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Glossary of IT Infrastructure Library Terms (ITIL®)

Glossary of Terms for the IT Infrastructure Library
Mar 4, 2004

ITSM Watch Staff




data transfer time
The length of time taken for a block or sector of data to be read from or written to an I/O device, such as a disk or tape.


Definitive Software Library (DSL)
The library in which the definitive authorized versions of all software CIs are stored and protected. It is a physical library or storage repository where master copies of software versions are placed. This one logical storage area may, in reality, consist of one or more physical software libraries or filestores. They should be separate from development and test filestore areas. The DSL may also include a physical store to hold master copies of bought-in software, e.g., fireproof safe. Only authorized software should be accepted into the DSL, strictly controlled by Change and Release Management.


The DSL exists not directly because of the needs of the Configuration Management process, but as a common base for the Release Management and Configuration Management processes.


Delta Release
A Delta, or partial, Release is one that includes only those CIs within the Release unit that have actually changed or are new since the last full or Delta Release. For example, if the Release unit is the program, a Delta Release contains only those modules that have changed, or are new, since the last Full Release of the program or the last Delta Release of the modules.


See also "Full Release".


The reliance, either direct or indirect, of one process or activity upon another.


The loss in value of an asset due to its use and/or the passage of time. The annual depreciation charge in accounts represents the amount of capital assets used up in the accounting period. It is charged in the cost accounts to ensure that the cost of capital equipment is reflected in the unit costs of the services provided using the equipment. There are various methods of calculating depreciation for the period, but the Treasury usually recommends the use of current cost asset valuation as the basis for the depreciation charge.


differential charging
Charging business customers different rates for the same work, typically to dampen demand or to generate revenue for spare capacity. This can also be used to encourage off-peak or nighttime running.


direct cost
A cost that is incurred for, and can be traced in full to a product, service, cost center or department. This is an allocated cost. Direct costs are direct materials, direct wages and direct expenses.


See also "indirect cost".


disaster recovery planning
A series of processes that focus only upon the recovery processes, principally in response to physical disasters, that are contained within BCM.


discounted cashflow
An evaluation of the future net cashflows generated by a capital project by discounting them to their present-day value. The two methods most commonly used are:


  • yield method, for which the calculation determines the internal rate of return (IRR) in the form of a percentage
  • net present value (NPV) method, in which the discount rate is chosen and the answer is a sum of money

The offering to business customers of reduced rates for the use of off-peak resources.


See also "surcharging".


disk cache controller
Memory that is used to store blocks of data that have been read from the disk devices connected to them. If a subsequent I/O requires a record that is still resident in the cache memory, it will be picked up from there, thus saving another physical I/O.


Total period that a service or component is not operational, within agreed service times.


duplex (full and half)
Full duplex line/channel allows simultaneous transmission in both directions. Half duplex line/channel is capable of transmitting in both directions, but only in one direction at a time.