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OC-1 (Optical Carrier Level 1)
OC-1 (Optical Carrier Level 1) is the lowest optical-transmission rate in the SONET standard, 51.48 Mbps.
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Offline viewing
When you make a Web page available offline, you can read its content when your computer is not connected to the
Internet. For example, you can view Web pages on your laptop computer when you don't have a network or Internet
connection. Or you might want to read Web pages at home but do not want to tie up a phone line. You can specify
how much content you want available, such as just a page or a page and all its links, and choose how you want to
update that content on your computer.
If you just want to view a Web page offline, and you don't need to update the content, you can save the page on
your computer. There are several ways you can save the Web page, from just saving the text, to saving all of the
images and text needed to display that page as it appears on the Web.
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OS (Operating System)
Operating System is a software designed to control the hardware of a specific data-processing system in order to
allow users and application programs to employ it easily. Operating System is any hardware / device system which
cannot be operated without a software OS or other controlling system.
Operating System is the most important program that runs on a computer. Every general-purpose computer must have
an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from
the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling
peripheral devices such as disk drives and printers.
For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop,
it makes sure that different programs and users running at the same time do not interfere with each other. The
operating system is also responsible for security, ensuring that unauthorized users do not access the system.
Operating systems can be classified as follows:
Multi-user: Allows two or more users to run programs at the same time. Some operating systems permit hundreds
or even thousands of concurrent users.
Multiprocessing: Supports running a program on more than one CPU.
Multitasking: Allows more than one program to run concurrently.
Multithreading: Allows different parts of a single program to run concurrently.
Real-time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not
real-time.
Operating systems provide a software platform on top of which other programs, called application programs, can
run. The application programs must be written to run on top of a particular operating system. The choice of operating
system, therefore, determines to a great extent the applications that can be run. For PCs, the most popular operating
systems are DOS, OS/2, and Windows, but others are available, such as Linux.
Users normally interact with the operating system through a set of commands. For example, the DOS operating system
contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The
commands are accepted and executed by a part of the operating system called the command processor or command line
interpreter. Graphical user interfaces allow to enter commands by pointing and clicking at objects that appear
on the screen.
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OSI (Open Systems Interconnection)
OSI (Open Systems Interconnection) reference model has been defined by the International Standards Organization
(ISO). This is a seven layer architecture.
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7 - Application Layer
Consists of application programs that use the network.
6 - Presentation Layer
Standardizes data presentation to the applications that use the network.
5 - Session Layer
Manages sessions between applications.
4 - Transport Layer
Provides end-to-end error detection and correction.
3 - Network Layer
Manages connections across the network for the Upper Layers.
2 - Data Link Layer
Provides reliable data delivery across the physical link.
1 - Physical Layer
Defines the physical characteristics of the network media. |
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