Broadband For Dummies

The target audience for this primer is the vast majority of computer users; namely, people who are mystified by computers, email, Windows, and the web, and who are concerned about computer viruses and malware and hackers. You are welcome to download it, edit it, and give it to your friends and family who are using (or wish to use) a high-speed connection to the internet.

Especially if you are using a computer with Windows, and to a lesser extent if you are using another operating system (such as Apple OS X), you need to be aware that the internet is a dangerous place and your computer is at risk, both from within (e.g., from the Microsoft software) and from without. The threats from the outside are well-known: hackers getting into your computer; viruses and worms sent to you by email or accidentally downloaded from web sites; malicious "adware" and "spyware," generically known as "malware," which, when downloaded from web sites, will essentially take over your computer; and "phishing" scams set up by con artists to fool you into giving personal information so that they can steal your money. The danger from within is due to the fact that the bad guys have designed their invasive programs to take advantage of security flaws in the software. If you're going to spend any time in this environment, you will need a survival manual to keep you safe.

This primer is that manual. It is intended to do four things:

1. Give you a broad overview of what the web and email are about.
2. Give you a model so that you can understand the different ways that web and email services are provided.
3. Give you some terminology so that you won't be confused by "experts" who only know how to configure Microsoft Windows.
4. Give a simple, safe, reliable, and minimal approach to obtaining web and email internet services.

The internet is the basic backbone on which everything happens. Contrary to well-known claims, Al Gore did not invent it. It was invented with funding from ARPA in the 1960s, and improved in the 1970s at various research labs, including the Xerox Palo Alto Research Center, BBN (Bolt, Baranek and Newman) and Stanford University. The internet consists of computers that are connected together, each with a unique "internet address," which is a series of four numbers, each less than 256 and separated by a dot, such as 63.173.212.3. Programs were written so that computers could connect to each other, using their internet (IP) addresses. Two of the most important of these programs are ftp and telnet. ftp stands for "file transfer protocol"; it lets you tell some computer to transfer files to another one. telnet gives you a little terminal on your computer so that you can log in over the internet and work on another computer. Both are still in widespread use today.

Some computers on the internet have special jobs. For example, there are computers whose job is to route the data, which is sent in little packets of information, from one machine to another, typically going through many machines on the way. Some of these run DNS (Domain Name Service), which just translates "domain names", such as www.wyom.net, into the corresponding four number internet address.

Scientists collaborating at different locations and using different machines needed better ways to transfer data, images and text. In 1991, Tim Berners-Lee at CERN (the European high-energy particle physics consortium in Geneva) invented one of the two most important applications on the internet: the World Wide Web (a.k.a. "WWW" or "Web"). There were three key ideas:

1. A unique address for every chunk of information, so that it can be "downloaded" on request. This unique address is just a name, called a "URL" (universal request locator). It is a "link" to a "page" somewhere on the Web, and it is the name you type in the "Location" field of your browser to go to that page.
2. A simple language for formatting documents, such as this one, and embedding URL links. The language is called "html". It is text with some embedded instructions, such as specifying that some text is italicized or giving links to images or other web pages. The browser is a program that runs on your computer, which can display documents formatted in html.
3. A protocol for sending data between computers that lets you download web pages and forms, and also lets you upload data in forms that you have filled out. This protocol is called "http," which you may have seen in web addresses such as http://www.wyom.net. Browsers today assume the protocol is http, and also will fill in the "www", so you only need to specify wyom.net in the address window of your browser.

What do we mean by "download" and "upload"? The computers on the Web are not all "equal." Some are servers and the rest are clients. A server is a computer that will serve web pages to your computer when you ask for them. You computer is the client. When you go to www.google.com, the server at Google sends your web browser a page, which is actually a form. (It is a form because you can type text that can be uploaded back to the server.) Your browser downloads this page; you then type a query in a window, and upload the data back to Google's servers. These servers then find a set of URLs (links) that match your query, and send your browser (i.e., download to your browser) a new page, listing them. When you click on a link, your browser uploads the data associated with the request to the server that is holding it. There is enough information in the link so that your browser knows both the name of the server and the name of the specific piece of data, such as a photograph or article that you are requesting. The server could be anywhere on the planet, and it then downloads the requested page to your browser, which displays it in a (hopefully) readable format on your screen.

Berners-Lee also made a simple browser, but the first modern browser that displays images and marked-up text was made by a couple of people in Illinois who went on to found Netscape in 1994. The browsers we use today, such as Internet Explorer, Firefox, Safari and Google Chrome, are all descended from these first Netscape browsers.

Your ISP provides you with a number of mail boxes, each with a unique name of your choosing. Most ISPs provide two ways for you to get your email. The typical way is using a client email program, which they may provide. This program will download incoming mail from their server onto your computer, usually into a "folder" called "inbox." The email is downloaded from the server to your local machine automatically.

But suppose you are traveling and you don't have your computer. You can still read your email using the browser on any other computer that is connected to the internet. How? Your ISP provides a web address (like wyom.net) where you can log in and view and delete your mail. This web interface is different from your email client in an important respect: when you use a browser to view your email, it stays on the server. This would be a convenient alternative, except for one big problem: the program that your ISP provides for reading email from their server is lousy. You can use it in an emergency, but it is not a pleasant experience.

Google's Gmail solves this problem. It's a free web service that delivers your mail through your browser and keeps a copy on the server so that you have access to it any time and from any computer connected to the internet. With gmail, you don't need to have an email client on your machine. We'll discuss this in more detail later.

So the web and email are the two main reasons most people need a connection to the internet. But how do you get this connection?

Over 10 years ago, AOL and several other ISPs started a business that provided (1) internet connectivity over your telephone line (dial-up using a modem) and (2) a mailbox for your email. At that time, there were few alternatives.

But everything has changed since 1995. Today, most people can get a high-speed internet connection, also called broadband, in at least one of several ways. Download speeds are typically between 1 and 15 megabit/sec, which is many times faster than the 33.6 kilobit/sec rate of the modems. This factor of 30 to 500 is very important: among other things, it allows you to use graphical programs like Google Maps and Google Satellite interactively with fast response. Broadband can be delivered by:

1. DSL. This is a connection over your telephone line, that does not interfere with simultaneous use of the same line for voice and fax. It is typically provided by your local telephone company. It is limited in distance to about 2.5 miles from the origin of your "local loop" copper wire line to your telephone.
2. Cable. This is a connection over your cable line. Cable started with analog video service, then went to digital video (though you can still get analog video and should consider it because it is much cheaper), and many cable companies are now offering internet connectivity.
3. Dish. This is done with a direct line-of-sight microwave connection between the ISPs transceiver dish and a dish on your house.

Given the general availability of high-speed connections, what is the business model of AOL? Very simple: keep their 60 million or so accounts, bringing in $20/month each. But if you get broadband through your cable company, for example, and they give you more email accounts than you can use, why would you still pay AOL $20/month? AOL is no longer providing your internet connection, which was in any event abysmally slow. Sure, your friends know your email address at aol.com, and the lousy email client that AOL provides you is purposely crippled so that you can't export your address lists, if you've made them, to another email program. But that's a minor inconvenience. Here's the salient fact: once you have broadband, you have no use whatsoever for your previous dial-up ISP account. You should never need to use a klunky dial-up modem again!

In California, high-speed internet connection is about $40/month, through either DSL or Cable. Competition is slowly lowering the rates.

1. Router. The little box sets up a private little internet for your computer. It automatically assigns addresses and handles the forwarding of data from your computer to the real internet, and v.v. It also allows any computers on your little internet, called a Local Area Network (LAN), to talk to each other.
2. Firewall. Because you are going to have an always-on connection, you must guard against hackers running programs to try to break into your computer. The little box will prevent this. To the outside world, absolutely nothing is visible behind this box.
3. Switch. It typically has 4 internet plugs, called "ports," to allow you to plug in up to 4 computers or network devices. The switch is what physically allows the data to go into any port and out of any other port.

This little box can be purchased for between $20 and $50, and we can call it, as you might imagine, a router/firewall/4-port switch. There are several good brands. Be sure you get one that has wireless ethernet connectivity to your computers (as well as wired connectivity from the 4 ports). From here on I'm going to call the little box a "router," but keep in mind that it has several important functions, of which being a router is just one.

When you get Cable or DSL internet, you will need a high-speed modem. If they are going to charge you a monthly rental, it's usually cheaper to buy it. The input to this modem is your telephone line or your cable, and the output from the modem is an internet cable, which you can attach directly to your computer. But don't do that! There are many reasons not to connect your computer directly to the modem, and you already know one: you need a firewall. So you are going to get a router (which might be supplied free by your ISP), and the output of the modem goes into the router. This router will then talk to your computers (and printers), either through a wired connection or, most commonly now, wirelessly. (FYI, the wired connections are made by a special internet cable has connector jacks that look like wide telephone jacks. They have 8 wires, of which only 4 are typically used.)

Here's another reason to use the router. When you get a DSL modem, you will be given some software to install on your PC. SBC calls it "Enternet-100". This software is required to let your computer talk directly to the outside internet, but only if you don't have a router. With the router, all those functions are automatically taken care of, and you must not install any software from your broadband ISP. Repeat: Do not install any software from your broadband internet service provider! This is good: life gets simpler.

Actually it gets very much simpler. As I said, you plug your cable or DSL modem into your router. With a wireless connection, when you start your computer, it will automatically find the router, and once you sign in (wireless should always require a password; otherwise, your neighbors can use your connectin), your computer will automatically connect. With a wired connection, no password is required -- when your computer boots up, it will be connected to the internet (through the router and the modem).

If this is the first time you are turning on a computer, you will be asked a few questions by a "setup wizard", such as the name of the computer and the type of internet connection. For the latter, keep in mind that:

• You are connecting to the internet by a fast connection, not with a dial-up connection.
• Your local internet address (remember, those four-number-separated-by-dot things?) will be assigned automatically. You never need to know it.

The router itself will need to be configured to work with your ISP. They will do this for you when they install your internet service. The router will almost always be configured to assign a local IP address to each of your computers (or network devices) as they are turned on. This dynamic configuration is called "DHCP".

Another important advantage of using a router with firewall is that you don't need to put special firewall software on your computer. This is not just a matter of convenience. In fact, it is important to avoid using all firewall software on your computer. This software, which you can get from various sources, the most notorious being ZoneAlarm, interacts badly with your most important internet programs; namely, your browser, your email and your anti-virus software. Norton and McAfee will try to sell you firewall software for your computer. Avoid it. Not using any firewall software will make your computer much easier to use.

Your router also has a web server built in, so you can see and change the settings using your browser. But as I said before, you shouldn't need to do this, because it will come configured to automatically handle your internet connection with maximum safety. (If you are curious, the typical local address of your router is 192.168.1.1, and you can go to your router by typing that into the address field of your browser. It will then display menus, such as the addresses of all the computers it is managing on the local area net. The local address it assigns your computer will be something like 192.168.1.100).

Viruses are pieces of code or programs that, when executed, can replicate themselves and send copies over the internet to other computers. Spyware is software, usually advertising-related, that is downloaded and sends information to another computer about what you are doing on your computer. Some spyware, which is also called adware, pops up annoying windows on your computer. Most spyware/adware has been so poorly designed that it essentially takes over the functioning of your computer, absorbing most of the computation cycles and slowing the computer to a crawl whenever you ask it to do something. Destructive variants of spyware, called "malware," overwrite minor system files and capture and send sensitive information, such as credit card numbers. You don't want to have any of this on your computer!

If you have an Apple, you probably don't need to worry about viruses, because there are (relatively) few Apple computers and, more importantly, the Apple operating system is much more secure than Windows. This is particularly true for Apple's newer Unix operating system, OSX. Linux and other variants of Unix are, so far, safe from all the common viruses.

Likewise, spyware mostly affects Windows computers. It has no effect on Unix. With Windows, the likelihood of infection is higher for two reasons: (1) the Microsoft Internet Explorer has a utility called ActiveX (a way of downloading and running programs, with insufficient security), and (2) the actual malware is tailored to run on Windows. So the rest of this section is for people using Windows on PCs. If you're running Apple OSX or Linux, you can skip the rest of this secdtion, unless you want to find out how much "fun" you are missing by using a relatively secure computer.

If you have a PC running Windows, there are several things that you should do to keep your computer "healthy." The most important is to install Norton Anti-Virus, which costs about $30. Once installed, Norton will automatically update itself periodically when you are connected to the internet. It will do this for one year after you purchase it, and you should renew the "subscription" each year. Norton will catch and isolate nearly every virus that comes to you as a mail attachment. But just get anti-virus from Norton.

By no means should you get McAfee's anti-virus software. McAfee is much more difficult to use than Norton, and it has been known to behave badly with other internet applications.

If for some reason you insist on using IE, be sure to turn off Microsoft's ActiveX software on the Internet Explorer (IE) browser, including all ActiveX "scripting" options. You'll find the ability to do this under the "Control Panel" and "Security". ActiveX allows someone to run programs on your computer, and these programs can be attached to email or downloaded from web sites by your browser. It is very dangerous. If you turn it off, a very small number of web sites will not work properly, but this is a small price to pay for the safety you get in exchange.

You should get in the habit of not opening email attachments about which you have any suspicions. Norton will catch most viruses, but it is best to stay alert. Viruses have become very sophisticated, and once they get in someone's computer, they will propagate by sending mail to everyone in that person's email contact list.

OK. We've established that there are three programs you must have if you are to use the internet. The first is a web browser, the second is an email client (although you can also use the web browser to get email), and the third is Norton Anti-Virus. In this section we discuss the browser, and in the next, your email client program.

As mentioned above, because of the security problems associated with the Microsoft IE browser, I recommend that the very first thing you do with IE is download Google Chrome, and then never use IE again. After the Chrome browser is downloaded, delete the IE shortcut icon so that you don't accidentally start it up. Check out the various functions available by clicking on the little wrench icon in the upper right corner. Security updates in the browser will be automatically downloaded to your computer, so you don't need to worry about keeping the version of Chrome up-to-date.

Here's a real-life case. A friend of mine is an author, and she uses her computer ("Computer 1") for her writing. She wants maximum safety: reliable backup in case of hardware failure, no spyware to compromise Windows, no break-in from the internet. The works. She also needs to use email and e-commerce, and is willing to get a second computer ("Computer 2") to perform that function.

A consultant suggested that she completely isolate Computer 1, and burn CDs for backup and to transfer manuscripts to Computer 2. However, burning CDs is tricky and may be near the limit of my friend's ability to do it reliably.

Fortunately, there a simpler and more reliable way to meet her needs. Connect both computers to the internet through a router (with firewall and 4-port switch), with the firewall settings as they come from the manufacturer: all incoming ports closed. (You can only receive packets from outside the firewall from a server to which you have first established a connection, such as a web server at Google or Amazon.) We have covered this earlier -- no hacker can break through such a firewall. To meet the other two requirements, my friend gets a GMail account and sets her home page on Computer 1 to http://www.gmail.com. When going through the firewall to the internet, Computer 1 only goes to this page. Using Firefox, of course.

Then she uses her GMail account for exactly two functions: backup and communication with Computer 2. For backup, she attaches a chapter (or some other unit) to an email, and sends it to herself. The result is that the attachment is stored on Google's GMail server. This is a completely reliable method for backup, By contrast, if you burn a CD, it can get lost, destroyed, stolen, or be defective. Once the email has been sent, Computer 2 can retrieve it, and then send it through her ISP email account (e.g., sbcglobal) account to the outside world. The beauty of this method is that the GMail account is completely private. The only traffic to and from this account is hers.

She can also use a second GMail account, as the connection from Computer 2 to the outside world. This second GMail account is "public," in that it is used to send and receive email to the outside world. Then, when she backs up a chapter, she does it by attaching the chapter to a GMail send message on Computer 1, and sends it to both of her GMail account addresses (the secret one, and the public one). Computer 2 then uses the public GMail account to forward the data to the outside world. Computer 1 is completely isolated from the internet, except for the secret GMail account.

Why have these two accounts? If she used GMail to send directly from Computer 1 to the outside, people outside would find out about the secret GMail account (so it would no longer be "secret"), and they would send email back to it. Eventually viruses and other boolean pathogens may find their way to her secret GMail account. So the safest procedure is to completely quarantine the GMail account. With a secure (un-guessable) password, it would then have a level of security close to what can be achieved with physical isolation.

Used in this way, Computer 1 will not even require anti-virus protection. Computer 2, which is really out there on the internet, should have Norton anti-virus. If she uses an ISP email account, it will certainly receive spam, perhaps in part because her ISP email address was sold to bad guys, or a computer somewhere that has her email address in an address book was turned into a spam-mailing zombie, or some other nasty scenario. But even if Computer 2 is disabled by spyware, Computer 1 remains completely safe, along with all the backups on the GMail server.

Today, wireless networking in the home has become ubiquitous. All computers you get today are wireless. Many devices, such as printers, tablets and smart phones, have wireless internet connectivity. You can stream internet wirelessly to your HDTV using a $50 device. So it is important that your router is able to broadcast wirelessly. If your ISP brings you internet through cable or dish, they are likely to give you a wireless router by default. If not, ask for it. If your ISP is your phone company, your internet will come through DSL, and they may not provide a router. Wireless routers are not appreciably more expensive than routers that don't have it. All wireless routers also have wired connections, which can also be used.

Wireless has a limited range, so if your router is not "visible" everywhere in your house, you can get a wireless "repeater" or "range extender". You run an internet cable from your router to this repeater, and it talks to all devices within its range.

Your goal is to have a problem-free setup using the best application software for the most important applications, and at the lowest cost. We've outlined how you can do this for the most generally useful and important applications (the web and email). Once you have a satisfactory computer, there are only three steps:

1. Get a high-speed (broadband) internet service, either DSL or Cable or Dish, which is "always on."
2. Get an inexpensive little wireless router (with firewall and 4-port switch), that will keep out hackers, save you from the misery of using software firewalls, handle all facets of your internet connection to your ISP so that you don't have to install any special software on your computers, and provide interconnectivity between computers and printers in your home or business.
3. Get a GMail account from Google and use it with your Google Chrome browser.

And if you have a dialup ISP, removing it will save you half the cost of your broadband connection.

• TLA. Three (or Two) Letter Acronym.
• FLA. Four (or Five) Letter Acronym.
• XP. Microsoft's old OS (operating system), Windows XP. It is nearly 10 years old now; don't use it.
• Vista. Microsoft's penultimate OS, released in 2007. A complete flop -- bloated and slow. People refused to use it, sticking with XP.
• Windows 7. Microsoft's newest OS. By far the best, relatively stable and easy to use. Still bloated, requiring 3 GB of RAM, and a bit slow, but much better than XP and Vista.
• ARPA. Advanced Projects Research Agency, a forward-looking organization funded by the Dept. of Defense, that was instrumental in laying the technical foundation for the internet. It was later renamed DARPA, to emphasize the military origin of the funding.
• IP. Internet Protocol. A low level description of how to route packets of data between machines on the internet. The IP address is a unique number for any machine that is connected to the internet.
• DNS. Domain Name Service. This is a program that is run by many machines on the intenet; it looks up IP addresses from domain names.
• FTP. File Transfer Protocol, by which two programs running on different machines allow you to move files from either one to the other.
• WWW. World Wide Web. The "web" of interlinked computers and data, that we use to "navigate", find information, and upload information for electronic commerce. The Web is one of the two killer apps enabled by the internet (the other being email).
• URL. Universal Resource Locator. A name given to some data on the web (a web page, a photograph, a music or video file, etc), that enables your web browser ("client") to tell the server that handles this data that you want it downloaded to you. The name should be unique. For example, this web page has the URL: http://www.leptonica.com/broadband.html. You can omit the "http://www." part, which is assumed by default.
• ISP. Internet Service Provider. The company that gives you access to the internet, and also provides you with email accounts. This used to be AOL, in the bad old days of dialup modems. Today, your ISP might be your telephone compnay (e.g., sbcglobal.net, providing DSL), your cable company (e.g., bresnan.com), a company that uses wireless microwave transmission (e.g., compunet.com), or if you have not yet upgraded to the 21st century, AOL or earthlink.
• DSL. Digital Subscriber Loop. Gives you digital data at about 1 Mbit/sec download and between 128 and 384 Kbit/sec upload), over your telephone line. Nobody every remembers what the initials "DSL" stand for.
• POP. Post Office Protocol. A protocol for handling your incoming email. The email is downloaded to your machine, and removed from the server, just like a letter that is delivered by the post office.
• IMAP. Internet Message Access Protocol. Another protocol for handling your incoming email. The email is downloaded to your email program, but a copy is saved on the server. Likewise, when you send email, a copy of your message is kept on the server. You can also store local copies, which can be useful for reading and composing messages when your are not on-line (i.e., not connected to your email servers).
• SMTP. Simple Mail Transfer Protocol. A protocol for handling your outgoing mail. This typically uses a different server than the one handling your incoming mail. Your ISP provides your email accounts and the servers that handle email. If you use an email program on your computer, such as Eudora, you need to know the names of both your POP and SMTP mail servers, so that Eudora knows where to look to receive email, and where to send email. Once your outgoing mail has been sent to the SMTP server, that server then sends it out onto the internet, where it is routed in several machine-to-machine hops to the recipient that you specified.
• LAN. Local Area Network. Your router will set up a LAN, assign addresses to all computers and other network devices that are attached to it, and transfer packets between the internet and the LAN. It will route data from the internet to the correct computer on the LAN, and it typically does this in an automatic fashion, using DHCP, so that you aren't aware of what local address is assigned.
• DHCP. Dynamic Host Configuration Protocol. One method that your router uses to assign local email addresses to your computer ("host").
• IE. Internet Explorer. Microsoft's bloated and relatively dangerous (security-wise) internet browser. It comes with your XP operating system, but you can download and use safer browsers, such as Firefox.
• JPEG. Joint Photographic Experts Group. You don't need to know that! It's a standard file format for compressing (usually color) images. Typical compression is about 15-20x over the size of the uncompressed image, which has 24 bits for each pixel (8 bits each of red, green, blue). Thus, the jpeg compressed image only stores about 1.5 bits of data for each color pixel. There is a new standard, called JPEG2000, which can use compression methods than standard jpeg (namely, wavelets instead of cosine transforms), but it is not yet in widespread use. It will give you the same picture quality with less than 1 bit of data for each set of red/green/blue pixels.

You can see how much memory you have by clicking on "System" in the Control Panel. In 2000, a computer with 128 MB of memory could squeak along running Windows 98. When XP came out, you needed at least 512 MB, and preferably 2 GB. If you don't have enough memory, it will take forever to boot up, and you'll hear the disk drive wildly seeking data to read. What is going on?

Ancient history. Computers before 1975 or so had a relatively small amount of memory, and they would typically run one program at a time. (The operating system was very small.) If your program didn't fit into the available memory, you needed to divide it up into pieces and tell the computer when to use each piece. But typically the operating system would read your program from disk into memory, and run it there. If your program was hogging the machine and another program couldn't fit in with it, the operating system would swap your program out and swap the other program in. In 1979, I remember watching an Interdata 8-32 computer, which cost about $250,000 and had only 4 MB of memory, swapping two programs that were compiling fortran. Each time a program would read in one line of source code to be compiled, it would get swapped out. The effect was comical -- that is, if you weren't waiting for your program to be compiled. In the late 1970s, virtual memory was implemented on Unix and other computers. Because it usually isn't necessary to have your entire program in memory at any time, the idea was to load only the parts of your program that were necessary into memory. The rest would stay on disk. The program was divided into pages, perhaps about 4 KB each, and they would be paged in when needed. Memory was a scarce resource, and this was a much more efficient use of memory. So typically your program would consist of some pages in memory and the other pages on the disk.

This isn't an ideal situation, because access to data on disk now takes about 5 milliseconds, whereas access to data in memory takes a few nanoseconds (a nanosecond is a thousandth of a millionth of a second). Thus, random access in memory can be up to a million times faster than finding something on the disk!

Your Microsoft OS (and all other operating systems) still have virtual memory -- they still page programs and data from the disk into RAM as needed. This is usually a good thing. If you have enough memory, a program gets loaded into memory, runs, and leaves. But if you don't have enough memory for all the programs you are loading to run (the OS itself, a browser, Norton, etc), chaos will ensue. To bring up the web browser, parts of the OS will get paged out. If too little of the OS is resident in memory, you get a situation where little pieces continually need to get paged back in, and other things are tossed out, as everything is fighting for memory. Disk paging is so slow that your computer essentially grinds to a halt.

My guideline is to have a minimum of 2 GB of memory for XP and 3 GB for Windows 7. You can live with less, but everything is significantly slowed down. And you really need this much memory for programs that make heavy use of images, such as Google Earth. With enough memory, everything will speed up on your computer: booting, logging in and out, and launching programs. It will allow you to run many different programs (such as email, several browsers, a DVD movie, and a text editor) simultaneously. It will greatly reduce wear and tear on your hard drive. And it will allow you to store a lot of images in memory and run great programs like Google Earth without annoying delays due to memory paging.