Data Acquisition

configuration of the programs stored on the PC Card. For plug and play to be fullyrealized, the PC, BIOS, PC Card, card and services software, and application softwaremust all follow the same PC Card standard. The problem is that PC Cards, PCs, andsoftware packages are made by different companies. Getting them to follow a voluntarystandard can be extremely difficult.Execute in place means that a PC Card such as a flash memory device can run a programfrom the card instead of downloading the program from memory. A floppy disk can dothis, but because of the seek-time on the drive, it takes too long. Flash memories havevery low seek-time and therefore it would be the same as having the program in thememory of the computer. Auto-execution of programs when the PC Card is inserted intothe computer has its own problems that are not within the scope of this book.The downside of the PC Cards is two fold. One is that the retailers have problems withthem being stolen because they are so small. If you wish to buy a PC Card, you usuallyhave to ask the retailer to open up a locked case where they are kept. The other problem isthat the external connectors are usually small. This means that they can easily break whenslightly tugged. It is best when PC Cards are used in a portable PC to mount the PC in adocking station or temporary jig so that the PC doesn’t move. Cables attached to the PCCard should be so placed that they are not snagged by accident.12.3 ProductsIn the beginning, the PC Card cards were just memory cards, but it soon became evidentthat this new format was perfect for all kinds of other devices. The manufacturers foundthat it was easy to include many functions on one card. The following is a short list ofdevices that are produced. Many of these devices can be combined on one PC Card.The memory cards include Flash memory, RAM, and ROM devices. Flash memory isused to download data, increase memory and load programs in products like data loggers.RAM cards are used as virtual floppy disk drives and ROM cards are used as fixedprogram cards.There are two types of disk drives for the PC Card. One is the all-electronic type. Thiscard uses RAM to save the information. The other uses a modified version of themechanical spinning magnetic disk. Both types of hard disk have their advantages anddisadvantages. The RAM based drive is faster and has no moving parts, but is veryexpensive at the moment. The mechanical drive is cheap and at the moment can holdlarger amounts of memory, but it is slow (12 ms seek-time) and prone to breakage due tothe presence of moving parts. Eventually the price of memory cards will fall and themechanical hard disk will go the way of the punch card.