USB

The Universal Serial Bus is the past, connecting devices to computers has been a real headache
Printers connected to parallel printer ports, and most computers only came with one. Things like Zip drives, which need a high-speed connection into the computer, would use the parallel port as well, often with limited success and not much speed.
Modems used the serial port, but so did some printers and a variety of odd things like Palm Pilots and digital cameras.
List of USB devices that you can buy today includes:
1. Network connections
2. Scanners
3. Mice
4. Joysticks
5. Printers
6. Webcams
7. Digital cameras
8. Scientific data acquisition devices
9. Modems
10. Telephones
11. Speakers
12. Video phones
13. Storage devices such as Zip drives

Modem

Modem (Modulator and Demodulator) is typically used to send digital data over a phone line. The sending modem converts digital data into analog data, which can be transmitted over telephone lines, and the receiving modem converts the analog data back into digital form. This is used to connect to Internet.
Modems are available in different capacities.
-300 bps - 1960s through 1983 or so
-1200 bps - Gained popularity in 1984 and 1985
-2400 bps
-9600 bps - First appeared in late 1990 and early 1991
-19.2 kilobits per second (Kbps)
-28.8 Kbps
-33.6 Kbps
-56 Kbps - Became the standard in 1998
-ADSL, with theoretical maximum of up to 8 megabits per second (Mbps) Gained popularity in 1999

Enhanced Parallel Port/Extended Capabilities Port

Enhanced Parallel Port (EPP) was created by Intel, Xircom and Zenith in 1991. EPP allows for much more data, 500 kilobytes to 2 megabytes, to be transferred each second. It was targeted specifically for non-printer devices that would attach to the parallel port, particularly storage devices that needed the highest possible transfer rate.
Close on the heels of the introduction of EPP, Microsoft and Hewlett Packard jointly announced a specification called Extended Capabilities Port (ECP) in 1992. While EPP was geared toward other devices, ECP was designed to provide improved speed and functionality for printers in 1994, the IEEE 1284 standard was released. It included the two specifications for parallel port devices, EPP and ECP. In order for them to work, both the operating system and the device must support the required specification. This is seldom a problem today since most computers support SPP, ECP and EPP and will detect which mode needs to be used, depending on the attached device. If you need to manually select a mode, you can do so through the BIOS on most computers.

Standard Parallel Port

The original specification for parallel ports was unidirectional, meaning that data only traveled in one direction for each pin. With the introduction of the PS/2 in 1987, IBM offered a new bidirectional parallel port design. This mode is commonly known as Standard Parallel Port (SPP) and has completely replaced the original design. Bidirectional communication allows each device to receive data as well as transmit it. Many devices use the eight pins (2 through 9) originally designated for data. Using the same eight pins limits communication to half-duplex, meaning that information can only travel in one direction at a time. But pins 18 through 25, originally just used as grounds, can be used as data pins also. This allows for full-duplex (both directions at the same time) ommunication.

Parallel Port Basics

Parallel ports were originally developed by IBM as a way to connect a printer to your PC. When IBM was in the process of designing the PC, the company wanted the computer to work with printers offered by Centronics, a top printer manufacturer at the time. IBM decided not to use the same port interface on the computer that Centronics used on the printer. It has 25-pin connector, a PC sends data to a printer or other device using a parallel port, it sends 8 bits of data (1 byte) at a time. These 8 bits are transmitted parallel to each other, as opposed to the same eight bits being transmitted serially (all in a single row) through a serial port. The standard parallel port is capable of sending 50 to 100 kilobytes of data per second.

How Parallel Ports Work?

If you have a printer connected to your computer, there is a good chance that it uses the parallel port. While USB is becoming increasingly popular, the parallel port is still a commonly used interface for printers. Parallel ports can be used to connect a host of popular computer peripherals:
-Printers
-Scanners
-CD burners
-External hard drives
-Iomega Zip removable drives
-Network adapters
-Tape backup drives