Hardware Storage Devices
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Secondary storage devices
Hard disk Optical disk Solid state disk
DRUM memory
Read-write heads Stored more data than punch cards Few Kb
Core memory
• no moving parts • quicker • made by hand
Floppy disk
• portable • small • 8 inch = 80Kb
What are hard disks made of
• hard metallic material • hermetically sealed • several in a stack • counted with thin magnetic film • changes in the direction of magnetism representing 0s and 1s
How are hard disks organised
Into concentric tracks Each track is split into sectors Sectors can be individually addressed by the OS
Examples of optical disks
CD DVD Blu-Ray
How are optical disks read and written to
Laser technology
How are optical disks organised
One single spiral track - starts in the middle
What are optical disks made of
Land and pits as 0s and 1s Protective layer to prevent data corruption Writeable disks are coated in a photosensitive dye
Why can you fit more data on Blu-Rays
Because blue light has slower wavelength
SSD facts
• non-volatile • NAND memory
How are SSDs organised
Into blocks Blocks managed by a controller
What are SSDs made of
Semiconductors Floating gate transistors Control gate transistors Layer of oxide
Floating gate transistors (FGT)
Trap and store charge
Control gate transistors (CGT)
Reads and writes to data to FGT
Layer of oxide
Is between two transistors trapping charge in FGT