Extron Electronics MS9500 HD FrEND Plus - Manual (Page 105)

MS950GL HD FrEND Plus Glossary
Pan and Scan The technique used to crop a widescreen picture to conventional 4:3 television
ratio, while panning the original image to follow the on-screen action
PID: Program ID. An MPEG transport stream can contain multiple elementary
streams of media, such as audio and video. Each of these streams are uniquely
identified by a 16 bit number called the PID number.
Progressive Short for progressive scanning. A system of video scanning whereby lines of a
picture are transmitted consecutively, such as in the computer world
Protocol Set of syntax rules defining exchange of data including items such as timing,
format, sequencing, error checking, etc.
PSIP Program and system information protocol. A part of the ATSC digital television
specification that enables a DTV receiver to identify program information from
the station and use it to create easy-to-recognize electronic program guides for
the viewer at home. The PSIP generator inserts data related to channel selection
and electronic program guides into the ATSC MPEG transport stream.
RAID Redundant array of independent disks. A grouping of standard disk drives
together with a RAID controller to create storage that acts as one disk to provide
performance beyond that available from individual drives. Primarily designed
for operation with computers RAIDs can offer very high capacities, fast data
transfer rates and much-increased security of data. The latter is achieved through
disk redundancy so that disk errors or failures can be detected and corrected.
A series of RAID configurations is defined by levels and, being designed by
computer engineers, they start counting from zero. Different levels are suited to
different applications.
Level 0: No redundancy-benefits only of speed and capacity-generated by
combining a number of disks. Also known as "striping."
Level 1: Complete mirror system-two sets of disks both reading and writing the
same data. This has the benefits of level 0 plus the security of full redundancy-
but at twice the cost. Some performance advantage can be gained in read
because only one copy need be read, so two reads can occur simultaneously.
Level 2: An array of nine disks. Each byte is recorded with one bit on each of
eight disks and a parity bit recorded to the ninth. This level is rarely, if ever,
used.
Level 3: An array of n+1 disks recording 512 byte sectors on each of the n disks
to create n x 512 "super sectors" + 1 x 512 parity sector on the additional disk
which is used to check the data.
The minimum unit of transfer is a whole superblock. This is most suitable for
systems in which large amounts of sequential data are transferred, such as for
audio and video. For these it is the most efficient RAID level since it is never
necessary to read/modify/write the parity block. It is less suitable for database
types of access in which small amounts of data need to be transferred at random.
Level 4: The same as Level 3 but individual blocks can be transferred. When
data is written it is necessary to read the old data and parity blocks before
writing the new data as well as the updated parity block, which reduces
performance.
Level 5: The same as Level 4, but the role of parity the disk is rotated for each
block. In level 4 the parity disk receives excessive load for writes and no load for
reads. In Level 5 the load is balanced across the disks.
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