TO MY PREVIOUS SELF,
Before we start talking about the interconnections of computers I would to inform my previous self to floss your teeth a lot. If you floss your teeth they will not start wiggling later on in life. Now onward to computer technology at the end of 2007.
All computers everywhere will be connected together and will talk to each other on something called the giant worldwide web. From the user perspective, they will type in a request for a certain page – this will be called a URL. This stands for a Universal Resource Identifier. It originally stood for Universal Resource Locator, but not everything that a URL refers to is a locator. By the time this was observed, everybody was calling them URLs, so it stuck. In the twenty-first century everybody calls things by their first letters even when the terms change.
So, Mark, you will have a client with a software program called a browser. In this browser, you will type URLs like this one:
THis URL is divided into three parts:
1. The Protocol (http://)
2. The server name (markcole.wordpress.com)
3. The file name (mypage)
The browser then sends a GET request over the internet asking to GET the file name (3) from a server (2) using the http: protocol (1). It may also send something called a cookie, but we won’t discuss that here.
The server machine then sends a bunch of characters representing html code to your browser.
Your browser (the computer program on your machine) picks up the html code and converts the tags in the html code into a formatted page on your screen. It may also send a cookie in the header information. But we are not discussing cookies here!
The information is sent on something called the internet. But what is the internet?
It is a gigantic collection of millions of computers all linked by a computer network.
A home computer can be connected to the internet using a modem, dsl, cable modem, or a fiber optic cable (like my house) that talks to an Internet Service Provider (ISP). A business or school computer is linked in a LAN (local area network) using a T1 line – a T1 line can usually handle 1.5 million bits per second while a phone line can handle 30,000 to 50,000 bits per second. A good way to check your internet speed is to take an internet download or upload test like the one here. Here are the speeds that I got, measured in thousands of bytes per second:
|Server in:||Download (kbps) Berwynn PA at Noon 12.12.2007 Win XP||Upload (kbps) Berwynn PA at Noon 12.12.2007 Win XP|
You might try trying this test on your machine – but since you are using 20th century technology you will probably get slower speeds and the test will not exist yet.
ISPs then connect to larger ISPs which are all connected together by fiber-optic backbones, fiber-optic lines, under sea cables, and satellite links. There is a nice picture of an internet backbone here. http://en.wikipedia.org/wiki/Internet_backbone
How does the internet keep all this straight? IP Addresses
Every computer has a unique IP (internet protocol) address that looks like this:
You can find out your address by typing ipconfig in the Command Prompt window (if you have windows xp). On Unix this is nslookup. It is hard to remember numbers – so we also call servers by english names such as http://www.wordpress.com/
You access through a protocol such as the http protocol summarized nicely in The Original HTTP as defined in 1991.
That is enough for now. Armed with this information you should be able to be much more successful than me.
Mark from the twenty-first century