Secondary Storage

• There are 2 main tiers of storage
• Primary storage refers to the memory areas that the CPU can access very quickly, like CPU registers, cache, ROM and RAM
• Primary storage has the fastest read/write speeds and is mostly volatile
• Secondary storage is non-volatile - it's where all the data (OS, applications and files) are stored when not in use
• Secondary storage includes magnetic hard disk drives, solid state drives, CDs and SD cards
• In secondary storage read/write speeds are much slower compared to primary storage
• Hard disks are high-capacity, reliable storage
• Hard disk drives (HDDs) are the traditional internal storage in PCs and laptops - they are often called hard drives
• A hard disk drive is made up of a stack of magnetised metal disks that spin thousands of times a second
• Data is stored magnetically in small areas on the disk's circular tracks
• A movable arm can access these areas and read or write data
• Portable HDDs are popular for backing up and transporting large amounts of data
• Despite their moving parts, HDDs are generally very long lasting and reliable, although they could be damaged by large impacts like being dropped
• Solid state drives are fast and reliable secondary storage
• Solid state drives (SSDs) are storage devices with no moving parts
• SSDs are used for the same purpose as HDDs - for internal/external storage
• Most SSDs use a type of flash memory (a common type of non-volatile memory)
• SSDs have significantly faster read/write times than HDDs
• Using a SSD rather than traditional HDD can give much quicker times for booting up and opening programs and files
• Hybrid drives exist which use solid state storage for the OS and programs, and a hard disk for data
• Like HDDs, potable SSDs can be used to back up and transport data
• USB pen drives and memory cards (e.g. SD cards) are also flash-based, solid-state storage. They're much slower than SSDs and have a much shorter read/write life
• USB pens and memory cards are used to expand the storage capacity of small devices like cameras, smartphones and tablets (which are too small for SSDs or HDDs). Their capacity is very high relative to their small size
• Pros - HDDs are cheaper
• Pros - Both are high capacity but HDDs are higher
• Pros - HDDs have a longer read/write life than SSDs - SSDs can only be written a certain number of times before they begin to deteriorate
• Pros - SSDs are faster
• Pros - SSDs don't need defragmenting
• Pros - SSDs are more shock-proof than HHDs
• Pros - HDDs make some noise, SSDs are silent
• Storage media refers to the actual thing that holds the dta e.g. optical discs
• A storage device is the thing that reads/writes data to media e.g. HDDs
• Optical discs are cheap and robust secondary storage
• Optical discs are things like CDs, DVDs and Blu-ray discs
• CDs can hold around 700 MB of data, DVDs can hold around 4.7 GB and Blu-ray can hold around 25 GB
• This is an optical disc

  
• Optical discs come in 3 forms:

  • Read-only (e.g CD-ROM / DVD-ROM / BD-ROM)
  • Write-once (e.g CD-R / DVD-R / BD-R)
  • Rewritable (e.g CD-RW / DVD-RW /BD-RW)
• Nowadays, the use of optical discs is declining
• As internet speeds increased, straming and download services like Netflix, Spotify and Steam have removed the need for optical discs
• Modern devices like phones and tablets don't have optical drives