Handheld and portable computers are small, lightweight computers that are designed to be operated while held by hand or from a desk or tabletop. They contain a processor, memory, I/O ports, and expansion slots. They also provide an operating system, user interface, and battery power. There are three basic types of handheld and portable computers. Tablet personal computers (PCs) are notebook computers that feature a liquid crystal display (LCD) on which users can write with a special pen called a stylus. Tablet PCs digitize handwriting and often include a keyboard or mouse. Personal digital assistants (PDAs) are smaller than tablet PCs, but also include a stylus or keyboard. Typically, PDAs function as a cellular phone, fax sender, Web browser, and personal organizer. They may also provide handwriting recognition and voice recognition technologies. Pocket PCs, a third type of handheld and portable computers, are advanced PDAs with low power processors, brilliant trans-reflective color screens, wireless communication features, and many add-on options. Pocket PCs have one or more expansion slots for added memory. 

Many handheld and portable computers include flat panel displays (FPDs) that use LCD or gas plasma technologies. In LCDs, an electric current passes through a liquid crystal solution that is trapped between two sheets of polarizing material. The crystals align themselves so that light cannot pass, producing an image on the screen. LCDs can be monochrome or color. Color displays can use a passive matrix or an active matrix . Passive matrix displays contain a grid of horizontal and vertical wires with an LCD element at each intersection. In active matrix displays, each pixel has a transistor that is switched directly on or off, improving response times. Unlike LCDs, gas plasma displays consist of an array of pixels, each of which contains red, blue, and green subpixels. In the plasma state, gas reacts with the subpixels to display the appropriate color. For both LCDs and gas plasma displays, resolutions include pixel measurements of 160 x 160, 320 x 240, 320 x 320, and 480 x 160. 

Handheld and portable computers are small, lightweight computers that are designed to be operated while held by hand or from a desk or tabletop. They contain a processor, memory, I/O ports, and expansion slots. They also provide an operating system, user interface, and battery power. There are three basic types of handheld and portable computers. Tablet personal computers (PCs) are notebook computers that feature a liquid crystal display (LCD) on which users can write with a special pen called a stylus. Tablet PCs digitize handwriting and often include a keyboard or mouse. Personal digital assistants (PDAs) are smaller than tablet PCs, but also include a stylus or keyboard. Typically, PDAs function as a cellular phone, fax sender, Web browser, and personal organizer. They may also provide handwriting recognition and voice recognition technologies. Pocket PCs, a third type of handheld and portable computers, are advanced PDAs with low power processors, brilliant trans-reflective color screens, wireless communication features, and many add-on options. Pocket PCs have one or more expansion slots for added memory. 

Many handheld and portable computers include flat panel displays (FPDs) that use LCD or gas plasma technologies. In LCDs, an electric current passes through a liquid crystal solution that is trapped between two sheets of polarizing material. The crystals align themselves so that light cannot pass, producing an image on the screen. LCDs can be monochrome or color. Color displays can use a passive matrix or an active matrix . Passive matrix displays contain a grid of horizontal and vertical wires with an LCD element at each intersection. In active matrix displays, each pixel has a transistor that is switched directly on or off, improving response times. Unlike LCDs, gas plasma displays consist of an array of pixels, each of which contains red, blue, and green subpixels. In the plasma state, gas reacts with the subpixels to display the appropriate color. For both LCDs and gas plasma displays, resolutions include pixel measurements of 160 x 160, 320 x 240, 320 x 320, and 480 x 160. 

Handheld and portable computers differ in terms of performance specifications, I/O ports, expansion slots, interface options, and communication features. Performance specifications include processor type, operating system type, and random access memory (RAM). I/O ports allow connections to peripherals such as mice, keyboards, infrared transceiver ports, modems, universal serial bus (USB) ports, Ethernet ports, and IEEE-1394 ports. Expansion slots use secure digital (SD) and secure digital input/output (SDIO) cards, as well as specialized boards such as multimedia cards (MMCs). Interface options for handheld and portable computers include color displays, built-in speakers, display backlighting, handwriting recognition, headset jacks, membrane keypad interfaces, tactile keyboard interfaces, touch screen options, voice recorders, and voice recognition. Communication features include integrated Bluetooth^®, wireless LAN (WLAN), and wireless fidelity (Wi-Fi^®) technologies. Bluetooth is a registered trademark of the Bluetooth Special Interest Group (SIG). Wi-Fi is a registered trademark of the Wi-Fi Alliance.