Memory & Storage

• What is Random Access Memory (RAM)?

  Volatile, main memory in a computer. When software applications are opened, they are copied from secondary storage to RAM. They stay in RAM until they are closed.
• What does volatile mean?

  All data inside RAM is lost once the computer is turned off because it requires power to operate.
• Data is transferred into RAM from secondary storage for use by the CPU. With more RAM available more data and applications can be stored in it. Because RAM has fast data access times this leads to better performance of the system. A system with more RAM can have more programs open at the same time without any noticeable decrease in performance.
• RAM is slower than cache but faster than secondary storage.
• What is Read-Only Memory (ROM)?

  Non-volatile memory which contains all the instructions a computer needs to properly boot up called the BIOS (Basic Input Output System). When a computer turns on, the CPU reads instructions from ROM such as self-checks and setting up the computer.
• Explain the differences between RAM and ROM.

  RAM is volatile and needs power to maintain the data, ROM is non-volatile and doesn't require power to keep data. RAM is read and write, data can be read from and written to RAM by the computer, ROM is read-only and cannot be changed. RAM holds the operating system and any programs/data currently in use by the computer, ROM holds the data and instructions to start up the computer.
• What is virtual memory?

  Virtual memory is secondary storage used to temporarily store data from RAM. This is needed if there are lots of programs running or if a computer is running complex programs that require extra RAM.
• How can virtual memory affect a computer's performance?

  It creates a delay when transferring data from virtual memory back to RAM as data transfer rates are slower on secondary storage. Virtual memory can make a computer slow to respond when switiching between applications.
• A computer with more RAM will need less virtual memory, reducing the number of data transfers between RAM and secondary storage and therefore delivering improved performance.
• What is magnetic storage?

  Hard disk drives (HDDs) is made up of magnetic disks that magnetically store data. They are used for backing up and transporting large amounts of data. They are very long-lasting and reliable but can be damaged by being dropped.
• What are solid-state drives?

  Solid state drives (SSDs) are faster than HDDs. The SSD has quicker times for botting up and opening programs and files than HDDs because they have no moving parts.
• What are optical discs?

  CD/DVD that store data by reading discs of light.
• Order and compare the different types of secondary storage from lowest - highest.

  Speed: Optical disc, HDD, SSD

  Cost (per GB): Optical disc, HDD, SSD

  Capacity: Optical disc, SSD, HDD

  Durability: CD, HDD, SSD

  Reliability: HDD, CD, SSD
• Why do computers store things in binary?

  A computer is made up of lots of switches. Each switch can be in one of two states: on or off. The two states are represented by the numbers 1 or 0.
• Left binary shift multiples a number. For every place shifted left, the number is doubled. e.g a shift 3 places to right = multipled by 2^3 = 8.
• Right binary shift divides a number. For every placed shifted right, the number is halved. e.g. a number shifted 3 places to the right = 2^3 so it will be divided by 8.
• What is a character set?

  A collection of characters that a computer recognises from their binary representation.
• File size = number of bits per character x number of characters
• Explain the differences between ASCII and Unicode.

  ASCII: Represents 128 characters. Each character has a 7-bit binary code. Can only represent English and numbers.

  Unicode: Uses 16 bits and can store 2^16 characters, over 65000 characters. Can store modern languages and symbols.
• How are images stored in a computer?

  Images are stored using pixel. The colour of each pixel is represented by a binary number. The number of colours available in an image is related to the number of bits the code has.

  With 2 bits 2^2 colours can be stored = 4 colours

  With 3 bits 2^3 colours can be stored = 8 colours etc.
• Colour depth is the number of bits used per pixel. The more bits per pixel, the larger the range of colours in the image. The more colours we have available, the better the representation of the image. The greater the bit depth, the larger the file size.
• Image resolution is the number of pixels in the image. The higher the resolution the more pixels the image is made of so there will be a better quality of the image. This will give a higher-quality image but a greater file size.
• File size(bits) = colour depth x image height x image width
• Metadata is information stored in an image file. This includes:

  . File format

  . Image size

  . Colour depth

  . Resolution
• File size (bits) = sample rate (Hz) x bit depth x length (s)
• Increasing the sample rate will mean there is better quality that will match the original recording better, this will also increases the file size.

  Increasing the bit depth means the file can pick up quieter sounds and will increase the quality of the recording, will also increase the file size.
• Lossy compression- permanently removing data from the file to make it smaller. It cannot return to its original condition.

  Lossless compression- Temporarily removing data to store the file and then restores it to its original state when opened.
• The more RAM in a computer the more programs and data it can run at the same time and the better the computer’s performance.
• Virtual memory is a section of secondary storage used as temporary RAM.
• Any data from a running program that is not currently being used by the computer can be temporarily moved from RAM to virtual memory. When that data is required by the computer, it is moved back from virtual memory into RAM. Moving data between RAM and virtual memory is relatively slow – so using virtual memory slows down the performance of the computer. Adding more RAM reduces the need for virtual memory. If less data is held in virtual memory then there are fewer slow data transfers between RAM and virtual memory. Therefore, adding more RAM improves the performance of the computer.
• What is held in RAM whilst a computer is working?

  Programs currently in use, the operating system and the data from the programs.
• What is virtual memory and how does it work?

  Virtual memory is temporary secondary storage used as extra RAM . Data not in use by the CPU is moved from RAM to virtual memory. If the data needs to be used, it is moved from virtual memory to RAM.
• What is secondary storage and how does it work?

  Secondary storage is extra non-volatile storage for data and programs. Because data in RAM is lost when the computer turns off, secondary storage keeps this data so that it is available next time the computer turns on.
• Which characteristics need to be considered when buying secondary storage?

  Cost

  Reliability

  Speed

  Capacity

  Durability

  Portability
• What is bit depth?

  The number of bits used to store each sample.
• When would lossless compression be used?

  Text files, emails, programs. To ensure nothing important is lost.
• What are benefits of compressing a file before emailing it?

  Reduces file size so it doesn't exceed storage limit. Uses less bandwidth and is sent faster.
• What can not be compressed with lossy compression?

  Text files.
• How is an analogue sound converted to a sound wave?

  A sound wave is sampled and then the amplitude/height is measured. Each sample is measured then stored as a binary number.
• What could be stored as metadata?

  • File size
  • Author
  • File type
  • Bit depth
  • Compression type