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Hard Disk

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Hard Disk The Physical Characteristics of All Disks The hard disk has one or more metal platters coated top and bottom with a magnetic material similar to the coating on a VCR magnetic tape. In the VCR the tape moves by a fixed recording and sensing device (the "head"). In a disk, the recording head is on a movable metal support called the "arm". Information is recorded onto bands of the disk surface that form concentric circles. The circle closest to the outside is much bigger than the circle closest to the center. Since each metal platter has a top and bottom surface, there are at least two magnetic circles for each size and location. However, a disk may have as many as five platters, producing ten of these identical circles at the …show more content…

Some disk models are optimized for this and reduce cost, power use, and heat by limiting seeks performance. This is definitely not the type of disk on which you want to install an operating system. • If the disk moves the arm as fast as it can to the right location, once it gets there it may have to wait for a long latency period while the data rotates around to the arm location. Newer smarter disks can calculate that this is going to occur and respond by using less power to move the arm more slowly into position while still getting there with time to spare. This type of "intelligent seek" saves power and reduces noise without effecting performance. • One company took its Enterprise 15,000 RPM disk hardware and reprogrammed it to run at 10,000 RPM. Then they looked to see what improvements they could get in exchange for the slower speed. Among other things, the amount of data on the disk jumped from 300 to 400G while power use and heat dropped. The conclusion is that while all disks work about the same way, in any given generation of hardware there are opportunities to tweak, optimize, and specialize. Be careful when you purchase a disk intending to get a general purpose system that you aren't buying one of the disks optimized for

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