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Oct 1, 2011

Hard Disks: Reviews

Nearly every desktop computer and server in use today contains one or more hard-disk drives. Every mainframe and supercomputer is normally connected to hundreds of them. You can even find VCR-type devices and camcorders that use hard disks instead of tape. These billions of hard disks do one thing well -- they store changing digital information in a relatively permanent form. They give computers the ability to remember things when the power goes out.
In this article, we'll take apart a hard disk so that you can see what's inside, and also discuss how they
organize the gigabytes of information they hold in files!!!

A typical desktop machine will have a hard disk with a capacity of between 160 and 500 gigabytes. Data is stored onto the disk in the form of files. A file is simply a named collection of bytes. The bytes might be the ASCII codes for the characters of a text file, or they could be the instructions of a software application for the computer to execute, or they could be the records of a data base, or they could be the pixel colors for a GIF image. No matter what it contains, however, a file is simply a string of bytes. When a program running on the computer requests a file, the hard disk retrieves its bytes and sends them to the CPU one at a time.
There are two ways to measure the performance of a hard disk:
  • Data rate - The data rate is the number of bytes per second that the drive can deliver to the CPU. Rates between 5 and 40 megabytes per second are common.
  • Seek time - The seek time is the amount of time between when the CPU requests a file and when the first byte of the file is sent to the CPU. Times between 10 and 20 milliseconds are common.
The other important parameter is the capacity of the drive, which is the number of bytes it can hold...!!


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