Storage Devices - 3 TYPES

Storage Devices - 3 TYPES

1. 1. Primary Storage - its memory inside a computer. RAM, ROM, Cache

   • 2. Secondary Storage - access by device that is part of a computer - hard disk drive, Solid State Drive
     • 3. Off line Storage - This is memory not permanently connected to a computer - Examples CD,DVD, USB Flash Memory
       • Secondary Offline Storage - Non volatile
         • Non Volatile
           • USes: Programs and data stored on hard disk - CDs may be used to distribute software, music. Memory Sticks may be used to transport data from one place to another. Magnetic take or external hard drives may be used for back up
         • Magnetic Tapes
           • Serial Access Medium - which means it has to be read starting at the begining of the tape. It has a large capacity but is slow to transfer data. It is mainly used for cold storage storing large volumes of data offline which is not accessed much.
           • Data is stored on magnetic surface
             • Data is created by magnetising fine iron particles on the disk
               • HArd drive will have several platters that can spin at many thousand times a second
                 • Normally each platter will have 2 surfaces which can be used to store the data
                   • Disk heads mounted on mechanical arms read and write data
                     • Disks contai concentric circles called tracks
                       • Each track is divided into sectors
           • Magnetic Storage Hard Disk Drive
         • Flash memory
           • Non volatile
             • It has no moving parts
               • It is a type of electronically erasable programmable read only memory
                 • stores data by controlling the movement of electrons
                   • works by flashing an electrical current through a barrier
                     • electrons pass from the soure to the drain, and some are trapped in between on the floating gate
                       • This gate effect continues whether there is no electricity and so sotrage remains when the power is removed
           • Flash versus EEPROM
             • Flash - Uses NAND chips. Slower than EEPROM. Cheaper, only alows blocks of data to be read or erased. Used when large amounts of stroage are needed/rewritten often
             • EEPROM - Uses NOR chips. Faster than Flash. More expensive. Allows data to be read or erased in single bytes at a time. USed when smaller amounts of sotrage/speed i needed and not rewritten often
           • Flash Memory is widely used in mobile phone, mp3, digital camera
         • Solid State Drive
           • Has no moving parts
             • USes non volatile flash memory
           • Differences between SSD and HDD
             • Price - SSDs are 10 times more expensive than HDDs per MB
               • Power - HDDs use about 3 times more battery power than SSDs
                 • Capacity - SSDs generally have a much smaller capacity than HDDs
                   • Size - SSds are smaller and lighter than HDDs
                     • Speed - SSDs are almost twice as fast at loading up and copying files
                       • Noise - SSDs are silent wheras HDDs make spinning disk sounds
                         • Reliability - Both are highly reliable storage but HDD is more vunerable to knoocks as it has movign parts and HDD has greater longevity for read/write functions
           • CDROM, DVD-Rom
             • Read Only
               • Mass Produced by Pressing
                 • Data Written to them before they are sold
           • DVD-RAM
             • DVD-RAM disks have concentric tracks rathan than one spiral track
               • Allows simultaneous read and write operations - using red laser
                 • Allows Numerous read and write opertions - up to 100,000 times
                   • Greater Longevity wgich makes then ideal for archiving
           • Blue Ray
             • Single Spiral Track
               • A Blue laser is used to carry out read and write operations
                 • Smaller wavelength (405 nanometre) so the 'pits' and 'bumps' can be much smaller
                   • Much larger storage capacity
                     • Blue ray uses a single 1.1 mm thick polycarbonate disk - normal DVDs use a sandwich of two 0.6mm thick disks
                       • Blue ray disks automatically come with a secure encryption system which hep to prevent piracy and copyright infringment
           • Advantages of CD DVD BlueRay
             • Has no moving parts so not sensitive to movement
               • Small, therefore portable
                 • Cheap
                   • Takes up little space physically
             • Suitable Storage Devices - what to consider
               • Capacity
                 • Speed
                   • Portability
                     • Durability
                       • Relaibiltiy
           • Disadvantages of CD DVD BluRay
             • Ted to be smaller capacity
               • Easily Damaged/scratched
                 • Slow wrtie speeds
       • Why use Virtual Memory?
         • Allows more programs and data to be loaded when there is not enough RAM
           • Adding more RAM means more memory for programs and data to be loaded into. CPU can multitask more programs. Programs may run faster due to less use of virtual memory
         • What is Cache Memory
           • A temporary storage area between the CPU and RAM. Stores frequently used instructions and data. Data does not need to be fetched from RAM therefore faster access, Used faster RAM, more expensive
         • Differences between Dynamic RAM and Static RAM
           • Dynamic RAM - Capacitors hold the bits off information (0 and 1). Transistors act as a switch to read/change the capactors valve
             • Needs to be constantly refreshed/charged so values not lost
               • less expensive than SRAM
                 • Higher Storage Capacity than SRAM
           • Static RAM - Use 'flip flops' which hold each bit of memory
             • Low density/less memory per chip
               • Does not need to be constantly refreshed
                 • Much Faster than DRAM
                   • Consumes less power than DRAM
                     • Used when speed is essential e.g. memory cache

2. Differences between RAM and ROM

   • RAM - Random Access Memory
     • Used to Store Data, programme/instructions and any part of the operating systems that are currently in use
       • RAM is volatile - all contents lost when computer is turned off. Easily Expandable. Contents change Frequently
   • ROM - Read Only Memory
     • Stores the boot program/BIOS. USed to boot up the computer when it is switched on. ROM is non volatile. Fixed size for a computer. Contents never change (read only)

3. What happens when RAM is full

   • A section of the hard disk is used to store items in RAM that are currently not being used