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Basic Computer Skills
Notes length, languages, media descriptors, colors, character encodings, dates and times, and so on.
All of these data types are specializations of character data.
13.6.2 Document Type Declaration
HTML documents are required to start with a Document Type Declaration (informally, a “doctype”).
In browsers, the doctype helps to define the rendering mode—particularly whether to use quirks
mode.
The original purpose of the doctype was to enable parsing and validation of HTML documents
by SGML tools based on the Document Type Definition (DTD). The DTD to which the
DOCTYPE refers contains a machine-readable grammar specifying the permitted and
prohibited content for a document conforming to such a DTD. Browsers, on the other hand,
do not implement HTML as an application of SGML and by consequence do not read the
DTD. HTML5 does not define a DTD, because of the technology’s inherent limitations, so in
HTML5 the doctype declaration, <!doctype html>, does not refer to a DTD.
An example of an HTML 4 doctype is
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.01//EN” “http://www.w3.org/TR/
html4/strict.dtd”>
This declaration references the DTD for the ‘strict’ version of HTML 4.01. SGML-based
validators read the DTD in order to properly parse the document and to perform
validation. In modern browsers, a valid doctype activates standards mode as opposed to
quirks mode.
Web pages are written in HTML (hypertext markup language) and are
translated by your Web browser. Web pages can either be static or dynamic.
Static pages show the same content each time they are viewed. Dynamic
pages have content that can change each time.
13.7 Internet Service Provider (ISP)
An Internet service provider (ISP) is a company that provides access to the Internet, hosts
data, or does both. Access ISPs connect customers to the Internet using copper, wireless or
fiber connections. Hosting ISPs lease server space for smaller businesses and host other
people servers (colocation). Transit ISPs provide large tubes for connecting hosting.
13.7.1 Access ISPs
ISPs employ a range of technologies to enable consumers to connect to their network.
For users and small businesses, the most popular options include dial-up, DSL (typically
Asymmetric Digital Subscriber Line, ADSL), broadband wireless, cable modem, fiber to the
premises (FTTH), and Integrated Services Digital Network (ISDN) (typically basic rate
interface). For customers with more demanding requirements, such as medium-to-large
businesses, or other ISPs, DSL (often SHDSL or ADSL), Ethernet, Metro Ethernet, Gigabit
Ethernet, Frame Relay, ISDN (BRI or PRI), ATM, satellite Internet access and synchronous
optical networking (SONET) are more likely to be used.
Internet connectivity options from end-user to Tier 3/2 ISP’s
Typical home user connection
Broadband wireless access
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