What Physicians Should Know About Clients and Servers

Clients and servers are part of the inner workings of practically every computer system that you use in your practice. Usually hidden from view, clients and servers can become something of direct concern to you when browsing the Web or trying to read your e-mail, or when they stop working. Most physicians are unaware of client-server architecture and its importance. This point was driven home to me recently by two, relatively computer-savvy physicians who asked me some questions about e-mail. You may also not be completely clear about how the various parts of an e-mail system fit together.

In computing, clients and servers are ubiquitous. The good news is that you already understand the basic idea, even if you don't realize it. In a restaurant, you are the client and your server is - you guessed it - the server. You submit requests to the server (ordering dinner) and the server receives your request. First they check its validity. If they are out of shrimp or you look penniless, they will respond with an error message. If the request is valid, the food is prepared and then the server completes your request by bringing the food to your table. That's it. Clients make requests, servers fulfill them.

As you know, computers aren't too bright. In a restaurant, the server may be able to read your mind or fill in the blanks if you make a poorly specified request but the computer can't. Therefore, every request to a computer server must adhere precisely to a protocol. In a sit-down restaurant, part of the protocol is to speak the language of the server or be good at charades. At P.F Chang's, you place your request at a counter and a server finds your table. At McDonald's, you request and pick up at the counter. These are three different restaurant protocols.

E-mail servers combine three functions: they receive and store mail your mail and they fulfill your requests to read mail and send mail. Each of these functions requires that the client (you or the application you are using) and the server speak the same protocol.

Sending mail uses SMTP (Simple Mail Transport Protocol). The advantage of using software (such as Thunderbird, Outlook, or a WebMail page) to perform the client functions on your behalf is that it negotiates the protocol for you and doesn't make any typos.

The take-home message is that the server does not know or care what client app you are using, or if you are using one at all. If the protocol is followed, the mail gets sent. When retrieving mail from a server, there are different protocols. The most common protocols are POP (Post Office Protocol) and IMAP (Internet Message Access Protocol).

When using POP, messages are first copied (downloaded) to whatever machine or device you are using to read the mail. You may opt to leave copies on the server or delete them as you read them. If you want to organize your old mail in folders, all of that happens on your computer.

If you access POP mail on multiple devices, you end up with multiple copies of each message, or different messages on each device, perhaps filed in different folders depending on your mood at the time.

IMAP leaves the mail on the server. When you read a message in your client app, the message is downloaded, displayed, and marked as read, but is not saved locally unless you choose to do so. If you create folders to organize saved messages, they are created on the server. Any device that you use to access mail will see the same folders and the same messages.

That's it. Any software designed to read and send mail can help you perform the client's responsibilities in an e-mail session. The vast majority of client apps support both POP and IMAP. Most e-mail servers, such as Microsoft Exchange, Novell GroupWise, and others support both POP and IMAP. Some services such as Earthlink and Time Warner Cable are apparently limited to POP.

So, it's your choice of client app and of protocol. POP is better if you only have one device and are using dial-up or are being charged per character for the amount of data transferred. Otherwise, IMAP is better as it avoids the confusion that invariably results when there are multiple copies of each message and when you can't remember which device you were using when you replied.

When you browse the Web, your browser is the client, someone's Web server is the server and the protocol is the Hypertext Transport Protocol (HTTP). You request a webpage. The server at the other end of the http://... fulfills it by sending you a page. If you start getting confused by a computer system that is misbehaving, the first step is to figure out who is the client and who is the server and if they are communicating.

Remember, whether it's mail, data, or the screen display itself, clients make requests, servers perform the actions necessary to fulfill requests, and they must agree on what language they are using to communicate.