by Jeff 9 December 2002 Older and higher-priced Pocket PCs use NOR flash memory to store the OS. This is more expensive than NAND memory, and slower to write, but it does have one significant advantage. It has a wide data pipe that allows the device to run the OS and applications directly from flash, called "executing in place," or XIP. This is why a 64MB Pocket PC like the Toshiba e335 (which uses NOR memory) has nearly 64MB free after a hard reset. The OS itself is running, but it's running directly from flash.
NAND memory uses a serial pipe for data and can't support XIP. When a device using NAND memory starts up, it has to copy the OS and core apps into RAM and execute them from there. This is exactly the way PCs work, copying the OS from the hard drive to RAM before running it, and it's the reason you need both a hard drive and system RAM on a PC, rather than just one giant flash drive. NAND memory is significantly cheaper than NOR memory, though, and figures to be a popular choice in low-end Pocket PCs as a way to keep the price low and still make a profit on the device.
"Compact Flash" cards are 43mm x 36mm. "Type I" are 3.3mm thick, while "Type II" are 5.5mm thick. Each card contains a controller chip as well as the memory itself.