| Data
Transfer Time |
Data
transfer time is 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 disc or tape. |
|
|
| Database
Management System |
A
management system associated
with a structured set of data
that allows the data to be
accessed in a variety of
ways. In a Relational
DBMS, the relationships between
the data elements form keys to
reduce the amount of data
needing to be held and to
improve navigation and access
speeds. |
|
|
| Definitive
Hardware Store |
A
location, or a number of
locations, set aside for the
secure storage of definitive
hardware spares maintained at
the same level as the equivalent
hardware CIs
in the live environment.
Only authorised hardware should
be accepted into the DHS,
strictly controlled by Change
and Release Management. |
|
|
| Definitive
Software Library |
A
physical library where all
quality-controlled versions of
all software CIs are held in
their definitive form, together
with any associated CIs such as
licence and other
documentation. 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. Only
authorised software should be
accepted into the DSL, strictly
controlled by Change and Release
Management. |
|
|
| Deliverable |
An
item which must be created as
part of a stated
requirement. It may be a
final product or one on which
one or more subsequent
deliverables are dependant. |
|
|
| Delivering
Information Systems to Customers |
DISC
is the organisation within the
BSI that helps enterprises
improve their operational
effectiveness by accelerating
standardisation of information
systems by promoting standards
and making them easier to
exploit. |
|
|
| Delta
Release |
A
release that does not replace
all component CIs
within a release unit, but
rather includes only those CIs
that have changed since the last
release of the software.
Sometimes referred to as a
'partial' release. |
|
|
| Demand
Management |
Influencing
the use of IT capacity, perhaps
by incentive or penalty, in
circumstances where unmanaged
demand is likely to exceed the
ability to deliver. Demand
Management is achieved by
assigining resources according
to priorities. |
|
|
| Deming |
In
his book 'Out of the Crisis', W.
Edwards Deming described 14
points that lie at the heart of
quality improvement. Since
the ITSM
philosophy is essentially one of
continuous
improvement, those 14 points
apply, and any ITSM initiative
that ignores them does so at its
peril. They include:
 | Constancy
of purpose toward
improvement of product and
service |
| Cease
dependence on inspection to
achieve quality by building
quality into the service. |
| Award
business on the basis of
total cost rather than the
'price tag'. |
| Improve
constantly and forever the
system of production and
service, to improve quality
and productivity, and thus
constantly decrease costs. |
| Institute
training on the job. |
| Institute
leadership. The aim of
supervision is to help
people and machines do a
better job. |
| Break down
barriers between
departments. Everyone
must work as a team to foresee
problems of production and
in use that may be
encountered with the product
or service. |
| Institute a
vigorous programme of education
and self-improvement. |
| Put
everybody in the
organisation to work to
accomplish the
transformation. The
transformation is
everybody's job. |
|
|
|
| Dependency |
The
direct or indirect reliance of
one process or activity upon
another. |
|
|
| Depreciation |
Depreciation
is the measure of the reduction
in the useful economic life of a
capital item. It will take
into account the current value
of the asset, the expected
remaining length of life and any
residual value of the asset at
the end of its useful
life. Finance departments
will give guidance on the method
of depreciation to be employed. |
|
|
| Detection |
The
second stage, after Occurrence,
in an Incident life-cycle when
the service failure becomes known
to the IT service organisation. |
|
|
| Diagnosis |
The
third stage, after Detection,
in an Incident life-cycle during
which the service provider seeks
to understand the root cause of
the failure. |
|
|
| Diagnostic
Script |
A
structured set of questions used
by the Service Desk staff to
enable faster resolution and/or
more accurate assignment of
Incidents. Diagnostic
scripts will often be provided
and maintained by technical
staff as one of their Incident
Management process
responsibilities. |
|
|
| Disaster
Recovery |
See
IT Service Continuity Management. |
|
|
| Differential
Charging |
A
charging policy aimed either at
dampening the demand for a
scarce or expensive resource or
encouraging the use of spare
capacity. |
|
|
| Direct
Cost |
A
cost which can be allocated in
full to a product, service,
customer, cost centre or
business activity. A group
of staff dedicated to developing
a Customer application is an
example. |
|
|
| Disaster
Recovery Planning |
The
processes within Business
Continuity Management that
focus upon recovery from,
principally, physical
disasters. |
|
|
| Discounted
Cash Flow |
A
means of evaluating the future
net cash flows generated by a
capital project by discounting
them to their present-day
value. Two methods
commonly employed are the 'yield
method', where the calculation
determines a percentage IRR
and the 'NPV
method', where a given discount
rate will generate sums of money
for comparison. |
|
|
| Disk
Cache Controller |
Disk
cache controllers have memory
which is used to store blocks of
data which 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. |
|
|
| Do
Nothing |
An
IT Service Continuity Planning
option that, positively, decides
to take no additional technical
or managerial action to reduce
the impact of a disastrous loss
of service, other, perhaps, than
to take out an insurance
policy. Because of the
importance of most IT service
this is rarely an option
exercised (except by default!). |
|
|
| Document |
Information
in readable form, including
computer data, which is created
or received and maintained as
evidence of the service
provider's intentions.
Records are distinguished from
documents by the fact that they
function as evidence of
activities, rather than evidence
of intentions. Examples
include policy statements,
plans, procedures, Service Level
Agreements and contracts. |
|
|
| Domain |
See
IT Infrastructure Domain. |
|
|
| Dormant
Contract |
A
contract in which a supplier
agrees, perhaps for a premium,
to supply a product or service
on demand, usually in response
to an unplanned event. |
|
|
| Downtime |
The
total period that a service or
component is not operational
within an agreed service
time. Measured from when a
service or component fails to
when normal operations
recommence. |
|
|
| Duplex
(Full and Half) |
Duplex
equipment provides two, usually
identical, IT components each of
which is capable of performing
the full task if the other
fails. Full
duplex line/ channel allows
simultaneous transmission in
both directions. Half duplex/
channel is capable of
transmitting in both directions,
but only one direction at a
time. |
