PDA Buyer's Guide - Page 3

Display Types

The types of displays used in handhelds are smaller versions of those used in notebook computers. Because handhelds are small, the display usually covers most of the front of the unit, so it's the most visible feature. It's important to have a display that's as bright and legible as possible on a handheld that is within your budget.

A typical palm-size handheld has a resolution of 320 x 240 pixels with four shades of gray; more expensive color models can offer more than 65,000 colors. Nearly all handhelds have a liquid crystal display (LCD), backlit touch-screen with a stylus for tapping commands, selecting items, and writing text.

Monochrome LCD is the least expensive and most energy-efficient choice, providing grayscale images and text.

Passive-matrix is a type of LCD color display on mid-level units that provides good color images when you view it straight on. There are three types of passive-matrix displays: double-layer supertwist nematic (DSTN), color super-twist nematic (CSTN), and High-Performance Addressing (HPA). Recent improvements in CSTN make it a great low-cost alternative to active-matrix.

Active-matrix, also called "thin film transistor" (TFT), is the brightest, sharpest, clearest, and most expensive type of LCD flat panel display that is practical for handhelds.

PDA Memory

All those great applications and all your important data are stored in RAM. Handhelds normally ship with 512 KB of system RAM in credit card models and up to 32 MB in larger models, often with an option for ordering more. Some models also provide expansion slots for more memory.

The operating system and built-in application programs are stored in ROM. For upgrading purposes, some manufacturers place the operating system in a socketed ROM module--a module you can remove from its socket and replace with a new one. Other manufacturers use flash memory--a type of memory that can be erased and reprogrammed but that doesn't erase when the power is disconnected.

Some handhelds include slots for CompactFlash cards. These 50-pin cards are similar in function to, but much smaller than, the 68-pin PCMCIA PC cards that are so popular in laptop and notebook computers. CompactFlash cards provide up to 96 MB (and growing) of data storage, but their small, light, energy-efficient design make them ideal for handhelds. (With an appropriate 50-to-68 pin adapter, a CompactFlash card can be used in a PCMCIA Type II slot.) There are two types of CompactFlash cards. Type I cards are 3.3mm thick, and Type II cards (also called CompactFlash Plus or CF+) are 5mm thick. Type II slots accept both Type I and Type II cards.

Finally, some larger handheld handhelds include PCMCIA slots for PCMCIA cards. There are three types of PCMCIA cards and slots: Type I, Type II, and Type III.

Type I cards are 3.3 millimeters thick and are used mostly as additional ROM or RAM. Type II cards are 5.5 millimeters thick and used mostly as modems. Type III cards are 10.5 millimeters thick and used mostly as virtual disk drives; however, most handhelds are not large enough to accommodate these.

A Type I slot holds one Type I card; a Type II slot holds one Type II card or two Type I cards. A Type III slot holds one Type III card or one Type I and one Type II card.

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Note: This buying guide is courtesy of Amazon.com and was written by Mike Brown, a consumer electronics editor for Amazon.com, covering phones, PDAs, printers, scanners, and other products.