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Definition
| Provide the bulk of secondary storage for modern computer systems. |
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Definition
| Circular Disk on which data is read. |
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| Moves all read-write heads as a unit. |
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Definition
| Logical division within platters. |
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Definition
| Logical division of tracks. |
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Definition
| Set of tracks that are at one arm position |
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Definition
| The rate at which data flows between the drive and the computer. |
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| Positioning Time (Random-Access Time) |
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Definition
| The time necessary to move the disk arm to the desired clinder and the time necessary for the desired sector to rotate to the disk head. |
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Definition
| The time necessary for the desired sector to rotate to the disk head. |
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Definition
| Time necessary for the desired sector to rotate to the disk head. |
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Definition
| When the head comes in contact with a disk platter. |
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Definition
| Connects the CPU to all other components, except RAM. |
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Definition
| Special electronic processors which carry out data transfers on the bus. |
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Definition
| The controller at the computer end of the bus. |
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Definition
| Built into each disk drive. Controls a hard-disk drive. |
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Definition
| Early secondary-storage medium. Used mainly for backup, and data transfer from one system to another. |
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Definition
| Smallest unit of data transfer. Usually 512 bytes. |
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Term
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Definition
| Alters the size of a logical block from (usually) 512 bytes to 1,024 bytes. |
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Term
| Constant Linear Velocity (CLV) |
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Definition
| Density of bits per track is uniform. Farther the track from the center, the greater its length, so the more sectors it can hold. |
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Term
| Constant Angular Velocity (CAV) |
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Definition
| Density of bits decreases from inner tracks to outer tracks to keep the data rate constant. |
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Definition
| Storage accessed through local I/O ports. |
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Definition
| Special-purpose storage system that is accessed remotely over a data network. Accessed via remote-procedure-call (RPC) interface such as NFS or CIFS. |
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Definition
| Singular controller card in host; bus architecture supporting a maximum of 16 devices per bus. |
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Term
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Definition
| The storage devices (up to 15) which can be a SCSI disk or also (use of 8 logical units in each SCSI target) used for direct comands to components of a RAID array. |
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Term
| Storage-Area Networks (SANS) |
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Definition
| A private network (using storage protocols rather than networking protocols) connecting serves and storage units. |
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Term
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Definition
| Can address 126 devices (drives and controllers) |
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Term
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Definition
| Latest network-attached storage protocol. Uses IP network protocol to carry the SCSI protocol. |
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Term
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Definition
| Total number of bytes transferred, divided by the total time between the first request for service and the completion of the last transfer. |
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Term
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Definition
| Simplest form of disk scheduling, although not the fastest. |
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Term
| Shortest-Seek-Time-First (SSTF) Scheduling |
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Definition
| Selects the request with the least seek time from the current head position. SSTF chooses the pending request closest to the current head position. |
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Term
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Definition
| Disk arm starts are one end of the disk and moves toward the other end, servicing requests as it reaches each cylinder, until it gets to the other end of the disk. Then movement reversed, and continous scans. |
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Term
| Circular SCAN (C-SCAN) Scheduling |
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Definition
| Once reaching one end of disk, immediately returns to beginning of disk without servicing any requests. |
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Term
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Definition
| In practice, SCAN and C-SCAN go only as far as the final request in each direction before reversing direction immediately, without going all the way to the end of the disk. |
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Term
| Error-Correcting Code (ECC) |
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Definition
| Identifies whether data written may have been corrupted. |
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Term
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Definition
| Recoverable corruption by write detected with ECC. |
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Term
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Definition
| One or more groups of cylinders from a single disk. O.S. treats each partition as if a separate disk. |
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Definition
| Creation of a file system. O.S. stores initial file-system data structures onto the disk. |
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Definition
| Blocks grouped together into larger chunks. Used for effeciency. |
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Term
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Definition
| Stores bootstrap, ROM needs no initialization and is at a fixed rlocation that the processor can start executing when powered up or reset. Cannot be infected by a computer virus since Read Only. |
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Definition
| A disk that has a boot partition. |
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Definition
| The first sector on the hard disk. |
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Term
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Definition
| Win2000 hard-disk partition containing the operating system and device drivers. |
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Term
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Definition
| First sector from the boot partition. |
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Term
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Definition
| Defective very-difficult to fix logical blocks. |
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Term
| Sector Sparing (Forwarding) |
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Definition
| Spare sectors not visable to the operating systems set aside for bad block replacement. |
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Term
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Definition
| Pushes all sectors between spare and defective block up/down so defective sector can be mapped to an empty block. |
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Term
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Definition
| Unrecoverable and results in lost data. Requires manual intervention. |
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Term
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Definition
| Virtual memory uses disk space as an extension of main memory. Significantly decreases system performance. |
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Term
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Definition
| Used to hold swapped pages. |
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Term
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Definition
| An array of integer counters, each corresponding to a page slot in the swap area. |
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Term
| Redundant Arrays of Independent Disks (RAIDS) |
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Definition
| Used for their higher reliability and data-transfer rate. Use of multiple disks in a single array in parallel. A standalone unit with its own controller, cache, and disks. Attached to the host via one or more standard controllers. |
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Term
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Definition
| How long it takes for a single disk to fail. Suppose mean time to failure of a single disk is 100,000 hours. Then mean time to failure of some disk in an array of 100 disks will be 100,000/100 = 1,000 hours or 41.66 days. |
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Term
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Definition
| Solution to the problem of reliability. Storage of extra information that is not normally needed but that can be used in the event of failure of a disk to rebuild the lost information. |
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Term
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Definition
| Duplication of every disk. A logical disk consists of two physical disks, and every write is carried out on both disks. |
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Term
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Definition
| Time it takes (on average) to replace a failed disk and to restore the data on it. If independent, mean time to repair is 10 hours. |
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Term
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Definition
| Failure of one disk is not connected to the failure of another. |
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Term
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Definition
| Time it takes to irrevocably lose data. For a mirrored system: 57,000 years. |
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Term
| Nonvolatile RAM (NVRAM) cache |
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Definition
| Protected from data loss during power failures, so the write can be considered complete at that point, assuming ECC or mirroring is present. |
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Term
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Definition
| Splitting the bits of each byte across multiple disks. |
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Term
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Definition
| Simplest form of data striping. |
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Term
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Definition
| Blocks of a file a striped across multiple disks. |
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Term
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Definition
| Numerous schemes to provide redundancy at lower cost by using disk striping combined with "parity" bits. |
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Term
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Definition
| Automatic duplication of writes between separate sites for redundancy and disaster recovery. Can be synchronous or asynchronous. |
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