Form factors

Screen

Screen size, resolution and colours have been steadily improving in PDAs over the years. Expect 4000 colours and a screen resolution of 160x160 pixels in low-end models, with 65K and 320x480 pixels in the more expensive models that feature larger screens. Some models allows the screen to be used in either portrait or landscape, but this depends on the size and type of device and whether the operating system supports this functionality. It's a useful feature for web browsing and reading documents. Transflective screens are backlit for indoor use can absorb the sun's ray when outdoors, to ensure a readable screen in bright light. A TFT (thin film transistor) screen gives better resolution and brightness because each pixel is lit individually.

Size

The PDA market has diversified and there are a range of models to suit different needs, applications and budgets. Accordingly, form factors vary depending on the applications and power on board. Low-end models, designed to replicate a diary, tend to be lighter and smaller, but have smaller screens, less processing power and fewer applications. Models with large screens tend to be bigger and heavier, but have processing power and storage capacity for weeks out of the office.

Touchscreen vs Keypad

Some models use a touchscreen, while others have a keypad. Some devices also have one or two programmable buttons for quick access to regular tasks or commonly used applications. Models with a touchscreen need a stylus to activate the applications and input data. Some PDAs have handwriting recognition software, such as Palm Graffiti or Block Recognizer and Letter Recognizer for Windows devices, which requires learning some pre-set characters for data input. Transcriber, which runs on Windows devices, will attempt to read a user's own handwriting and convert it to text.

A device with both touchscreen and keypad offers the best functionality; however, it may come at the expense of reducing screen size and keypad size. Small keypads tends to be multi-press alphanumeric to save space, while larger devices have the space for a Qwerty-style keypad. A standalone keyboard, which plugs in or is wireless, is an option to speed up data entry in devices with only a touchscreen or small keypad.

Battery

The most common types of battery are Li-Ion (Lithium-Ion) and Li-Ion Polymer, a lighter variant used in compact devices because it can be shaped to fit the device. Battery life depends on many factors, such as type of battery and processor, as well as battery saving features like screen shut down. In general, a 1300mAh Li-Ion battery will give about four to 10 hours of talk time, and 200 to 300 hours standby time.