M

MAPI : Messaging Applications Programming Interface. Programming Interface specification that enables an application to send and receive mail over a Microsoft Mail messaging system.

Main frame : A computer primarily used by Global 2000 corporations for large-scale commercial applications. A mainframe is capable of supporting many users from many terminals.

MB : See megabyte.

Media : The material or device used to store information in a storage subsystem, such as a tape or disk drive. DLTtape media is a high-grade metal particle (MP) formulation that takes advantage of the latest advances in binder chemistry. By combining both solid and liquid lubricants in the tape binder system, tape and head wear are reduced while repelling airborne particles that could affect read/write head performance. In addition, by using a uniform particle shape, a dense binding system, a smooth coating surface, and a specially selected base film, Quantum DLTtape half-inch cartridge tapes take advantage of shorter wavelength recording schemes to ensure read compatibility with future generations of DLT drives.

Megabyte (MB) : A unit of measurement equal to 1 million bytes.

Megahertz (MHz) : A measurement of frequency in millions of cycles per second.

Metal Particle (MP) tape : A magnetic recording media in which a flexible base is coated with a mixture of magnetic particles and a bonding agent. See also Media.

Metadata : The information that is associated with a file but separate from data in the file; required to identify data in the file and its physical location on a disk.

MHz : See megahertz.

Microprocessor : The integrated circuit chip that performs the bulk of data processing and controls the operation of all of the parts of the system.

Microsecond (µs) : One millionth of a second (.000001 sec.).

Millisecond (ms) : One thousandth of a second (.001 sec.).

Minicomputer : A somewhat out-of-date term used to describe a class of multi-user computer that was one notch below a mainframe system. Minicomputer popularity fell with the rise in popularity of the networked PC. Today's server systems perform many of the functions that were once the domain of minicomputers.

Mirroring : A data redundancy technique in which data is recorded identically and simultaneously on multiple separate disks. When the primary disk is off-line the alternate takes over, providing continuous access to data. Defined as RAID 1 configuration.

Mission Critical : Applications that are vital to a company or organization's well-being.

Modularity : An approach to developing hardware or software that breaks projects into smaller units (or modules) that are deliberately designed as standalone units that can work with other sections of the program. The same module can perform the same task in another or several other programs or components. Modifying the way that module works will have no adverse affects on the other components of a program.

MTBF : Acronym for mean time between failure. Reliability rating indicating the expected failure rate of a product in power on hours (POH). Since manufacturers differ in the ways they determine the MTBF, comparisons of products should always take into account the MTBF calculation method.

MTTR : Acronym for mean time to repair. The average time it takes to repair a drive that has failed for some reason. This only takes into consideration the changing of the major subassemblies such as the circuit board or sealed housing. Component-level repair is not included in this number as this type of repair cannot be performed in the field.

Multipathing : Multipathing allows for two or more data paths to be simultaneously used for read/write operations, enhancing performance by automatically and equally dispersing data access across all the available paths.

N

Name Services Login : Worldwide-exclusive names that allow a device to log into the switch.

NAS : Network-Attached Storage. Storage connected directly to the network, through a processor and its own operating system. Lacks the processor to run centralized share applications.

Native Mode : Refers to the uncompressed storage capacity of a tape or disk subsystem. For instance, a DLT 7000 tape drive can store 35 GB in native mode and 70 GB with 2:1 compression.

Near-On-Line Storage : An application that uses a tape drive or tape automation system in much the same way as a hard disk drive. Provides easy access to large amounts of critical information.

NFR : Near Field Recording. A recording technology developed by TeraStor combining optical and current HDD recording technology. It promises recording densities up to 10 times that currently available.

Nonvolatile : Data in memory, cache and other electronic repositories are protected by a battery backup system to prevent their loss in the event of a power failure.

NUMA : Nonuniform Memory Access. A form of SMPP, also known as shared memory cluster (SMC). A hybrid between symmetrical multiprocessing and clustering. Arranges multiple processors into small groups of processors, all of which communicate with each other. Designed to extend scalability beyond the SMP system bottlenecks. Memory is logically shared.

O

OEM : Acronym for Original Equipment Manufacturer.

Overhead : Command overhead refers to the processing time required by the controller, host adapter, or drive prior to the execution of a command. Lower command overhead yields higher drive performance.

Overwrite : To write data on top of existing data thus erasing the original data.

OLTP : Online Transaction Processing is a system that processes transactions the instant the computer receives them and updates master files immediately. OLTP is essential for good financial record keeping and inventory tracking.

P

Parallel Channel Architecture : Allows DLT tape drives to read/write multiple channels simultaneously providing an fast data transfer rate (e.g. in the DLT 7000 tape drive). With this architecture, data blocks are not required to be located on any particular track or in consecutive order. This channel-independent block structure provides a powerful write-error handling system that allows bad blocks to be rewritten on the next available channel.

Partial Response, Maximum Likelihood (PRML) : A technology that allows a disk or tape drive's read channel to pack more data in the same amount of space on magnetic media.

Parity : A data-error-checking procedure where the number of 1s must always be the same—either even or odd— for each group of bits submitted without error. Parity information is saved and compared with each subsequent calculations of whether the number is odd or even.

Parity Bit : An extra bit used in checking for errors in transferred groups of data bits. In modem communications, it is used to check the accuracy of each transmitted character. In RAM, a parity bit is used to check the accuracy with which each byte is stored.

Peak Transfer Rate : The maximum speed with which information moves inside a tape drive or between drive and host. Usually measured in megabytes per second.

Peripheral : A device added to a system as a complement to the basic CPU, such as a disk drive, tape drive, or printer.

PB (PetaByte) : One quadrillion bytes or one thousand terabytes.

POH : Acronym for Power-on Hours. The unit of measurement for mean time between failure (MTBF), expressed as the number of hours that the system or drive is powered on. See MTBF.

Port : On a computer, it is a physical connecting point to which a device is attached.

PRML : See partial response, maximum likelihood.

Protocol : A set of rules or standards intended to enable computers to communicate.