Unlike desktop PCs, portable systems don’t have standard expansion slots for the peripheral device connections. The expansion slots in a desktop computer allow additional devices to be attached to the computer. However, due to size and weight constraints, these slots are not available in the portable computers. Instead, they have expansion slots called PC Card slots or Personal Computer Memory Card International Association (PCMCIA) slots. PC Cards that can be inserted in these slots resemble a credit card in appearance and size, though they’re slightly thicker. Originally, these slots were intended for memory expansion. But now, such devices as hard disks, CD-ROM, LAN cards, and modems can also be connected using these slots.

A PC Card may have a data cable to the external power supply. For example, the card for a CD-ROM drive must be connected to a wall outlet for power supply. If the card doesn’t contain the data cable, the care is self-contained, like a modem card that draws power from the battery instead of an AC outlet. Depending on the size and number of connectors on the card, there are three standards for the PC Card slots:

Type I. Up to 3.3 mm thick, with a single row of sockets. These usually add Static RAM (SRAM) to the portable system.

Type II. Up to 5.5mm thick, with two rows of sockets and a pop-out RJ-45 or RJ-11 connector. These add modems and NICs to the portable system.

Type III. Up to 10.5 mm thick, with three rows of sockets. These connect hard disk drives and adapters for CD-ROM, DVD, and tape drives. Often, each type of slot is included in a portable PC. For better performance, look for a PCMCIA specification called CardBus slot. It’s the latest slot type, and it increases I/O speed and supports 32-bit buses and low voltage. To support PC Cards, the operating system in the portable computer must provide two services:

1. Socket service. A BIOS-level service detects when a PC Card is inserted into or removed from the system and manages the sockets.

2. Card service. This service provides the interface between the card and the device driver when the socket is closed. It manages the assignment and allocation of the system resources, such as I/O addresses and IRQs, to the PC Card.

Adding a PC card

One of the most popular features of a PC Card is hot swapping. This allows you to install a device while a computer is still running. The computer recognizes the device without rebooting. With this feature, you can remove a card and insert another without switching off the machine.

The steps for adding or installing a PC Card are:

1. Insert the card in the slot. Make sure that the notched edge of the card goes in first. Don’t use extra pressure or force while inserting the card. You may damage the card and the slot.

2. Press the card into the connector so that it’s firmly in place. If the card is installed correctly, the Eject button (either inside the PCMCIA opening or on the side of computer next to the slot) pops out.

3. If a device driver comes with the card, install the driver.

Removing a PC Card

To remove a PC Card, press the Eject button. The card pops out. If it doesn’t, either refer to the user manual or contact the support personnel. Do not use the end of a paper and stick it in the slot. Portable computers are not as sturdy as desktop computers.

Make sure that any slots that aren’t used are closed or sealed. The slot connectors are very small. Small amounts of dust can cause big trouble.