You might be familiar with PC operating systems such as WIndows, Mac OS, and Linux. PDA's have several operating systems, too. The most common are the Palm OS (from Palm), and PocketPC (from Microsoft, the old Windows CE). 

The operating system is a set of programs that communicates between the physical machine and the application software. You might imagine it as a layer: the middle of a sandwich where the machine is the bottom piece of bread and the application program is the top piece.

Picture Element. One dot on a screen. Computers write to video memory in basically the same way, whether the screen is monochrome or color. Generally, if you have 65,000 colors, it means that you have 16-bit pixels, because 2 raised to the 16^th power is 65556 or so. In that kind of a color scheme, there are 4 bits each for red, blue, and green, often displayed in "hexadecimal" or base 16, which goes from 0 to F. Black is FFF, white is 000. Since a 16-bit pixel takes 4 times as much information to render as a 4-bit pixel, some PCs encounter a bottleneck at the video adapter. You "pay" for that extra data to be transported every time you draw a screen. If you don't need lots of colors, and your computer runs slowly, think about using less colors. Or buying a bigger Video card!

Liquid Crystal Display. First developed by RCA in 1968.

Thin Film Transistor. Sandwiched between glass and clear layers, there is a transistor for each pixel of the display. This is also referred to as "Active Matrix" display, because the display can be updated faster than a passive matrix. For example, as a mouse is dragged across a passive matrix LCD display, it disappears momentarily. The current required to update an active matrix display is much less, and the response appears to be instantaneous.

Highly Reflective Thin Film Transistor

Original Palm PDAs had a 160x160 pixel display. Current products feature 240x320 and they look more like the form factor of a pc screen, and have sharper pictures. The Clie N760C has a 320x320 display. This is like having 4 original palm screens to work with, dot-wise.

Displays were originally monochrome. There are still 16 gray (4-bit) monochrome devices for sale. The color devices are 16-bit pixels, offering 65,000 colors. VGA is back!

Springboard slots are unique to Visor PDAs, such as the Handspring. They were the original PDA expansion slots, and started the wave that became CF and SD.

CompactFlash™ (CF™) cards are small, removable mass storage devices. CF cards are an industry standard format that can be Type I or II. Type II is 5mm thick, Type 1 is 3.3mm thick. Type I cards work in all slots, Type II requires a Type II compatible slot, due to its width. CF cards are the size of a matchbook and weigh approximately one-half ounce. Available CF cards range from 8MB of RAM to the 1GB IBM MicroDrive. The Microdrive needs a Type II slot. The Microdrive is pictured below. Warning - these devices draw battery power, and some run hot.

CompactFlash cards are designed with flash technology, a non-volatile storage solution that does not require a battery to retain data indefinitely. CF storage products are solid state, meaning they contain no moving parts, and offer much greater data protection than conventional magnetic disk drives.

The expansion card slot will also accept I/O devices based on the industry standard CF format such as wireless modems, modems, Ethernet, serial, digital phone cards, laser scanners, Bluetooth wireless, etc.

For more information about the CompactFlash standard, contact the CompactFlash Association.

Secure Digital (SD) memory cards are next generation memory devices that offer an incredible combination of high storage capacity, currently 16, 32, and 64MB, and data security. SD cards are the size of a postage stamp, 32mm X 24mm, and a mere 2.1mm thick. One SD slot can generally be used for either Secure Digital or MMC cards.

SD cards are non-volatile, solid-state, and require no battery power to operate. SD cards feature unique, proprietary security functions that have been incorporated into the card’s controller, facilitating the secure distribution of content to devices. In addition, the card features a physical protection tab on its outer edge, providing users with an easy way to ensure their data is write-protected. The expansion card slot will also accept I/O devices, including those that use the new Bluetooth protocol.

For more information about the Secure Digital standard contact the SD Card Association. Secure Digital expansion is an open standard being developed by the SD association. Members include Sandisk, Olympus, Toshiba, Qualcomm, Hewlett Packard, and Phillips Electronics.

MultiMediaCard (MMC) is an industry standard high storage capacity device the size of postage stamp, weighing less than two grams. Maximum size of available MMC devices is 64MB. 

Like CF cards, MMC cards are non-volatile, solid-state and require no battery power to operate.

For more information about the MultiMediaCard standard, contact the MultiMediaCard Association.

ROM stands for Read Only Memory. The information in this memory is generally "burned" into the chip one time, at the factory. Often in the PDA world, it holds the operating system - Palm OS, Windows CE, Pocket PC 2002 and so on. ROM memory is fast to start up and fast to load, and more "durable" (less prone to corruption) than RAM.

RAM stands for Random Access Memory. This generally refers to memory that is like a tablet and an eraser - you can write anything you want on it and re-use it many times. Generally, RAM is "volatile," meaning that when the electricity is turned off, the memory is erased. Some electronics devices have "non-volatile" RAM and recover their contents when turned off and back on.

The original PCs had 256K bytes of memory. Now many of them have a gigabyte available. The original Palm Pilots had 2MB of RAM. The models available today have either 8MB or 32MB, but some are upgradable to 128MB.

Flashable ROM is ROM that can be "re-burned" or "flashed." This is a form of investment protection - the operating system can be updated without having to buy a new PDA, or having to remove and replace the ROM chips.

A word of caution - A flashable ROM means that you can completely change the application layer, flash a new ROM for the OS, and use the same machine. That can be useful sometimes, but PDA manufacturers really don't know what kind of upgrades to the OS will be needed in four years. There is no special reason to believe that the hardware can easily be pressed into radically different uses than those it has at manufacture. Still, Palm has upgraded the Palm OS a number of times, and it can represent a method for delaying obsolescence.