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Network administrators can attest that one of the biggest problems with notebook computers is how to connect them to corporate networks. Distributed staff members need to be able to communicate with the network whether in an office building in New York, a hotel room in Los Angeles or an airplane over Chicago. The most recent PC Cards give users affordable solutions with virtually all of the functionality they require.

When Two Isn't Better Than One Administrators must decide whether a single combination PC Card is right for their users. Smaller, lighter notebook computers are sometimes forced to stack the two Type II slots (used by the majority of modems and network adapters).

This double-decker effect rarely lets both cards utilize pop-out connectors at the same time (however, few users need simultaneous dial-up and Ethernet connectivity). The larger problem comes from clogging both ports. Users also must be wary of stacked cards overheating due to a lack of ventilation.

Generally, the decision regarding separate adapters is based on convenience and personal needs. New technologies will always find their way into specialized adapters, and then be integrated into combination cards as the technologies become more mature. It is generally easier to carry one PC Card rather than two, but it could be just as tricky to juggle multiple network and modem connectors. Note that there are many more single-function PC Card mod ems and network adapters than there are combo cards.

Drivers present a significant issue; al though Microsoft Windows95 has eased PC Card installation and configuration through Plug-and-Play support, vendors generally include specific drivers for all of a card's features to work (there really aren't any default drivers for combo cards). Users can expect to see more native drivers in Windows97, to be released later this year.

The decision may have been made already for many notebook computer owners: The majority of high-end and ultralight portables include full-function fax/modems with speakerphones. IBM Corp.'s ThinkPad 760XD, for example, uses its Mwave DSP as a 28.8-Kbps fax/voice/modem.

The Maturity of Portable Ethernet Since the majority of notebook computers on the market today have only 16-bit PC Card slots, vendors continue to focus on 10-Mbps Ethernet adapters. These adapters include the most current Ethernet technologies being employed in ISA-based units, such as 3Com Corp.'s Parallel Taski ng technology. A caveat with the Parallel Tasking technology, however, is that it weeds out bad packets, and it does not fully allow for promiscuous, or packet-sniffing, mode.

The majority of cards have 10BASE-T (RJ-45) connectors, and 10BASE-2 (coaxial) functionality adds about $50 to a card's price. The adapters that include dual functionality have an autoswitching feature that detects which connection is in use. In previous testing, the adapters have performed well against their desktop counterparts. You should look for a top performer, but also focus on PC Cards that are power-conscious and compatible with your machines.

The 16-bit bus outlined in the PCMCIA 2.1 standard is sufficient for 10-Mbps Ethernet, but it cannot support 100-Mbps Fast Ethernet. CardBus, the new 32-bit, 33-MHz PC Card extension technology patterned after the desktop Peripheral Component Interconnect bus, provides PC Card performance similar to desktop PCI cards. Xircom Corp. and TDK Systems, two vendors with 100-Mbps CardBus o fferings, have 100-Mbps PC Card adapters that perform at roughly twice the speed of 10-Mbps Ethernet .