![]() No motion, no changing magnetic fields, no voltage induced in the read head, no data. Similarly, the head must be moving relative to the platter to read data, just like a tape recorder. ![]() Hard drive heads float on a small cushion of air created by the spinning disc, and would immediately crash if the arm was not retracted before the drive spun down (handled automatically in all modern drives). Indeed, even the action of reading what's directly under the drive head requires the disc to spin. To view another part of the disc (such as the next sector not under the head) the disc must rotate. Basically, one thin line across the disc is visible to the head. Most drives have a head that can only move along a fixed track across the radius of the disc. For server applications they're usually spinning 24/7. Most modern (roughly from the mid-90s) drives can spin up and down in a few seconds, and the operating system may place the drive into power saving mode after just a few minutes, particularly in laptops. So why would you want to turn them off? You don't turn computers like that off.Įventually, drives got slower (in terms of max RPM) and smaller (in terms of platter size) such that it is feasible to spin them up and down in just a few seconds. The first hard drives were attached to very large mainframe computers, they were always on (or being repaired) and doing work, usually accessing the drives. It may have had some inertia by tradition/norms, too. Do you want to wait 25 seconds every time you go to access the hard disk? It could take many seconds, even a few minutes, for a really big cylinder to get up to many thousands of RPM. Stopping and starting a motor, especially going from zero to really high RPMs very quickly, can impose higher wear-and-tear on the mechanisms than simply leaving it running at a constant speed.Īlso along those lines, older hard disks had physically larger platters than modern drives. Traditionally, the spindle comes up to speed and stays at speed while the computer is on. Such disks are, however, relatively useless in a computer - there's a video on YouTube by Phil's Computer Lab that clearly shows this is not a good idea. There are (were, now obsoleted by flash media), in fact, mechanical hard disks that do not stay running all the time: The IBM Microdrives and other CF-Card-sized storage media typically spin down after about 5-10 seconds (and need about the same time for spin-up and spin-down) - But this was designed-in more because of their intended usage in cameras and other mobile (i.e battery-powered) devices that are not very frequently accessed than to avoid mechanical wear. ![]() This cushion can only be properly maintained when the disk is turning at a very constant speed, that is why during spin-up and spin-down the heads need to be moved out of the way into special landing zones. The second point is that the (minimal) distance between head and disk is actually maintained not by a mechanical, but aerodynamic effect - The heads are in fact flying on a cushion of air rotated by the spinning disk. The drive bearings and the motor are designed for constant operation. Simply spoken, hard disks die when switching on and off, not while running. Yes, mechanical disk drives are constantly spinning, for two reasons:įirst, the wear and tear on the motor and drive is much bigger during spin-up and spin-down than when running at a constant speed. Maybe it's no longer the case, but was it at some point a fact that hard disks spun their discs all the time while powered on? Maybe this is seen as a silly question with an obvious answer, but I'm not sure at all. Surely the motor that spins the disc must only be moving when it needs to move to a different section and it cannot be accessed by the needle moving as much as it can? Maybe it only read the first data needed to boot the OS, and that's what I remember, and after that it settled down when reading from the HDD was less frequent? Why, though? Why cause that kind of wear and tear (and extra noise) at all times? Are, or were in the past, the discs constantly spinning?īecause when you turn on an old computer, you could hear the HDD's motor start and seemingly was spinning the discs as fast as possible, instantly and perpetually. ![]() Now I think I understand everything except one pretty basic thing. Turns out it adds/removes electromechanical charges. I only had a vague understanding that there was (at least) one hard disc and some kind of "needle" that did "something", most likely not etching onto the disc since that would be rather bad for rewriteability. I have to admit that I didn't ever really think about how a hard drive worked until recently. ![]()
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