9 Apr 1995

Installing the LAN Card

A few PC models come with Ethernet built-in on the system board. Most PC's require an adapter card. The adapter receives commands and data through the PC I/O bus. Outbound data is stored in memory on the card until there is an opportunity to transmit it through the LAN. Arriving messages are stored on the card until the PC software can copy them to main memory.

Major chip vendors have reduced the important Ethernet logic to a single chip. A large number of companies can then produce inexpensive Ethernet boards. Currently, adapter prices range from $55 to $120. The higher priced cards may be more thoroughly tested and have more memory to hold messages. However, the main difference is software support.

Novell was an early player in Ethernet. Several years ago, however, it dropped out of the hardware business to concentrate on selling software. It allowed other companies to make clones of its popular designs, commonly known as the NE1000 or NE2000 adapters. One big advantage is that Novell continued to provide the necessary software to run the cards.

Many third party Ethernet Adapter cards run adequately on plain old Windows 3.1 and perhaps even on Windows for Workgroups. However, one should not assume that they will work on Windows 95, OS/2 Warp, or Windows NT until they have been tested (or are at least listed by name in the Hardware Compatibility List for the operating system).

At Yale, the network staff becomes responsible for the support of anything we sell. There is no way to be sure what users will want to run on their systems. Nextstep? Linux? Workplace OS? There is a big enough problem supporting Windows for Workgroups 3.11 on major brand Ethernet cards without worrying about clones and future operating systems. The opportunity to save $20 to $40 dollars a card is simply not worth the headache.

Yale typically uses 3Com Ethernet cards. This is the most widely known and supported brand. Three cards deserve particular mention:

DEC was an early player in Ethernet, but not in PC's. DEC is one of the few vendors that continues to ship cards that do not emulate one of the standards (NE2000 or 3C509) and require their own Drivers. This would not be a problem if DEC had any decent track record writing drivers. However, DEC doesn't seem to be able to coordinate hardware and software development. This may be caused by the continued attempt to push ancient versions of Microsoft networking under the name "Pathworks". These cards are best avoided unless you plan to run just plain Windows.IBM may have the technically best card. There have been recent reports of serious bugs in common Ethernet chip sets under conditions of unusually heavy load. The IBM adapters were the best performers and were the most reliable. IBM adapters emulate the ancient standard NE2000 hardware interface and are therefore generally supported in most operating systems. IBM had a slanted view against Windows NT, but the requirement to support NT 3.5 on the Power PC using the IBM ISA Ethernet adapter card seems to have changed this. An IBM Ethernet adapter is required for any server machine that intends to support remote dial-in users through IBM's LAN Distance software package.


Each adapter card is accompanied by a book from the vendor describing its configuration. Some options will be changed by moving "jumpers" (small metal plugs that connect two pins on the adapter board). Some options are controlled by switches. More recent adapters are distributed with a configuration utility diskette that can set hardware options from a menu. Options can also be set from parameters in the network software configuration files after DOS loads.

The PC architecture defines four major hardware parameters for any adapter

Ethernet adds one additional consideration:

Address - It is an almost universal convention that the first LAN adapter in a PC gets address 300. Frequently this must be expressed in "C" language notation as "0x300". This is the factory default, and though it can be changed, it is almost improper for any other type of card to be using this address. Unfortunately, the Creative Labs Sound Blaster 16 has a switch that selects between 300 and 330, so if you use this type of sound card and 330 is already in use, then you have to give 300 up to the Sound Blaster and choose another address for the LAN.

Memory- Early Ethernet adapters provided data buffers that became part of the PC memory. This behavior was an option on the 3C503. It is possible to do a complex analysis of the relative speed of moving data between the adapter and computer memory using ordinary I/O calls or the shared memory option. It is probably more important that shared memory makes configuration very difficult and uses DOS Upper Memory Blocks (UMBs) that can otherwise hold device driver and other system routines. Where possible, this option should be disabled. Unfortunately, it is not possible to disable shared memory on IBM Ethernet adapters.

Interrupt - The Ethernet adapter must be assigned a unique interrupt level number. With the 3C509 this is done using the hardware configuration utility diskette. With the 3C503, the interrupt level number is configured into the software later on. The safest choice is typically to select an interrupt number reserved by the architecture for a device that you do not have and do not intend to buy. Options include:

    5 - Reserved for a second parallel printer  port 

Connector - A card can connect to the Ethernet using a 15 pin plug (the AUI or DIX connection), a "Thinnet" connector (BNC), or Telephone Twisted Pair (10BASET). In current use, 10BASET is the most common choice. The physical connection at the wall jack will determine which choice to make. All vendors make Ethernet cards for all types of connectors, and some cards support all three types of connection on the same card. Often, however, there is a big ugly connector that has to be moved up or down on a block of pins depending on the type of connection in use.

There is a diagnostic program supplied on the floppy disk that comes with the card. If it runs successfully, then the address is correct and most of the hardware on the card has been checked out. Three common types of failure occur:

  1. You get a message indicating network failure as DOS is starting. This problem is usually caused when the Memory on the card was not disabled and the EMM386 memory optimizer supplied with DOS or windows tries to use the enabled memory location for other purposes.
  2. The system comes up, but no server or station on the network can be found. This usually means that the wrong connector has been selected, and the card is looking for data on the DIX plug while the network is actually connected to the 10BASET plug.
  3. The network occasionally hangs. This can be caused by two devices using the same interrupt level. For example, setting the Ethernet adapter to use interrupt 7 (not recommended above) would cause the network to fail when something starts printing.

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Copyright 1995 PC Lube and Tune -- Windows on the World -- H. Gilbert