4] Give one advantage of ASCII over Unicode.

One advantage of ASCII over Unicode is that it takes up less storage.

[2.4] Give one advantage of Unicode over ASCII

One advantage of Unicode over ASCII is that it can represent more characters; this allows for many different languages and symbols.

[2.4] Give the formula for text file size.

Text file size = Characters x Bits per character

[2.4] What are the 2 types of image?

Bitmap and vector

[2.4] Describe bitmap images.

Bitmap images are made up of pixels, where each is assigned a binary value to represent the colour.

[2.4] Describe vector images.

Vector images are drawn through mathematical lines and objects.

[2.4] Give one advantage of vector images over bitmap images.

One advantage of vector images over bitmap images is that they can be scaled up without any loss of quality.

[2.4] What is colour depth in images?

Colour depth is the number of bits used in each pixel of an image to represent colour.

[2.4] Give the formula for image file size.

Image file size = Resolution x Colour depth

[2.4] Give the formula for image resolution.

Image resolution = Height x Width

[2.4] Define metadata.

Metadata is additional information about a file that is not a part of the file itself.

[2.4] How is analogue sound recorded and stored digitally?

Analogue sound is recorded by taking the amplitude of the sound wave at intervals - known as samples - and converted to binary.

[2.4] What is bit depth in sound?

Bit depth is the number of bits used to represent each sample of a sound wave.

[2.4] What is sample rate in sound?

Sample rate is the number of times a sound wave amplitude is recorded, measured in Hz (Hertz) or kHz (Kilohertz).

[2.4] Give the formula for sound file size.

Sound file size = Sample rate x Bit depth x Duration

[2.5] What is compression?

Compression is the reduction of a file size.

[2.5] What is the advantage of compression?

The advantage of compression is that it reduces the size of a file, allowing it to be accessed, sent and stored more easily.

[2.5] Give the 2 types of compression.

The 2 types of compression are:

• Lossy

• Lossless

[2.5] Describe lossy compression.

In lossy compression, large amounts of data are permanently removed (noticeable).

[2.5] Describe lossless compression.

In lossless compression, small amounts of data are impermanently removed (unnoticeable).

[2.5] Give one advantage of lossy compression over lossless.

One advantage of lossy compression over lossless is that the file size is reduced more, so it takes up less storage.

[2.5] Give one advantage of lossless compression over lossy.

One advantage of lossless compression over lossy is that it is reversible, so no data is permanently lost.

[2.5] Why can lossless compression be used on a text file, but not lossy?

Lossless compression can be used on a text file to remove unneeded data, but lossy cannot as there is nothing to remove except text.

[3.1] What is a network?

A network is a collection of computers connected together, allowing for communication.

[3.1] What are the 2 types of networks?

The 2 types of networks are:

• Local area network (LAN)

• Wide area network (WAN)

[3.1] What is a LAN?

A local area network (LAN) is a collection of computers across a small geographical area.

[3.1] What is a client-server network?

A client-server network is one where clients are connected to and dependant on a central server, which handles requests and responses.

[3.1] What is a WAN?

A wide area network (WAN) is a collection of computers across a large geographical area.

[3.1] What is a peer-to-peer network?

A peer-to-peer network is one in which clients are connected to each other without the need for a central server.

[3.1] What is a network topology?

A network topology refers to how computers are laid out on a local network.

[3.1] Give 2 types of network topology.

2 types of network topology are:

• Star

• Mesh

[3.1] Describe a star topology.

In a star topology, computers are connected to a central device (such as a switch), which directs traffic to other computers.

[3.1] What are the 2 types of mesh topology?

A mesh topology can either be a full mesh or partial mesh.

[3.1] What is the difference between the 2 mesh topologies?

In a full mesh topology, every computer is connected to every other computer; meanwhile in a partial mesh, every computer is connected to only some other computers.

[3.1] What is data broken down into when transferred across networks?

When data is transferred across networks, it is broken down into data packets.

[3.1] Give and describe the 3 sections of a data packet.

The 3 sections of a data packet are:

• Header, addresses and packet number

• Payload, actual data

• Trailer, checksum to ensure no corruption has occurred