Memory, Storage Devices & Media

• Primary Storage VS Secondary Storage

  • The CPU directly accesses primary storage
  • The CPU does not directly access secondary storage
• Random Access Memory (RAM) (Primary)

  • Used by a system when it needs to store and access data that is actively being used or processed by the user immediately.
  • Features of RAM
  • Volatile/temporary memory (contents lost if RAM is turned off)
  • Used to store data, files
  • It can be written to or read from, and the contents of the memory can be changed
  • The larger the size of the RAM, the faster the computer will operate
  • RAM never runs out of memory and continues to run slow
  • As RAM becomes full, the processor has to access the continually hard drive to overwrite old data on RAM with new data
• RAM is of two types:

  • DRAM (Dynamic RAM):
  • consists of a number of transistors and capacitors
  • need to be constantly refreshed
  • less expensive to manufacture
  • higher memory capacity
  • main memory is constructed
  • consumes less power
  • SRAM (Static RAM):
  • uses flip flops to hold each bit of memory
  • doesn't need to be constantly refreshed
  • has a faster data access time
  • CPU memory cache makes use of SRAM
• Virtual memory (Primary)

  • When RAM runs out of memory, there is a problem with memory management; thus, the system has a high chance of crashing. This is why virtual memory comes into the picture.
  • The virtual memory can be either HDD or SSD
• Advantages of virtual memory:

  • Can be larger than the physical memory provided in the RAM.
  • Avoids the need to install/upgrade RAM, as it could be expensive
  • The system wastes no storage on unwanted/unused data.
• Read Only Memory (ROM) (Primary):

  • Features of ROM
  • Non-volatile/permanent memories (contents remain even when ROM is turned off)
  • Used to store start-up instructions (basic input/output systems)
  • Data/contents of a ROM chip can only be read and cannot be changed
• Hard Disk Drives (HDD) (Secondary)

  • Data is stored in a digital format on the magnetic surface of the disks (platter)
  • A number of read/write heads can access all of the surfaces of the disk
  • Each platter will have two surfaces which can be used to store the data
  • Data is stored on the surfaces in sectors and tracks
  • HDD has very slow data access compared to RAM
• Solid-State Drive (SSD) (Secondary)

  • There are no moving parts, and all data is received at the same time (not like HDD)
  • Store data by controlling the movement of electrons within NAND chips, as 1s and 0s
  • Non-volatile rewritable memory
• Benefits of using SSD rather than HDD:

  • More reliable (no moving parts)
  • Considerably lighter (suitable for laptops)
  • Lower power consumption
  • Run much cooler than HDDs
  • Very thin
  • Data access is faster than HDD
• CD/DVD Disks (Off-line)

  • Laser (red) light is used to read and write data on the surface of the disk.
  • A thin layer of metal alloy is used to store data.
  • Both systems use a single spiral track that runs from the centre of the disk to the edge
  • DVD uses Dual-Layering, which increases the storage capacity (two individual recording layers)
• Blu-ray Disks (Off-line)

  • Uses a blue laser to carry out read-and-write operations
  • The wavelength of laser light is less than CD and DVD (stores up to five times more data than DVD)
  • Automatically come with secure encryption (prevent piracy and copyright infringement)
  • Used as backup systems
• USB Flash Memories (Off-line)

  • Very small, lightweight, and suitable for transferring files
  • Small back-up devices for photo, music
  • Solid state, so needs to be treated with care
• Cloud Storage (Off-line)

  • A method of data storage where data is stored on remote servers
  • The same data is stored on more than one server in case of maintenance or repair, allowing clients to access data at any time (data redundancy)
• 3 types of cloud storage:

  • Public cloud storage - client and provider are different companies.
  • Private cloud storage - client and provider integrated and operate as a single entity
  • Hybrid cloud storage - a mix of both public and private cloud.
• Advantages of cloud storage:

  • Data can be accessed anywhere, anytime with internet access
  • Users do not need to carry external drives or use the same machine to access the data
  • Provides backup to allow users to recover the data
  • Unlimited storage capacity

  Disadvantages of cloud storage:

  • Unstable or slow internet access => difficult to access the data
  • Requires subscription / payment which can be costly
  • Upload/download large data can be limited by ISP
  • Security is controlled by the cloud provider which users have no control over