Personal Digital Assistants

Personal Digital Assistants

Personal Digital Assistants (PDAs) first appeared on the market in the form of electronic organizers. Organization remains their primary function; other features have been added as demand changes. The most basic organizers, often termed PIMs (Personal Information Managers), include a calendar, an address book, and a primitive notepad. PDAs serve as organizers almost without exception. The Franklin Day-Planners of old have been replaced with this new electronic way of managing personal information. Most PDAs also have the capability to synchronize with a PC, whether to upload or download information from a proprietary application for storage and backup purposes or to synchronize with popular PC organizers such as Microsoft Outlook or Lotus Organizer. This enables users to avoid the hassle of maintaining both paper and electronic versions of business or personal contacts, meetings, or appointments.

The ability to tote these PDAs anywhere you go makes them mobile, but not necessarily wireless. The ability to connect without docking with a PC makes a PDA wireless. The devices we cover in this chapter are wireless, whether inherently so or enabled via an add-on such as a wireless modem. More recently, PDA vendors are offering add-ons to bolster functionality. These additional components can play music, add memory, function as a modem, or add storage space.

Memory expansion is an attractive feature in many PDAs. Memory that is added to a mobile device is called flash memory. It can be programmed and erased repeatedly and consumes power only when accessed. Obviously, this is an important feature for devices with constrained battery power. Flash memory also retains its information after it is turned off. Memory upgrades are proportional to their size. Flash memory extensions the size of a postage stamp typically add 8MB of memory to a device, but larger format extensions can accommodate more than 64MB of memory. The catch is that, when adding 64MB of memory, the cost of the extension flash memory can sometimes exceed the cost of the PDA itself. See Table 4.1 for the sizes of various memory cards.

Table 4.1. Memory Card Sizes
Card	Size (mm3)
Springboard	23,085
PC card	14,552
CompactFlash	7,740
Average credit card	4,644
MemoryStick	3,010
SecureDigital	1,613
SmartMedia	1,265
MultiMediaCard	1,075

A PCMCIA card is an option when seeking to expand a PDA's functionality. PCMCIA cards, or PC cards for short, have long been industry-standard extensions for desktop systems. The physical hardware interface is not integrated into mobile devices as of yet because of the battery power required to supply the connector. To solve this problem, many devices feature sleds, an add-on that fastens to the PDA and allows PC card integration. PC cards are very taxing on batteries and are not seen as often in PDAs with smaller batteries. Sometimes PC cards exist as adapters for still other expansion cards, which are smaller. A PC card to Memory Stick adapter allows a Memory Stick to be inserted into a PC card. The Memory Stick can be inserted into a PC card in a laptop, for instance, and data can be transferred manually between the laptop and a PDA with a PC card adapter. Adapters are available for several additions, such as Secure Digital, SmartMedia, MultiMediaCard, and CompactFlash cards. For more information on PC cards, see http://www.pc-card.com. For more information on Memory Stick, see http://www.sony.com.hk/Electronics/pr_t/tec/memory.

One popular expansion module is Handspring's proprietary interface, Springboard. Boasting the largest physical capacity of the expansion cards, it also provides the highest data transfer rate. The data transfer rate is made possible by the attachment of I/O devices directly to the processor bus. Some Springboard modules support their own separate batteries to support functionality that requires more power. For more information on Springboard modules, see http://www.handspring.com/developers.

The CompactFlash card is supported across the board on most PDAs. It can be attached by insertion into a PC card adapter and provides additional memory to add-ons such as portable MP3 players or bar code scanners. CompactFlash cards also provide a platform on which additional functions can be built, such as serial ports, Ethernet cards, GPS devices, or modems. For more information on CompactFlash, see http://www.compactflash.org.

Secure Digital (SD) Memory Cards offer high storage capacity (32MB and 64MB currently and 128MB and 256MB scheduled for release), fast data transfer, and limited security. Their purpose is to store information downloaded from a desktop system and then transferred to a smaller device such as a PDA. For more information on SD Memory Cards, see http://www.sdcard.org.

Two other forms of expansion technologies are the MultiMediaCard, which acts as a storage medium for MP3 players, and SmartMedia (or Solid State Floppy Disk Card [SSFDC]), which acts as extra file storage space. Information about the MultiMediaCard can be found at http://www.mmca.org and about the SmartMedia card at http://www.ssfdc.or.jp/english.

Not all expansion interfaces are supported on all platforms. RIM's BlackBerry supports none of the expansions discussed here. High-end models of the EPOC platform support CompactFlash and MultiMediaCards. The Pocket PC offers limited integration with PC cards, CompactFlash, MultiMediaCards, and Secure Digital Memory Cards. Palm OS devices have some integration capabilities with all expansions mentioned except PC cards (although Springboard expansion modules can be used only on Handspring proprietary devices, which do use the Palm OS).