Magnetic (External/Internal Hard Drives)

How it works: Read/Write heads on mechanical arm magnetize sections of the surface of the hard drive discs coding positives and negatives. These +/- s are coded as 0s and 1s. Data is stored in the magnetic material. A magnetic read/write head floats just above the surface of the disk.

Cost Per Byte: "On a per-byte basis they are among the cheapest form of storage" (Link to another teach-ict.com article)

Optical Storage (CD's DVD's BlueRay)

How it works: Reading a disc with bumps and flat spots: A disc (CD/DVD) has a reflective layer of metal that has a sequence of bumps and flat spots. Lasers run by motors reflect bumps and flat spots on line of data in different reflective materials and transmit into binary1 or 2 signals.

Reading a disc with various reflective materials: They use dyes in the manufacture of the disc that become opaque with heat from a laser. Once that section of the disc become opaque it does not allow reflection of the laser onto the optical drive having the same effect as the bumps and flat spots.

Writing to a disc: There are various materials used as a layer on the CD that can be marked with the heat of the optical lasers and “burned” in different patterns that the laser can then interpret as binary code.

Cost Per Byte: This was not easy data to find!  Teach-ict.com cost of cd disk memory (CD's cost more per byte of storage than DVD's, hard disks, magnetic tapes, or Flash Drives)

Flash (NAND Flash, SSD, 1.0TB OWC Aura 6G)

How it works: Non moving drive, Stores electrons (even with power off) to code patterns of 0s and 1s. “Cells” can have a neg or pos charge which translates into a 1 or 0 binary code. There is no disc, no arm, no bumps or flat spots, no special layers of material to be read by an optical device. The NAND flash drives are run by electrons in cells. (Like an egg carton with pos or neg charge in each egg spot)

Cost Per Byte:

3. Samsung 850 EVO SSD ($400-450): 1 TB SSD

4. Crucial M550 ($400-450): 1 TB SSD

5. Samsung 850 Pro ($600-650): 1 TB SSD

6. SanDisk Ultra II ($350-400): 960 GB SSD

And more interesting info from Wiki.....As of 2015, the primary competing technology for secondary storage is flash memory in the form of solid-state drives (SSDs). HDDs are the dominant medium for secondary storage due to advantages in price per unit of storage and recording capacity.[5][6] However, SSDs are replacing HDDs where speed, power consumption and durability are more important considerations.[7]

http://en.wikipedia.org/wiki/Hard_disk_drive

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