Secondary Storage

Sam Walsh, EDUC 5033

MAGNETIC STORAGE-Hard Disk Drive (components)

Electric motor spins the hard drive’s disk 7,2000 revs per min. The circuit board keeps the speed constant. The actuator arms that hold the reeds right heads are split and the ends ride the disk platter. Heads never touch the disks. Heads float on a cushion of air created by spinning disk. Arms move to the right and left. Electricity and magnetism make the arms move across the disk at lightning speed.

(data) Is stored in tiny concentric tacks … on the disk’s surface. During manufacture 2000 tracks are created. Each track is divided into sectors that tell the heads exactly where to read. Magnetic film memorizes all the information… 31 billion bits in a square centimeter. 100,000’s full of images are stored, squeezing data into mini bites.


1.2 mm thick polycarbonate plastic with a clear substance with a think layer of aluminum. One spiral that contains on all the data on a particular disk which saves as spirals as a Stores as a series of flat spots or bumps. If we straightened out this spiral it would be 3 ½ miles long. Drive motor that spins the disk, a laser and lens pair which shoots a laser onto a disk, tracking mechanism that moves the laser and the lens that the disk to the outside of the disk at the right time.

Turning physical bumps into actual signals on our computer. It bounces laser beam back onto the disk, if it hits a flat reflective surface, it reflects that sensor back toward a sensor that picks up a signal…but instead it hits a bump….it won’t be able to pick up a signal. Then we take digital signal and put it into digital analog converter, which figures out how frequent these bumps are which give us our analog, signal and then we can increase intensity of our voltage and put into a speaker.

Two methods: encryption or non-sequential data ordering.

Writing Data to a Disk

Invented a clear dye that when heated up became opaque. Heats up a clear dye to become non-clear.

How Re-Writeable disks work

If you heated up a dye to a temperature it would clear when cooled. At different temp it would cool down and become opaque. Reflective or non-reflective.

What makes a DVD work?

CD is made up of layers. Injection molded clear polycarbonate plastic that is engraved with a series of bumps before adding a clear acrylic before adding a label. Computer reads the engagements at the center of the cd then going out. Light from the laser hits the spiral and depending on whether it strikes a bump or a flat, reflects off the surface in a different direction, the computer either reads these as a 1 or a 0.


Solid Straight Drive. Rewrite just a small portion of the time. Building file systems on top of flash. Oxide layer Stores electrons. Charge that layer it fills up with electrons. Advantages over a disk. Non-volatile. It works for a long time, Solid State(No big moving parts and is quiet) Writing times very but. faster than a disk. Cost is more.

Comment Stream