X-Modem
: Also known as: Ymodem Y-Modem is an
error-correction protocol used in the transfer of serial data files
between modems. Y-Modem is based on the earlier X-Modem protocol,
but has the additional feature of being able to cope with a batch
transmission mode, in which a number of files can be sent with one
command. For greater efficiency Y-Modem can also handle data with a
variable block size of up to a maximum 1024 bytes (1 kB). During
transmission, the size of text and binary files is included in the
Y-Modem header, so that the exact file length will be retained
after transfer. The error detection method in Y-Modem is cyclic
redundancy check (CRC). A later version of Y-Modem, Y-Modem-G,
transmits data in a continuous stream and does not acknowledge the
blocks successfully received; it is only the blocks with detected
errors that cause a negative acknowledgement (NAK), thus prompting
the resending of data |
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XHTML
: XHTML (a merger of XML and HTML) is an updated
HTML standard introduced to help tidy up all the developments and
additions to original HTML. Over the years, different browsers
added features and offered increased functionality, which all had
their own proprietary manifestation in HTML. This led to a mish
mash of tags and markup that often led to web authors putting in
duplicate attributes and code in order to make sure that a page
looked the same in different browsers browsers. XHTML is a unifying
standard from the W3C that brings the XML benefits of easy
validation and troubleshooting to HTML, which not only helps
developers but also makes the pages easier to read for programs
such as mobile browsers. There are three variations of XHTML, the
most common of which is Transitional. XHTML Transitional is a
stepping stone from the deprecated HTML standardsL, and as such is
fairly permissive, allowing many old and proprietary attributes,
although Transitional stipulates that all tags must have both
opening and a closing markup and be correctly nested. XHTML Strict
is a more rigourous standard that removes all the ’chaff’ gathered
by HTML not ruled out in Transitional, and is what web authors
should strive toward. Finally, XHTML Frameset is similar to XHTML
Transitional, but allows for the use of frames. |
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XML
: extensible markup language |
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