protocols

Why are protocols important for networking?

For devices across networks to talk to each other there must be a common language. Protocols and set rules for them allow vendors to produce machines that can talk from network to network.

404

HTTP 404

From Wikipedia, the free encyclopedia

HTTP

Persistence · Compression · HTTP Secure

Headers

ETag · Cookie · Referrer · Location

Status codes

301 Moved permanently

302 Found

303 See Other

403 Forbidden

404 Not Found

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The 404 or Not Found error message is a HTTP standard response code indicating that the client was able to communicate with the server but the server could not find what was requested. 404 errors should not be confused with "server not found" or similar errors, in which a connection to the destination server could not be made at all. Another similar error is "410: Gone", which indicates that the requested resource has been intentionally removed and will not be available again. A 404 error indicates that the requested resource may be available in the future.

Microprocessor

A microprocessor incorporates most or all of the functions of a central processing unit (CPU) on a single integrated circuit (IC).^[1] The first microprocessors emerged in the early 1970s and were used for electronic calculators, using binary-coded decimal (BCD) arithmetic on 4-bit words. Other embedded uses of 4- and 8-bit microprocessors, such as terminals, printers, various kinds of automation etc, followed rather quickly. Affordable 8-bit microprocessors with 16-bit addressing also led to the first general purpose microcomputers in the mid-1970s.

Bits, Bytes, Mega, Giga, Tera

Bits, Bytes, Mega, Giga, Tera

1 bit = a 1 or 0 (b)
4 bits = 1 nybble (?)
8 bits = 1 byte (B)
1024 bytes = 1 Kilobyte (KB)
1024 Kilobytes = 1 Megabyte (MB)
1024 Megabytes = 1 Gigabyte (GB)
1024 Gigabytes = 1 Terabyte (TB)

Common prefixes:
- kilo, meaning 1,000. (one thousand) 10^3 (Kilometer, 1,000 meters)
- mega, meaning 1,000,000. (one million) 10^6 (Megawatt, 1,000,000 watts)
- giga, meaning 1,000,000,000 (one billion) 10^9 (Gigawatt, 1,000,000,000 watts)
- tera, meaning 1,000,000,000,000 (one trillion) 10^12

The smallest amount of transfer is one bit. It holds the value of a 1, or a 0. (Binary coding). Eight of these 1's and zero's are called a byte.

Why eight? The earliest computers could only send 8 bits at a time, it was only natural to start writing code in sets of 8 bits. This came to be called a byte.

A bit is represented with a lowercase "b," whereas a byte is represented with an uppercase "b" (B). So Kb is kilobits, and KB is kilobytes. A kilobyte is eight times larger than a kilobit.

A simple 1 or 0, times eight of these 1's and 0's put together is a byte. The string of code: 10010101 is exactly one byte. So a small gif image, about 4 KB has about 4000 lines of 8 1's and 0's. Since there are 8 per line, that's over (4000 x 8) 32,000 1's and 0's just for a single gif image.

How many bytes are in a kilobyte (KB)? One may think it's 1000 bytes, but its really 1024. Why is this so? It turns out that our early computer engineers, who dealt with the tiniest amounts of storage, noticed that 2^10 (1024) was very close to 10^3 (1000); so based on the prefix kilo, for 1000, they created the KB. (You may have heard of kilometers (Km) which is 1000 meters). So in actuality, one KB is really 1024 bytes, not 1000. It's a small difference, but it adds up over a while.

The MB, or megabyte, mega meaning one million. Seems logical that one mega (million) byte would be 1,000,000 (one million) bytes. It's not however. One megabyte is 1024 x 1024 bytes. 1024 kilobytes is called one Megabyte. So one kilobyte is actually 1024 bytes, and 1024 of those is (1024 x 1024) 1048576 bytes. In short, one Megabyte is really 1,048,576 bytes.

There is a difference of about 48 KB, which is a decent amount. If you have a calculator, you will notice that there is actually a 47KB difference. There is a difference of 48,576 bytes, divided by 1024, and you get the amount of real kilobytes... 47.4375

All of this really comes into play when you deal with Gigabytes, or roughly one billion bytes. One real Gigabyte is actually 1024 bytes x 1024 bytes x 1024 bytes...1,073,741,824. However, most people like to simplify this by simply saying that one Gigabyte is only 1,000,000,000 (one billion) bytes; which makes sense because the prefix Giga means one billion.

References

• http://physics.nist.gov/cuu/Units/binary.html

ISPs

List of ISPs in India

From Wikipedia, the free encyclopedia

Internet service providers in India.

• 
  BSNL, state owned public sector company.
• Airtel
• Sify
• HFCL
• VSNL
• Reliance Communications
• Tata Teleservices
• Spice
• MTNL
• youtelecom

Generations of Computer

Sixth generation

This generation saw a move towards PC-like architectures in gaming consoles, as well as a shift towards using DVDs for game media. This brought games that were both longer and more visually appealing. Furthermore, this generation also saw experimentation with online console gaming and implementing both flash and hard drive storage for game data.

• Sega's Dreamcast released in North America on September 9, 1999 was the company's last video game console, and was the first of the generation's consoles to be discontinued. Sega implemented a special type of optical media called the GD-ROM. These discs were created in order to prevent software piracy, which had been more easily done with consoles of the previous generation; however, this format was soon cracked as well. It was discontinued in 2001, and Sega transitioned to software developing/publishing only. It also sported a 33.6Kb modem which could be used to access the internet or play some of the games, like Phantasy Star Online, online.
• Sony's PlayStation 2 was released in North America on October 26, 2000 as the follow-up to its highly successful PlayStation, and was also the first home game console to be able to play DVDs. As was done with the original PlayStation in 2000, Sony redesigned the console in 2004 into a smaller version. As of July 2008, 140 million PlayStation 2 units have been sold.^[7][8] This makes it the best selling console of all time to date.
• The Nintendo GameCube was Nintendo's fourth home video game console and the first console by the company to use optical media instead of cartridges. The Nintendo GameCube did not play standard 12 cm DVDs, instead employing smaller 8 cm optical discs.
• Microsoft's Xbox was the company's first video game console. The first console to employ a hard drive right out of the box to save games, and had similar hardware specifications to a low-end desktop computer at the time of its release. Though criticized for its bulky size, which was easily twice that of the competition, as well as for the awkwardness of the original controller that shipped with it, it eventually gained popularity due in part to the success of the Halo franchise.

VLSI

Very-large-scale integration (VLSI) is the process of creating integrated circuits by combining thousands of transistor-based circuits into a single chip. VLSI began in the 1970s when complex semiconductor andcommunication technologies were being developed. The microprocessor is a VLSI device. The term is no longer as common as it once was, as chips have increased in complexity into billions of transistors.