| slovo | definícia |
fdd
(foldoc) | disk drive
FDD
floppy disk drive
floppy drive
(Or "hard disk drive", "hard drive",
"floppy disk drive", "floppy drive") A peripheral device
that reads and writes hard disks or floppy disks. The
drive contains a motor to rotate the disk at a constant rate
and one or more read/write heads which are positioned over the
desired track by a servo mechanism. It also contains the
electronics to amplify the signals from the heads to normal
digital logic levels and vice versa.
In order for a disk drive to start to read or write a given
location a read/write head must be positioned radially over
the right track and rotationally over the start of the right
sector.
Radial motion is known as "seeking" and it is this which
causes most of the intermittent noise heard during disk
activity. There is usually one head for each disk surface and
all heads move together. The set of locations which are
accessible with the heads in a given radial position are known
as a "cylinder". The "seek time" is the time taken to
seek to a different cylinder.
The disk is constantly rotating (except for some floppy disk
drives where the motor is switched off between accesses to
reduce wear and power consumption) so positioning the heads
over the right sector is simply a matter of waiting until it
arrives under the head. With a single set of heads this
"rotational latency" will be on average half a revolution
but some big drives have multiple sets of heads spaced at
equal angles around the disk.
If seeking and rotation are independent, access time is seek
time + rotational latency. When accessing multiple tracks
sequentially, data is sometimes arranged so that by the time
the seek from one track to the next has finished, the disk has
rotated just enough to begin accessing the next track.
See also sector interleave.
Early disk drives had a capacity of a few megabytes and were
housed inside a separate cabinet the size of a washing
machine. Over a few decades they shrunk to fit a terabyte
or more in a box the size of a paperback book.
The disks may be removable disks; floppy disks always are,
removable hard disks were common on mainframes and
minicomputers but less so on microcomputers until the mid
1990s(?) with products like the Zip Drive.
A CD-ROM drive is not usually referred to as a disk drive.
Two common interfaces for disk drives (and other devices) are
SCSI and IDE. ST-506 used to be common in
microcomputers (in the 1980s?).
(1997-04-15)
|
fdd
(vera) | FDD
Floppy Disk Drive
|
fdd
(vera) | FDD
Frequency Division Duplex (mobile-systems)
|
| | podobné slovo | definícia |
fddi
(encz) | FDDI,Fiber Distributed Data Interface [zkr.] [voj.] Zdeněk Brož a
automatický překlad |
fdd
(foldoc) | disk drive
FDD
floppy disk drive
floppy drive
(Or "hard disk drive", "hard drive",
"floppy disk drive", "floppy drive") A peripheral device
that reads and writes hard disks or floppy disks. The
drive contains a motor to rotate the disk at a constant rate
and one or more read/write heads which are positioned over the
desired track by a servo mechanism. It also contains the
electronics to amplify the signals from the heads to normal
digital logic levels and vice versa.
In order for a disk drive to start to read or write a given
location a read/write head must be positioned radially over
the right track and rotationally over the start of the right
sector.
Radial motion is known as "seeking" and it is this which
causes most of the intermittent noise heard during disk
activity. There is usually one head for each disk surface and
all heads move together. The set of locations which are
accessible with the heads in a given radial position are known
as a "cylinder". The "seek time" is the time taken to
seek to a different cylinder.
The disk is constantly rotating (except for some floppy disk
drives where the motor is switched off between accesses to
reduce wear and power consumption) so positioning the heads
over the right sector is simply a matter of waiting until it
arrives under the head. With a single set of heads this
"rotational latency" will be on average half a revolution
but some big drives have multiple sets of heads spaced at
equal angles around the disk.
If seeking and rotation are independent, access time is seek
time + rotational latency. When accessing multiple tracks
sequentially, data is sometimes arranged so that by the time
the seek from one track to the next has finished, the disk has
rotated just enough to begin accessing the next track.
See also sector interleave.
Early disk drives had a capacity of a few megabytes and were
housed inside a separate cabinet the size of a washing
machine. Over a few decades they shrunk to fit a terabyte
or more in a box the size of a paperback book.
The disks may be removable disks; floppy disks always are,
removable hard disks were common on mainframes and
minicomputers but less so on microcomputers until the mid
1990s(?) with products like the Zip Drive.
A CD-ROM drive is not usually referred to as a disk drive.
Two common interfaces for disk drives (and other devices) are
SCSI and IDE. ST-506 used to be common in
microcomputers (in the 1980s?).
(1997-04-15)
|
fddi
(foldoc) | Fiber Distributed Data Interface
FDDI
(FDDI) A 100 Mbit/s ANSI standard local area network
architecture, defined in X3T9.5. The underlying medium is
optical fibre (though it can be copper cable, in which case
it may be called CDDI) and the topology is a
dual-attached, counter-rotating token ring.
FDDI rings are normally constructed in the form of a "dual
ring of trees". A small number of devices, typically
infrastructure devices such as routers and concentrators
rather than host computers, are connected to both rings -
these are referred to as "dual-attached". Host computers
are then connected as single-attached devices to the
routers or concentrators. The dual ring in its most
degenerate form is simply collapsed into a single device. In
any case, the whole dual ring is typically contained within a
computer room.
This network topology is required because the dual ring
actually passes through each connected device and requires
each such device to remain continuously operational (the
standard actually allows for optical bypasses but these are
considered to be unreliable and error-prone). Devices such as
workstations and minicomputers that may not be under the
control of the network managers are not suitable for
connection to the dual ring.
As an alternative to a dual-attached connection, the same
degree of resilience is available to a workstation through a
dual-homed connection which is made simultaneously to two
separate devices in the same FDDI ring. One of the
connections becomes active while the other one is
automatically blocked. If the first connection fails, the
backup link takes over with no perceptible delay.
Usenet newsgroup: news:comp.dcom.lans.fddi.
(1994-12-13)
|
fdd
(vera) | FDD
Floppy Disk Drive
FDD
Frequency Division Duplex (mobile-systems)
|
fddi
(vera) | FDDI
Fiber Distributed Data Interface (ANSI, ISO 8314)
|
fdditppmd
(vera) | FDDITPPMD
FDDI Twisted Pair-Physical layer, Medium Dependent, "FDDI TP-PMD"
|
wcdmafdd
(vera) | WCDMAFDD
Wide-band Code Division Multiple Access - Frequency Division
Duplex (UMTS, mobile-systems), "WCDMA-FDD"
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