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| A secondary storage device that has spinning platters and a movable arm assembly. Organized as cylinders, tracks, and sectors. |
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| A single disk in the magnetic disk. |
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| Moves forward and backward to read information from a platter. |
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| The surface of a platter is logically divided into circular tracks, which are then divided into sectors. |
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| The set of tracks that are at one arm position. |
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| The speed at which data is transferred between the drive and the computer. |
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| The time it takes to move the arm to the desired cylinder. |
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| The time for the desired sector to rotate to the disk head. |
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| Carries out commands from the host controller to read or write data from or to the disk. |
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| Sometimes used for backups, due to large size but slow access time. |
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| Smallest unit of transfer. Modern disk drives are addressed as large one-dimensional arrays of these. |
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| Locally attached storage. |
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| Storage attached through a network. |
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| A private network made using storage protocols rather than networking protocols that connects servers and storage units. Very flexible. |
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| Scheduling how requests for a disk are completed. |
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| The requests are serviced in the order they arrive in. |
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| The shortest seek time of all requests is done first. Not possible since it requires knowledge of future. Also not optimal. |
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| Starts at one end of the disk and moves to the other end, servicing requests along the way, then doing it again on the way back. |
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Definition
| Like SCAN scheduling but on its way back it ignores all requests to prevent preferential treatment toward the middle of the disk. |
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| Like scan but doesn't go all the way to the end, just goes to the last request in that direction. |
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| Look scheduling plus circular behavior. |
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| Changing the logical block size. |
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| When the disk undergoes low-level formatting some of the sectors are made not visible to the operating system. These are used to the replace any bad blocks found. |
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Definition
| When a bad block is found, data is transferred to an adjacent free block and then data is transferred to the now free block. This is repeated until all the blocks from the bad block to the replacement block have been shifted and then the bad block is mapped to the next free block which is now right next to it. Prevents bad blocks from reducing the effectiveness of disk scheduling algorithms. |
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Definition
| Redundant array of independent disks. Having many disks operate in parallel to increase reliability and speed. |
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| How long it takes on average for a disk to fail. |
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| How long it takes for data loss to occur. |
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| Storing the same data in multiple places. |
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| Duplicating disks to improve reliability. Very simple but also expensive. |
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| Improving disk performance by splitting data across multiple disks. |
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| The bits of each byte are split across multiple drives. |
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| The data is stripped by block. |
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Definition
| A disk not used for data but is configured to be used as a replacement should any other disk fail. Used to automate disk replacement. |
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