Computing GCSE: Primary and Secondary Storage

• The Need for Primary Storage

  • Computer systems need both primary and secondary storage to operate
  • Both types of storage play a crucial role in the operation of a computer system
• Primary - Volatile (except ROM) & Small capacity
• Secondary - Non-volatile & Large capacity
• Primary storage

  The fast, short-term, working memory that is directly connected to the CPU, such as RAM, Cache, and Registers
• • The Fetch-Execute Cycle is the cycle that the central processing unit (CPU) runs through billions of times per second to make a computer work
• • A computer needs primary storage because access times are considerably faster than secondary
• With primary storage, the time taken to complete operations such as the Fetch-Execute Cycle is dramatically reduced 
• • Primary storage holds the data and instructions that the CPU needs to access whilst the computer is turned on
• Primary storage is used as short term, working memory, in hardware that is directly connected to the CPU
• Registers are small amounts of very fast memory built into the CPU itself
• Cache Memory is an area of high speed RAM which sits between the registers and main memory
• RAM is commonly purchased in 16 or 32 gigabytes whereas secondary storage such as a hard drive is in terabytes
• • Performance of primary storage means a much higher cost which limits the amount that is used
• • RAM (Random Access Memory) is primary storage that is directly connected to the CPU and holds the data and instructions that are currently in use
• • RAM is volatile which means the contents of RAM are lost when the power is turned off
• • For the CPU to access the data and instructions they must be copied from secondary storage
• • RAM is very fast working memory, much faster than secondary storage
• • RAM is read/write which means data can be read from and written to
• • In comparison to ROM, RAM has a much larger capacity
• • ROM (Read Only Memory) is primary storage that holds the first instructions a computer needs to start up (Bootstrap)
• • ROM contains the BIOS (Basic Input Output System)
• • ROM is a small memory chip located on the computers motherboard
• • ROM is fast memory, much faster than secondary storage but slower than RAM
• • ROM is non-volatile which means the contents of ROM are not lost when the power is turned off
• • ROM is read only which means data can only be read from
• • In comparison to RAM, ROM has a much smaller capacity
• • Virtual memory is an extension of primary storage (RAM) located on secondary storage
• The operating system uses virtual memory as if it were part of RAM
• • In situations where RAM is close to being full, virtual memory can be used so that the computer remains operational
• • Programs and data not currently being executed are transferred to virtual memory
• • From virtual memory, programs and data are transferred back to RAM when they are needed
• • Virtual memory is much slower than RAM and it's use will impact negatively on system performance.
  • To avoid the use of virtual memory, increase the size of the RAM
• • A computer needs secondary storage for long term storage of programs and data that are currently not in use 
• • Secondary storage is needed as ROM is read only and RAM is volatile
• • Secondary storage holds the programs and data whilst the computer is turned off (non-volatile)
• • Performance of secondary storage is slower than primary storage but capacity is much higher which makes it perfect for backup & archive of data files
• What are the characteristics of secondary storage?

  • Capacity What is the maximum amount of data that can be stored?
  • Speed How fast can data be read from and written to? (R/W)
  • Cost How much does it cost?
  • Portability How easy is it to move around? What is the physical size? Weight?
  • Durability How robust is the storage?
  • Reliability What is the probability that the device will consistently perform its function?
• • Storage devices are non-volatile secondary storage, that retain digital data within a computer system
  • They provide a means of storing, accessing, and retrieving data, which can include software applications, documents, images, videos, and more
  • There are 3 types of storage:
  • Magnetic
  • Solid State
  • Optical
• • Magnetic storage is a type of non-volatile media that uses magnets (polarity) to store binary 0s and 1s
• • Magnetic storage is a type of non-volatile media that uses magnets (polarity) to store binary 0s and 1s