| ADSM
| 'ADSTAR Distributed Storage Manager'
| An IBM product used to manage backup and recovery of data from a variety of non-mainframe servers. Recently renamed to Tivoli Storage Manager
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| API
| 'Application Programming Interface'
| An interface which can be used to communicate with another vendors product to provide add-on functionality.
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| Cluster
| 'A Lotus Notes Term'
| A cluster consists of between 2 and 6 Domino servers, and is managed by the Cluster Manager.
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| Domain
| 'A Lotus Notes Term'
| A Domain is all servers which share a common, public NAMES.NSF Address book.
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| FC-AL
| 'Fibre Channel Arbitrated Loop'
| FC-AL is an network which daisy chains all the attached storage devices onto a fibre channel.
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| HSM
| 'Heirarchical Storage Manager'
| More Properly, DFSMSHSM, an IBM product which is used to migrate data off disk onto tape, if it has not been referenced for a set number of days
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| JBOD
| 'JUST A BUNCH OF DISKS'
| A strange acronyn that is pretty meaningless out of context. What it means is that the disk group is not RAID, that is there is no failover redundancy.
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| JCL
| 'JOB CONTROL LANGUAGE'
| The Language used by IBM to define batch processing work. It basically identifies a set of programs, and what their input and output data sources will be.
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| KSDS
| 'Key Sequence DataSet'
| A type of VSAM dataset allocated under IBM Mainframe operating systems. A KSDS has at least three components, data, an index which allows direct access to the data, and a cluster which holds it all together. A KSDS can also have a number of alternate indices.
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| LRU
| 'LEAST RECENTLY USED'
| An algorithm used to determine how space is reclaimed in temporary memory, when it starts to fill up. an LRU algorithm swaps out data which has not been accessed for some time. Contrast with LIFO (Last in First out)
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| LCD
| 'Liquid Crystal Display'
| A crystalline structure with optical properties which can be changed by the application of an electric field. The polarisation of the Molecules within the LCD affects the way the light is transmitted. Applications vary between a simple digital readout, where the polarisation generates a dark line, or nothing, to a complex coloured display for a portable PC.
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| LSR
| 'Local Shared Resource'
| An OS/390 method of keeping data in memory, to prevent applications going out to disk.
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| Management Class
| 'Management Class'
| A DFSMS construct for managing mainframe data. Each management class contains parameters which determine how long a dataset spends at each stage of the storage heirarchy, and how often it gets backed up
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| MVS
| 'Multiple Virtual Storage'
| an older name for IBM's OS/390 operating system
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| OS/390
| 'Operating System 390'
| IBM's flagship mainframe operating system, formerly called MVS
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| pixel
| 'picture element'
| a single square in an image
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| RAID5
| 'Redundant array of independent disks - level 5'
| A method of protecting data from failure of a single disk. The data is written in blocks, spread over a group of disks. One of the disks in the group contains parity data from which the data can be reconstructed, if a disk fails. The parity is not held on a dedicated disk, but is spread over the whole group.
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| Seek Time
| The time taken to locate a track or cylinder on a disk
| Data on a physical hard drive is read by moving a magnetic head over the surface, until the required track is below the head. 'Seek time' is the average time it takes to position the head over the data. Seek time is almost eliminated in disk devices with large solid state caches, as the data is prestaged in the cache, before it is needed.
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| SRDF
| 'Symmetrix Remote Data Facility'
| EMCs product which permits disk storage mirroring between two remote sites
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| SMS
| IBM 'Storage Management Subsystem'
| A set of utilities used to allocate, expire, backup and archive data on an OS/390 mainframe. PC term is DFSMS
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| SMS
| Microsoft 'System Management Software'
| A suite of programes used by Microsoft to manage NT servers
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| TDMF
| 'Transparent Data Migration Facility'
| A software product which allows seamless movement of open files
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| TSO
| 'Time Sharing Option'
| An interactive function of MVS, which lets a user work in the foreground to edit files, etc.
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| UCB
| 'UNIT CONTROL BLOCK'
| An OS/390 term. It is a hexadecimal number which is used to identify ant hardware item to the operating system
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| VSAM
| 'Virtual Storage Access Method'
| An OS/390 based data type, with various flavours for sequential, indexed or unstructured files
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