OCR Computer Science GCSE 1.2 - Memory and Storage

Why do computers have primary storage (memory)?

To provide fast access to data, instructions and software currently in use by the CPU.

What does primary storage usually consist of?

RAM and ROM.

What does it mean for memory to be volatile?

Its contents are lost when the computer loses power.

What is stored in the Random Access Memory (RAM)?

The data and instructions that the computer is currently working with.

Is the Random Access Memory (RAM) volatile or non-volatile?

Volatile.

What is stored in the Read-Only Memory (ROM)?

Firmware that is essential for the computer to boot up and operate.

True or false: the ROM's contents can be modified during normal operation.

False.

Is the Read-Only Memory (ROM) volatile or non-volatile?

Non-volatile.

Why might virtual memory be needed in a system?

When a computer's RAM is full and there are still more programs or data that need to be loaded.

How does virtual memory work?

The system uses part of the secondary storage (such as a hard drive or SSD) as if it were extra RAM.

What is stored in the cache?

Frequently used data and instructions.

Name three types of secondary storage.

Solid-state, optical, and magnetic.

How do Solid State Drives (SSDs) store data?

Using electrical circuits (with no moving parts) that trap an electrical charge.

How do optical disks store data?

In a form such as a CD or DVD that can be read optically by a laser.

How do magnetic hard disks store data?

Using many, tiny magnetised regions.

Rank the three secondary storage types from highest to lowest capacity.

Hard-disk drive, solid-state drive, optical disk.

Rank the three secondary storage types from highest to lowest speed.

Solid-state drive, hard-disk drive, optical disk.

Rank the three secondary storage types from best to worst portability.

Solid-state drive, optical disk, hard-disk drive.

Rank the three secondary storage types from most to least durable.

Solid-state drive, hard-disk drive, optical disk.

Rank the three secondary storage types from most to least reliable.

Solid-state drive, hard-disk drive, optical disk.

Rank the three secondary storage types from cheapest to most expensive per GB.

Hard-disk drive, optical disk, solid-state drive.

Give two use cases for hard-disk drives.

Desktop PCs and servers.

Give three use cases for solid-state drives.

Laptops, phones and tablets.

Give a use case for optical disks.

Sharing and distributing small volumes of data.

Why must data in computer systems be stored in binary format?

Because it has only two states (0 and 1) which map directly to on/off states of electronic components.

List the units of data storage with their relative sizes.

Bit, Nibble (4 bits), Byte (8 bits), Kilobyte, Megabyte, Gigabyte, Terabyte, Petabyte.

What is the fundamental unit of information?

A bit.

What does "bit" stand for?

Binary digit.

How many bits are in a byte?

8.

What is the symbol for a bit?

b.

What is the symbol for a byte?

B.

What is a kilobyte (kB) equal to?

1,000 bytes.

What is a megabyte (MB) equal to?

1,000 kilobytes.

What is a gigabyte (GB) equal to?

1,000 megabytes.

What is a terabyte (TB) equal to?

1,000 gigabytes.

What is a petabyte (PB) equal to?

1,000 terabytes.

What is the correct order of units from smallest to largest?

Bit → Byte → Kilobyte → Megabyte → Gigabyte → Terabyte → Petabyte.

What is the difference between b and B?

b = bit, B = byte.

How many bytes are there in 3 MB?

3,000,000 bytes.

How do you convert denary to binary?

Use place values (powers of two), subtract values, place 1s and 0s until the number reaches 0.

What is the 8-bit binary equivalent of the denary number 13?

00001101.

How do you convert binary to denary?

Add together the place values where there is a 1.

What is the denary equivalent of the binary number 1010?

10.

How do you convert binary to hexadecimal?

Split into two 4-bit nibbles, convert each to denary, then to hex.

What is the hexadecimal equivalent of the binary number 11011111?

DF.

How do you convert hexadecimal to binary?

Convert each hex digit to a 4-bit binary nibble.

What is the binary equivalent of the hexadecimal number A7?

10100111.

How do you convert denary to hexadecimal?

Convert denary to binary, then binary to hexadecimal.

What is the hexadecimal equivalent of the denary number 254?

FE.

How do you convert hexadecimal to denary?

Convert hex to binary, then binary to denary.

What is the denary equivalent of the hexadecimal number 2F?

47.

What is the binary value of hex F?

1111.

What is the result of 0 + 0 in binary?

0.

What is the result of 1 + 0 in binary?

1 (carry 0).

What is the result of 1 + 1 in binary?

0 (carry 1).

What is the result of 1 + 1 + 1 in binary?

1 (carry 1).

What is a binary shift?

Moving the bits of a binary number left or right.

What does a left binary shift do?

Multiplies the number by 2 for each shift.

Which side are 0s added to in a left binary shift?

The right.

What does a right binary shift do?

Divides the number by 2 for each shift.

Which side are 0s added to in a right binary shift?

The left.

Shift 00101100 left by 1. What is the result?

01011000.

Define most significant bit.

The bit with the highest value.

How can you identify the most significant bit?

The leftmost 1 in the binary number.

Define least significant bit.

The bit with the lowest value.

How can you identify the least significant bit?

The rightmost bit in the binary number.

True or false: adding additional 0s to the left of a binary number changes its value.

False.

What is character encoding?

Converting characters into binary codes.

Why is character encoding necessary?

Computers can only process binary data.

What is a character set?

A collection of characters and their binary codes.

Name two character sets.

ASCII and Unicode.

ASCII 'A' is coded as 65. What is ASCII 'E'?

69.

State the equation to calculate text file size.

Bits per character × number of characters.

What is a pixel?

A single picture element.

How are images represented in a computer?

As pixels with colour values stored in binary.

What is image metadata?

Data about an image (format, resolution, colour depth).

What is colour depth?

The number of bits used per pixel.

How many colours can 1-bit colour depth represent?

2.

How many colours can 8-bit colour depth represent?

256.

What happens to file size if colour depth increases?

File size increases.

What happens to image quality if colour depth increases?

Image quality improves.

What is resolution?

The number of pixels in an image (width × height).

State the equation to calculate image file size.

Colour depth × width × height.

How is sound represented in a computer?

By sampling an analogue wave.

What is the sample rate?

The number of samples taken per second.

What is sound bit depth?

The number of bits per sample.

What happens when sample rate increases?

Better quality, larger file size.

What happens when bit depth increases?

More accurate sound, larger file size.

State the equation to calculate sound file size.

Sample rate × duration × bit depth.

What is data compression?

Reducing file size with little or no data loss.

Why is data compression used?

Save storage, speed up transfer, reduce bandwidth.

What are the two main types of compression?

Lossy and lossless.

What is lossy compression?

Removes some data permanently.

Is lossy compression reversible?

No.

What is lossless compression?

All data preserved.

What is a benefit of lossy compression?

Smaller file sizes.

What is a drawback of lossy compression?

Loss of quality.

What is a benefit of lossless compression?

No data loss.

What is a drawback of lossless compression?

Larger file sizes.

Which compression type is best for text or code?

Lossless.