1.2 Memory & Storage

• What does Primary memory do?

  Memory holds data, programs and instructions
• What is Primary memory?

  Primary memory is read-write giving the processor fast access to the data and instructions that the primary memory holds

  (Primary memory is built inside the computer)
• What are the types of Primany memory?

  Read-only memory (ROM) and Random access memory (RAM)
• What is the difference between Primany and Secondary memory?

  Primary memory has limited memory compared to secondary storage
• What is ROM and what is it made of?

  - ROM is non-volatile, read-only and is ideal for storing instructions and data

  - ROM is often made of flash memory so the contents cannot be changed easily
• What is an example of a program stored in ROM?


  The Basic Input Output System (BIOS)
• What does the The Basic Input Output System (BIOS) do?

  It loads the computer operating system from the hard drive to the RAM and checks the system for errors
• What can RAM do?

  - store and access data from any location

  - be changed at any time by overwriting it

  - hold more data than ROM

  - hold data and programs simultaneously

  - be upgraded easily
• Compare the speed and price of RAM and ROM.

  RAM is more expensive and faster
• What is Virtural memory?

  Virtual Memory is the use of secondary storage as additional primary memory when there's no more space in the RAM
• When is Virtural memory used?

  When there's not enough primary data secondary storage is used to store data temporarily
• What happens of the CPU needs to read data in Virtural memory?

  If the CPU needs to read data in Virtual Memory it has to be moved back to RAM
• Does Virtural memory make a computer slower or faster and why?

  Virtual Memory makes the computer slower because the processor has to wait for data to be swapped between hard disk and RAM
• Where is Virtural memory?

  Virtual Memory is in the Hard Disk
• Why is Virtural memory used?

  It could be problematic to buy more RAM because it is expensive and we may only need more memory temporarily so instead Virtual Memory is used
• How does Virtural memory work?

  Memory is split into sections called "pages" and virtual memory moves these pages between RAM and secondary storage

  (when a page is moved to the HDD it is put into the "pagefile")
• What is Cache Memory?

  High-speed RAM built into the processor

  (Normally very small)
• Why is Cache memory used?

  Data can be transferred to and from the cache memory quicker than RAM
• What is Cache memory used for?

  Used to temporarily hold data and instructions that the processor is likely to reuse which allows faster processing
• Compare the Price of Cache memory to that of RAM.

  More expensive than RAM
• Compare L1 cache and L2 cache.

  - L1 cache is fast but small, it is normally used to hold the most frequently used data

  - L2 cache is bigger but slower, it is used to hold less used information
• What is Flash memory?

  a kind of memory that retains data in the absence of a power supply.

  (Its external secondary storage)
• What is Flash memory based on?

  Flash memory is based on a technology called Electrically Erasable Programmable Read-Only Memory (EEPROM) which can be used to make all sorts of flash memory devices.
• Describe the speed of Flash memory.


  It is faster than other storage media like HDDs because there are no moving parts
• Describe the lifespan of Flash memory.

  It has a short lifespan and can only be re-written a certain number of times before it degrades
• Properties of flash memory

  - Read-write memory

  - Non-volatile

  - Fast to access but not as fast as RAM
• Examples of Flash Memory.

  - ROM

  - USB memory sticks

  - Solid-State drives
• What is Secondary Storage?

  Non-volatile long-term storage
• Do embedded comuters require secondary stoege?

  Embedded computers don't require secondary storage because they don't need to store data when the power is turned off
• Why is secondary storage needed?

  Needed to keep programs and data indefinitely
• What are the three types of secondary storage?

  - Magnetic storage devices

  - Optical storage devices

  - Solid State storage devices
• How do Magnetic storage devices work?

  It uses magnetic fields to magnetise tiny individual sections of a metal spinning disk called a platter

  - A magnetised section represents a binary "1"

  - A demagnetised section represents a binary "0"
• How to read and write a Magnetic storage device?

  - To write data the head magnetises or demagnetises a section of the disk that is spinning under it

  - To read data the head makes note of whether the section is magnetised or not
• Examples of Magnetic storage devices.

  hard disk drives
• How do Optical storage devices work?

  - uses a laser to scan the surface of a spinning disk

  - there are flat areas known as lands and hollows known as pits

  - the sensor looks for reflected light

  - reflected light means there's a land and it represents the binary "1"

  - no reflection means there's a pit and it represents the binary "0"
• Describe how ROM media is read/written.

  ROM media have data prewritten and it cannot be overwritten (e.g. Music, Films and Software)
• Describe how R media is read/written.


  R media are blank, it can be written once but read many times
• Describe how RW media is read/written.

  RW works are the same as R media but can be written multiple times
• Examples of Optical storage devices.

  CD, DVD, Blu-ray discs
• Examples of Solid State storage devices.

  solid state drives and USB memory sticks