Hard Disk Drive
A Hard disk drive is a permanent storage device used in a computer system. A Hard Disk Drive or HDD consists of rotating platters of magnetic disks that store large amounts of data in a non-volatile or permanent state. That means that HDD data does not disappear when you turn off the computer.
Hard Disks are slower than main memory but faster than Optical drives. HDDs usually store the operating system and application software of a computer.
HDD capacity is measured in gigabytes or billions of bytes and in terabytes or trillions of bytes. The performance of an HDD is determined by a variety of factors including:
Revolutions Per Minute (RPM): How fast the platters spin per minute. The higher this number the faster a hard disk is. At the time of writing a 7200RPM hard disk would be the standard for desktop computers.
Cache: The amount of cache memory on-board the drive. The cache memory is used to store frequently accessed data. It is faster to deliver data from the cache than from the platters themselves.
Access time: Access time is the amount of time it takes to find and retrieve data from the hard disk. The lower the access time the faster the hard disk functions. Access time of 12-13ms is the norm for desktop hard drives at the time of writing.
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