Tag: Data Storage

Contributor Post Created with Sketch. Recommended by Ricochet Members Created with Sketch. How to Build a Computer 27: Data Recovery

 

We’ve covered the physical aspects of a hard disk drive, tonight we’ll touch on the way data is organized on the drive, by covering those two most important topics; keeping secrets and ferreting other people’s out.

In this case describing the times this joke has been used since it was last funny.

We’ll start by deleting files: Let’s say that I’ve got a backlog of old and worn-out memes to purge. That’s no problem, you just move them from the exquisitely detailed and organized archive of these things into the trash can, but that doesn’t actually erase anything. Bill Gates, knowing that we mere mortals are flawed and prone to regret, keeps your trashed files around in case your stale jokes may, someday in the future, be called for again. But we’re stronger than that. So we empty the trash folder (or, pro-tip; on a Windows box if you hold down ‘Shift’ as you delete a file the file doesn’t go to the trash at all; it empties automatically.)

Contributor Post Created with Sketch. Recommended by Ricochet Members Created with Sketch. How to Build a Computer 26: Spindles and Platters and So Forth

 

We’ve discussed what it means to actually store information on a hard disk drive, how you magnetize it and how you pull that information off. Neat stuff, but a bit heavy on the abstract physics. Today we’re going to zoom out a bit and look at the mechanical bits of how hard drives work. Here, let me start you off with a picture. Take a look at these two hard drives (conveniently cracked open for viewing purposes), one I borrowed from the boss man, and the other I picked up off the “Free Stuff” shelf when they moved the engineering department. Tell me which you think stores more data:

None of the above. Neither of is ever going to run again. Look at that dust!

Now I’ve actually got no idea on the history of these two drives, what year they were built, their listed capacity. Couple points of difference tell me the one on the left is older, and stores far less information:

Contributor Post Created with Sketch. Recommended by Ricochet Members Created with Sketch. How to Build a Computer 25: The Magnetoresistive Effect

 

Our story starts with Lord Kelvin, one of the great old school physicists. You can read about his career from John Walker’s old Saturday Night Science. Actually, at the point he enters this story I don’t think Kelvin had made lord yet; he was just some bloke named Thompson. This Thompson fellow was playing around with magnets and electricity and that sort of thing. What he discovered is that you can change the resistance of a wire with a magnetic field. And furthermore that that change in resistance depends on the angle between the wire and the magnetic field.

Let’s take that a little more slowly. Change in resistance when you’re in a magnetic field? Okay, I can buy that; there’s all this nonsense about wires and magnets and whatnot that I’ve been blathering about up until this point. Angle? The resistance in your wire will vary a great deal whether it’s parallel or antiparallel to the magnetic field on your disk. (Antiparallel means parallel, but facing the other direction. The northbound lane on a highway is antiparallel to the southbound lane.) If your wire is running current right-to-left and your magnetic field is pointed left-to-right then your wire’s resistance is at it’s highest because of your antiparallel configuration.