Internet Phone (Soft Phone)
A popular VoIP application. There are actually
two different products called Internet Phone, one
produced by Intel and the other developed by
Short for Voice over Internet Protocol, a category
of hardware (mic & speaker) and software (e.g.
CoolTalk, NetMeeting + msn messenger, Skype,
NetTalk, ICQ phone, Yahoo messenger voice
chat, QQ) that enables people to use the Internet
as the transmission medium for telephone calls
by sending voice data in packets using IP rather
than by traditional circuit transmissions of the
PSTN (Public Switched Telephone Network).
Advantage: no surcharge (except for Internet
access) like sending e-mails over the Internet,
data compression, higher bandwidth
VoIP also is referred to as Internet telephony, IP
telephony, or Voice over the Internet (VOI)
DNS (Domain Name System) http://en.wikipedia.org/wiki/Category:Domain_Name_System
The Domain Name System is a distributed database. This allows local control of the
segments of the overall database, yet data in each segment are available across the entire
network through a client-server scheme. Robustness and adequate performance are
achieved through replication and caching.
Programs called Name Server comprise the server half of DNS's client server mechanism.
Name servers contain information about some segment of the database and make it
available to clients, called Resolvers. Resolvers are often just library routines that create
queries and send them across a network to a name server.
The whole database is like an inverted tree, with the root at the top. The first row of the
name is the last part (TLD) of the domain name, which is either "com", "net", "edu", "gov",
"mil", ... Or a two letter country code, like "tw" for Taiwan, "uk" for United Kingdom, "th" for
Thailand, ... followed by the next row with, "com", "net", "edu", "gov", "mil", ... In the next
row we find the name of the domain, and in below rows we find the sub domains and
The name of the domain is like the name of a person, and the IP address is like his phone
number. We call a person with the phone by dialing the phone number. On the Internet we
have IP numbers for each host (computer, server, router, ...), and we give these IP
numbers an easy to remember name, which are organized into the domain name. If you
are connected to the Internet, DNS is therefore a must.
Top Level Domain (TLD)
TLD identifies the most general part of the domain name in an Internet address.
A TLD is either a generic top-level domain (gTLD), such as "com" for "commercial," "edu"
for "educational," and so forth, or a country code top-level domain (ccTLD), such as "fr" for
France, "cn" for China, "hk" for Hong Kong or "is" for Iceland.
If the host is permanent connected to the Internet, than the computer will have got a
permanent IP address, which is under IPv4 something like 126.96.36.199, a group of 4
numbers which can have the values up to 255 each. A static IP address will be provided to
the computer from the ISP where the computer is connected. The ISP has got a range of
IP addresses, which it distributes to their customers. All hosts are in a (static) database of
a DNS. All names are resolved to their IP address.
If the host is not permanent connected to the Internet, than the computer will get a
temporary IP address assigned from the ISP. These dynamic IP addresses are random
assigned out of a pool of the ISP. Usually all dialup accounts will get a dynamic IP address.
That means, as soon the user does not need to be connected to the Internet anymore, this
IP address falls back into the pool for re-use by another dialup user. Usually a dialup user
do not run a server, therefore he does not need static IP address.
Dynamic DNS (Domain Name System)
a method of keeping a domain name linked to a changing IP address as not all computers
use static IP addresses. Typically, when a user connects to the Internet, the user's ISP
assigns an unused IP address from a pool of IP addresses, and this address is used only
for the duration of that specific connection. This method of dynamically assigning
addresses extends the usable pool of available IP addresses. A dynamic DNS service
provider uses a special program that runs on the user's computer, contacting the DNS
service each time the IP address provided by the ISP changes and subsequently updating
the DNS database to reflect the change in IP address. In this way, even though a domain
name's IP address will change often, other users do not have to know the changed IP
address in order to connect with the other computer
http://www.technopagan.org/dynamic/ (Dynamic DNS Providers List)
Every time your computer (as a server, with domain name abc.com) is new connected to
the Internet, it first checks its own (new) IP address and requests an update of the
dynamic DNS automatically. The update is done within a second. Users who are accessing
your server will be guided to the new IP address automatically.
UPS (uninterruptible power supply)
a power supply that includes a battery to maintain power in the event of a power outage.
Typically, a UPS keeps a computer running for several minutes after a power outage,
enabling you to save data that is in RAM and shut down the computer gracefully. Many
UPSs now offer a software component that enables you to automate backup and shut
down procedures in case there's a power failure while you're away from the computer.
a protection scheme based on ASA (ASA tracks the source and destination address, TCP
sequence numbers, port numbers, and additional TCP flags of each packet), which offers
stateful connection-oriented security. This information is stored in a table, and all inbound
and outbound packets are compared against entries in the table
Adaptive Security Algorithm
The ASA (Adaptive Security Algorithm) is the heart of the PIX Firewall
ASA is stateful and connection oriented
The ASA design creates session flows based on:
Source and destination addresses
TCP sequence numbers
By applying the security policy to the connection table entries, inbound and outbound
traffic can be controlled
Refers to objects that you can actually touch, like disks, disk drives, display screens,
keyboards, printers, boards, and chips. In contrast, software is untouchable. Software
exists as ideas, concepts, and symbols, but it has no substance.
Books provide a useful analogy. The pages and the ink are the hardware, while the
words, sentences, paragraphs, and the overall meaning are the software. A computer
without software is like a book full of blank pages -- you need software to make the
computer useful just as you need words to make a book meaningful.
Computer instructions or data. Anything that can be stored electronically is software.
The storage devices and display devices are hardware.
Software is often divided into two categories:
systems software : Includes the operating system and all the utilities that
enable the computer to function.
applications software : Includes programs that do real work for users. For
example, word processors, spreadsheets, and database management systems
fall under the category of applications software.
Firmware is programming that is inserted into programmable read-only memory
(programmable ROM), thus becoming a permanent part of a computing device.
Firmware is created and tested like software (using microcode simulation). When ready,
it can be distributed like other software and, using a special user interface, installed in
the programmable read-only memory by the user. Firmware is sometimes distributed for
printers, modems, and other computer devices.
Software (programs or data) that has been written onto read-only memory (ROM).
Firmware is a combination of software and hardware. ROMs, PROMs and EPROMs that
have data or programs recorded on them are firmware.
Refers to the operating system and all utility programs that manage computer resources
at a low level. Software is generally divided into systems software and applications
software. Applications software comprises programs designed for an end user, such as
word processors, database systems, and spreadsheet programs. Systems software
includes compilers, loaders, linkers, and debuggers.
Word Processing Graphics Spreadsheets
Communications Database Games
Assembler Debugger Compilers
File Management Tools Operating System Utilities
Comparison between LCD monitors and CRT monitors
PC monitors are not all the same any more. There are two types of monitors that are
being widely used. CRT (Cathode Ray Tube) monitors are the traditional monitors that
we have been using for years. LCD (Liquid Crystal Display) monitors are now becoming
popular, because of their great space saving advantage. Now, let's take a look at some
of the differences between the LCD monitors and CRT monitors.
One of the greatest advantages of LCD monitors is that they are more compact and
lightweight compared with CRT monitors. LCD monitors take up less room, so they can
be used in many places where a larger CRT monitor cannot fit.
Side view of an LCD monitor & CRT monitor
Brightness and Colours
LCD screens are generally not as bright as CRT screens. Many LCD monitors are
only capable of displaying thousands of colours, while CRT monitors are capable of
displaying unlimited colours.
Most LCD monitors (15”) available on the market have maximum resolutions of 1024
5 768. A 15” CRT monitor, although has a slightly smaller viewing area than a typical
15” LCD monitor, is capable of displaying a maximum resolution of 1280 5 1024.
LCD monitors have a much smaller viewing angle than that of CRT monitors. A CRT
screen can be viewed from its side, whereas an LCD screen can only be viewed
directly from its front. If a person looks at an LCD screen from the side, the image on
the screen may seem to disappear or the colour of the image may not be so clear.
Viewing angle of an LCD monitor and a CRT monitor
Power Consumption and Radiation Emission
LCD monitors are generally more environmental friendly than CRT monitors. LCD
monitors produce less heat. They consume less energy than CRT monitors. Besides,
LCD monitors do not emit harmful radiation as CRT monitors do.
By better technology and higher volume of production, LCD monitors not only
become less and less expensive, but also provide better quality in display
characteristics (brightness, clearness and sharpness). It is believed that more
consumers will switch from the conventional CRT monitors to LCD monitors in the
PDA stands for Personal Digital Assistant, which is a hand-held computer that allows
users to store, access, and organize information. A variety of PDAs such as Pocket PC,
Handheld Organizer, or Palms are available on markets. The prices of most PDAs range
from $100 to $600.
PDAs have built-in memory range from 2MB to 64 MB.
Memory of some PDAs can be expanded by inserting small
storage cards. PDAs range from the size and thickness of 10
business cards, weighing 40 grams, to the size of a pocket-
sized book weighing significantly more.
Users have to use a pen-like stylus to input data into most of
the PDAs. Users can either enter data by tapping on an on-
screen keyboard or enter data by writing on the screen.
PDAs are equipped with almost everything one might need
from a computer when on the move. Basic PDAs allows
users to store and retrieve addresses, phone numbers, maintain a calendar, and
creating to-do lists and notes. More sophisticated PDAs can run word processing,
spreadsheet, money manager, games and electronic book reading programs, they
contain fax functionality and also provide wireless access to e-mail and the Internet.
Moreover, PDA can also easily share information with Windows-based or Macintosh
computers easily, that allow users to transfer files and synchronize the data on both the
PDA and the laptop computer. PDA can transfer the information to other PDAs with
infrared technology. In fact, there are thousands of programs that can increase the
efficiency and power of the PDAs. The users can simply upgrade the programs by
downloading the software from the Internet.
What is Bluetooth?
Bluetooth is the name of a new technology standard for a small, cheap radio chip to be
plugged into portable and/or fixed electronic devices. It allows a wide range of devices to
communicate with each other wirelessly.
How Bluetooth works?
Bluetooth was invented by L.M. Ericsson of Sweden in 1994, it is a cable-replacement
technology. A Bluetooth chip is a microcomputer chip, which is able to transmit or
receive a special radio frequency. For example, a mobile phone which contains a
Bluetooth chip can transmit an information to the electronic system in an automobile,
which has a built-in Bluetooth chip, in order to demand the automobile to lock up the
General applications of Bluetooth
Bluetooth offers wireless access to local area network (LAN), public switched telephone
network (PSTN), the mobile phone network and the Internet for a host of home
appliances and portable handheld interfaces. With Bluetooth, devices such as laptop
computers, handheld computers, cellular telephones, pagers, fax machines, and printers
can wirelessly communicate with each other.
Although the Bluetooth technology can overcome the limitations of the wired networks,
there is still room for further development before it is widely adopted.
BIOS Beep Codes
When a computer is first turned on, or rebooted, its BIOS performs a power-on self test
(POST) to test the system's hardware, checking to make sure that all of the system's
hardware components are working properly. Under normal circumstances, the POST will
display an error message; however, if the BIOS detects an error before it can access the
video card, or if there is a problem with the video card, it will produce a series of beeps,
and the pattern of the beeps indicates what kind of problem the BIOS has detected.
Because there are many brands of BIOS, there are no standard beep codes for every
BIOS. The two most-used brands are AMI (American Megatrends International) and
Phoenix. Below are listed the beep codes for AMI systems, and here are the beep codes
for Phoenix systems.
AMI Beep Codes
Beep Code Meaning
1 beep DRAM refresh failure. There is a problem in the system memory or the motherboard.
2 beeps Memory parity error. The parity circuit is not working properly.
3 beeps Base 64K RAM failure. There is a problem with the first 64K of system memory.
4 beeps System timer not operational. There is problem with the timer(s) that control functions on the
5 beeps Processor failure. The system CPU has failed.
6 beeps Gate A20/keyboard controller failure. The keyboard IC controller has failed, preventing gate
A20 from switching the processor to protect mode.
7 beeps Virtual mode exception error.
8 beeps Video memory error. The BIOS cannot write to the frame buffer memory on the video card.
9 beeps ROM checksum error. The BIOS ROM chip on the motherboard is likely faulty.
10 beeps CMOS checksum error. Something on the motherboard is causing an error when trying to
interact with the CMOS.
11 beeps Bad cache memory. An error in the level 2 cache memory.
1 long beep, 2 short Failure in the video system.
1 long beep, 3 short A failure has been detected in memory above 64K.
1 long beep, 8 short Display test failure.
Continuous beeping A problem with the memory or video.
Graphical User Interface (GUI)
a method of interacting with a computer through direct manipulation of graphical images
and widgets (graphical components or controls) in addition to text (using mouse and
keyboard). Examples of widgets:
• check box
• radio button
• combo box
• text box (edit field)
• status bar
A program interface that takes advantage of the computer's graphics capabilities to
make the program easier to use. Well-designed graphical user interfaces can free the
user from learning complex command languages. On the other hand, many users find
that they work more effectively with a command-driven interface, especially if they
already know the command language.
Graphical user interfaces, such as Microsoft Windows and the one used by the Apple
Macintosh, feature the following basic components:
pointer : A symbol that appears on the display screen and that you move to
select objects and commands. Usually, the pointer appears as a small angled
arrow. Text -processing applications, however, use an I-beam pointer that is
shaped like a capital I.
pointing device : A device, such as a mouse or trackball, that enables you to
select objects on the display screen.
icons : Small pictures that represent commands, files, or windows. By moving
the pointer to the icon and pressing a mouse button, you can execute a command
or convert the icon into a window. You can also move the icons around the
display screen as if they were real objects on your desk.
desktop : The area on the display screen where icons are grouped is often
referred to as the desktop because the icons are intended to represent real
objects on a real desktop.
windows: You can divide the screen into different areas. In each window, you
can run a different program or display a different file. You can move windows
around the display screen, and change their shape and size at will.
menus : Most graphical user interfaces let you execute commands by selecting a
choice from a menu.
The first graphical user interface was designed by Xerox Corporation's Palo Alto
Research Center in the 1970s, but it was not until the 1980s and the emergence of the
Apple Macintosh that graphical user interfaces became popular. One reason for their
slow acceptance was the fact that they require considerable CPU power and a high-
quality monitor, which until recently were prohibitively expensive.
In addition to their visual components, graphical user interfaces also make it easier to
move data from one application to another. A true GUI includes standard formats for
representing text and graphics. Because the formats are well-defined, different
programs that run under a common GUI can share data. This makes it possible, for
example, to copy a graph created by a spreadsheet program into a document created by
a word processor.
Many DOS programs include some features of GUIs, such as menus, but are not
graphics based. Such interfaces are sometimes called graphical character-based user
interfaces to distinguish them from true GUIs.
DOS (disk operating system)
most often refer to MS-DOS (Microsoft disk operating system). Originally developed by Microsoft
for IBM-compatible personal computers (PC).
DOS is a 16-bit operating system and does not support multiple users or multitasking.
CLI versus GUI
Command Line Interface (CLI) Graphical User Interface (GUI)
command line system with keyboard menu-driven system with icons
run in a character-cell text mode run in a pixel-based graphics mode
difficult to learn, not user friendly easy to learn, shorter learning path
users have to remember DOS commands no need to remember commands
user must have good knowledge of the
requires training and special skills requires less skills and training
suitable for experienced user suitable for inexperienced user
system requirement: simple computer
system with very little resources (CPU
speed, RAM, disk space, display resolution)
system requirement: require more computer
power (CPU speed, RAM, disk space,
display resolution and response, etc.)
Electronic junk mail or junk newsgroup postings. Some people define spam even more
generally as any unsolicited e-mail. However, if a long-lost brother finds your e-mail
address and sends you a message, this could hardly be called spam, even though it's
unsolicited. Real spam is generally e-mail advertising for some product sent to a mailing
list or newsgroup.
In addition to wasting people's time with unwanted e-mail, spam also eats up a lot of
network bandwidth. Consequently, there are many organizations, as well as individuals,
who have taken it upon themselves to fight spam with a variety of techniques. But
because the Internet is public, there is really little that can be done to prevent spam, just
as it is impossible to prevent junk mail. However, some online services have instituted
policies to prevent spammers from spamming their subscribers.
There is some debate about the source of the term, but the generally accepted version
is that it comes from the Monty Python song, "Spam spam spam spam, spam spam
spam spam, lovely spam, wonderful spam…" Like the song, spam is an endless
repetition of worthless text. Another school of thought maintains that it comes from the
computer group lab at the University of Southern California who gave it the name
because it has many of the same characteristics as the lunchmeat Spam:
Nobody wants it or ever asks for it.
No one ever eats it; it is the first item to be pushed to the side when eating the entree.
Sometimes it is actually tasty, like 1% of junk mail that is really useful to some people.
A slang term for a computer enthusiast, i.e., a person who enjoys learning programming
languages and computer systems and can often be considered an expert on the
subject(s). Among professional programmers, depending on how it used, the term can
be either complimentary or derogatory, although it is developing an increasingly
derogatory connotation. The pejorative sense of hacker is becoming more prominent
largely because the popular press has co-opted the term to refer to individuals who gain
unauthorized access to computer systems for the purpose of stealing and corrupting
data. Hackers, themselves, maintain that the proper term for such individuals is cracker.
(1) To break into a computer system. The term was coined in the mid-80s by hackers
who wanted to differentiate themselves from individuals whose sole purpose is to sneak
through security systems. Whereas crackers sole aim is to break into secure systems,
hackers are more interested in gaining knowledge about computer systems and possibly
using this knowledge for playful pranks. Although hackers still argue that there's a big
difference between what they do and what crackers do, the mass media has failed to
understand the distinction, so the two terms -- hack and crack -- are often used
(2) To copy commercial software illegally by breaking (cracking) the various copy-
protection and registration techniques being used.
• Processor management
• Memory management
• Device management
• Storage management
• Application interface
• User interface