C H O O S I N G A M O D E M There are two kinds of modems--internal and external. INTERNAL MODEMS An internal modem is actually a modem and a serial port (COM port) built on a printed circuit card. This printed circuit card fits in a slot inside your computer on what is known as the mother board and uses the computer's power supply. The advantages of an internal modem are: 1. They are usually less expensive to buy. 2. They fit inside the computer and, therefore, don't take up extra desk space. 3. They contain both a modem and a COM port, so you don't need to purchase another COM port (called a serial card) if your computer doesn't have one available. The disadvantages of internal modems are: 1. They often are much harder to set up for the novice. 2. You are more likely to have conflicts with internal modems. My advice to beginners is to have a competent computer dealer (or local "guru") install an internal modem. EXTERNAL MODEMS External modems come housed in their own chassis and have their own power supply. The advantages of an external modem are: 1. They are easy to set up. All you do is plug in some cables and connect the modem to an existing serial port using a modem cable. Usually, COM1 is set up for your mouse, and COM2 is a good port for plugging in an external modem. 2. They don't take up a slot on your computer. 3. They will work with all kinds of computers, including desktop computers and laptops. 4. They are easy to move from one computer to another. 5. External modems have status lights that inform the user what is going on (if you have read your modem manual). 6. They have a speaker built-in, and most allow you to easily control the volume. You will need to know which COM port your modem uses when you install telecommunications software. Determining COM port usage is addressed later in this section. MODEM COMPATIBILITY Today, most modems are Hayes-compatible and this is what you will want. The majority of the almost outdated 2400 baud modems use a CCITT (Consultive Committee on International Telegraphy and Telephony) standard of V.22 bis. With a name like that you can see why they prefer to use an acronym. The faster 14,400 baud modems use V.32 bis/V.42 bis. The bis is a compression technology that packs data into a smaller space. MNP (Microcom Network Protocol) levels 1 through 4 and V.42 are error correction protocols. MNP 10 is an error correction protocol for use with cellular modems. For more about "V." terms, see the glossary of Telecommunication Terms. MODEM SPEED If you plan to use your modem for downloading lots of files, you will want to look at the faster modems with a baud rating of 14,400 bps or more. If a file takes one minute to transfer at 14,400 bps, it will take at least six minutes to transfer at 2400 bps. Actually, a modem can achieve a greater throughput than it's rated speed when you consider data compression. Throughput is the rate of useful data sent--considering data compression. A modem with data compression (V.42 or V.42 bis) should be set for a terminal speed of four times the modem's rated connect speed. That means a 14,400 bps modem should be set to 57,600 baud. A 14,400 bps modem under ideal circumstances can achieve a throughput rate of 57,600 bps, resulting in much greater efficiency. To achieve this, the auto-baud option must be turned off in your modem software. Turning the auto-baud feature off effectively locks the port speed to what you set it for in the modem software. This is sometimes referred to as "locking the port speed." The prices on faster modems have fallen dramatically in the last year. You can now buy a 14,400 bps modem with built-in fax capability for considerably less than $70.00 (at discount stores). Some of the new modems can be upgraded using software. If you buy a high speed modem and want to transfer data faster than 19,200 bps, you will need a special 16550- compatible UART chip in your serial port. A fast internal modem will already have such a chip built-in. If you have a fast external modem, you can purchase a serial card with a buffered 16550 UART chip for around $50.00 from your favorite super computer store. The latest in fast modems are called V.34. These modems support a baud rate of 28,800 bps. Many of these faster modems support a built-in fax, caller ID, and voice mail! The newer V.34 modems require a specially equipped serial card to handle the high speed data flow. An internal modem already has such features built in. Hayes is offering an Enhanced Serial Port card, equipped with a buffered UART 16550 chip, a coprocessor, and more memory, to handle their new line of super fast external modems. TIP If your modem has MNP 5, you may want to turn it off when downloading a compressed file. MNP 5 is a data compression protocol. The MNP 5 protocol does not recognize data that is compressed (for example a .ZIPped file), so it wastes time trying to compress data that is already compressed. This can really slow down a download. To turn off MNP 5, you will need to consult your modem manual. The V.42 bis does recognize compressed data, so there is no need to turn V.42 bis off. =========================================================