Choosing a Hardware Bus Type

When you install a card in a workstation or server, whether it is a network adapter card or a SCSI disk adapter card, you insert the card into a slot that connects the card to a bus . A bus is nothing more than a communications channel that devices can use to exchange information with the computer's CPU and memory. Different kinds of cards can be inserted into slots to connect them to the bus in the computer. Before you make a decision on what kind of network card to purchase, you need to know what kinds of bus slots are available on the computer. In addition, you may have more than one type of bus in your computer. For example, all major computer manufacturers today use the Peripheral Component Interconnect (PCI) bus (or a newer PCI standard, such as Mini-PCI in notebooks and small form-factor desktops). However, the universal serial bus (USB) is now pretty much a standard on desktop computers, and there are network adapters you can use with USB. The FireWire (IEEE 1394) bus is another competitor that offers a higher bandwidth than USB. PCI cards for both FireWire and USB can be purchased inexpensively if your computer does not come with them. As you read this chapter, keep in mind (1) the number of available slots you can use in an ISA/EISA bus or PCI bus, and (2) the number of devices you will use the USB or FireWire bus for. If your workstations are all newer models, you are most likely to find that only PCI slots are available. The need for older EISA slots has fallen dramatically since the PCI bus has become the norm for computers today.

Note

In addition to a computer's bus, you will find on the market today network adapters that do not need a bus at all. For example, there are USB-compatible network adapters. Just plug them in and configure the IP information, and you're on the network. Windows systems that support USB serial ports will automatically recognize and configure these types of devices.

Another network adapter that has just recently become an inexpensive solution for networking computers is the wireless network adapter, of which there are several types. The portability that wireless networking enables is one of its best features. There are some considerations, such as security, that are being addressed with newer standards. Because wireless networks are just now coming into the mainstream marketplace , wireless adapters are discussed in several chapters in Part V, "Wireless Networking Protocols."

In this discussion we'll start with the older technologies (some of which are still widely used) and then go on to discuss newer network adapter cards.

Note

Another matter to think about when installing a network adapter card is the underlying network. Most large networks use Ethernet for the wire protocol, and thus Ethernet cards are discussed in this chapter more than others. Yet, to accommodate home users, as well as small office/home office (SOHO) users, there are several other network technologies, such as wireless adapters and HomePNA (creating a network using your home's phone lines). Yet another thing to consider is that there are also two major serial port technologies that allow you to connect to peripheral devices, such as USB and FireWire. Both of these support network adapter cards as well as disk drives and other devices. This section covers the basic bus types used in computers that are in wide usage today, such as the desktop and laptop computers. Later in this chapter you will learn more about the different network cards, and how they fit into the picture.

ISA

The ISA (Industry Standard Architecture) bus was created in the 1980s and was the bus used by the first IBM personal computer architecture. Manufacturers adopted the term ISA as the IBM computer became a standard and vendors began to create many kinds of cards to expand the capabilities of the PC.

The first version of this bus provided for an 8-bit data channel. The IBM AT computer architecture used an enhanced version of the original ISA bus, allowing for data transfers at a rate of 8MHz, using a 16-bit data channel. This architecture was later expanded on, and the Extended ISA (EISA) bus was created. Although the EISA bus still operates at only 8MHz, it allows for a 32-bit path , allowing more data to be channeled through the bus. When you open a computer and look at the available slots, the EISA slots are usually the longer ones. The shorter ones are usually PCI (Peripheral Component Interconnect) slots. Figure 7.1 shows a picture of both EISA and PCI network adapter cards. The shorter footprint of the PCI card makes it easier to create PCs that have a much smaller design than in the past.

Figure 7.1. The network interface card on the left has an EISA interface, whereas the one on the right is designed for use in a PCI slot.

Note

As mentioned earlier in this chapter, most newer PCs ”particularly those built since 2000 ”are unlikely to include ISA slots on the motherboard.

Note

Another slot you might find in your computer is the Accelerated Graphics Port (AGP). You can usually distinguish this slot from other types of slots by its pin-out ”only an AGP card fits into the slot ”and its color , which is usually a beige or light reddish-brown. AGP slots generally are offset slightly from the PCI and ISA slots (if your motherboard includes them).

PCI

The PCI bus specifications have many advantages over previous standards, including dramatically faster data transfer rates and 32-or 64-bit-wide data paths. Devices on the PCI bus can also use a feature called bus mastering , whereby a card can take control of the bus and directly transfer large amounts of data to system memory without using the CPU. Some PCs today contain a mix of both PCI and EISA slots. However, most PC vendors are ending support for older ISA and EISA products, a trend that will increase over the next few years . It is more often the case now that you will find only PCI slots in newer computers. The ISA/EISA buses have become legacy hardware.

Besides its performance advantage over the EISA bus, the PCI bus also allows for auto-configuration . A PCI card contains internal registers that hold information used for configuration when the system is booted . The kind of information that is stored in these registers includes a 3-byte class code, which indicates the card's base class. For network cards, the value found in this register is 02h. Other possible classes include mass storage controllers (value = 01h), display controllers (value = 03h), the memory controller (value = 05h), and so on. There's even a class represented by the value 00h, which is used for cards that were created before the definitions of class codes were finished, and a class using the value FFh, which indicates that the device doesn't belong to any of the defined classes.

Other information contained in the PCI card's registers tells the system-specific configuration information about the PCI card, such as IRQ (Interrupt Request, or in older documentation, Interrupt Request Line) and memory information.

Note

An IRQ is a hardware component of the computer that devices can use to send an interrupt signal to the CPU in an attempt to get the attention of the processor. For example, when a network adapter needs to transfer data from its buffer into the computer's memory, it will use the IRQ assigned to it to notify the CPU that a request is pending. Using the IRQ line does not guarantee that the device will get an immediate response from the CPU, however. The CPU might be executing instructions that cannot be interrupted . This kind of interrupt, also referred to as a maskable interrupt , is the most used type of interrupt. Another type of interrupt is called a non-maskable interrupt , which is used to signal the CPU that a more serious condition exists and needs to be addressed. For example, a memory error or a critical hardware error is likely to generate a non-maskable interrupt. Although the CPU can ignore a non-maskable interrupt by setting a flag, this is rarely the case.

Usually the PCI card is configured to use an available IRQ when the system detects it. If an unused IRQ isn't found, the card can, under some circumstances, share an IRQ with another card. In that case, the system interrogates each card that shares the IRQ when the CPU receives the interrupt request. The card making the request can then communicate with the CPU to satisfy the request. Sharing IRQs should usually be done among similar devices.

Note

In addition to the bus types discussed in this chapter, you might occasionally hear about the MCA bus. MCA stands for Micro Channel Architecture. This bus was a proprietary standard that IBM created in 1987. Although MCA was, in most respects, superior to the other bus specifications at that time , it is not compatible with other buses. Because incorporating MCA technology required licensing it from IBM, card manufacturers never widely adopted MCA. Instead, the EISA specification was developed partly in response to the proprietary nature of MCA. And now the EISA bus has become obsolete.

PCMCIA

Although PCI slots are used in most desktop and server computers for holding adapter cards, smaller computers, such as laptops, are another matter altogether. Because of their size, it's not possible to include a similar setup of expansion slots that conform to conventional PCI specifications. PCI cards just won't fit into the smaller form factor provided by laptop computers.

PCMCIA cards are credit-card “size cards that can be used in laptops and other small computers. The acronym does not stand for "People Can't Memorize Computer Industry Acronyms," which is a popular phrase used to remember the acronym. Instead, PCMCIA is the Personal Computer Memory Card International Association, which is a nonprofit organization responsible for promoting standards for making cards for smaller computers, such as laptops. Although the first cards that were produced according to specifications by this organization were memory cards, you can now find all sorts of add-in cards for laptop computers, including network adapter cards. The term PCMCIA has been used in the past to describe these cards, but current products now use the name PC Card . Several varieties of cards currently are on the market, but most use a standard 68-pin connector. If you have to connect a laptop to the local LAN, you'll need to evaluate this card to find one that works with your operating system. In Figure 7.2, you can see an example of an Intel PC Card network adapter.

Figure 7.2. PC Cards are much smaller than standard network adapter cards.

The PCI bus also has several variants, such as the Mini PCI, CompactPCI, Low-Profile PCI, Concurrent PCI, and PCI-X specifications, each of which is used to create a PCI-compliant bus in different computer configurations. For example, the Mini PCI bus is generally used in laptop or smaller computing devices. This PCI bus is implemented as a card that you can install in one of these smaller computer devices to enable connections to other peripheral devices, such as modems and (the topic of this chapter) network adapter cards.

Note

You can use the URL www.pcmcia.org to find more information about PCMCIA cards. This trade organization has been around for many years and has been responsible for many developments in this small form factor card for use in laptop computers and, more recently, consumer devices such as digital cameras and set-top boxes for cable television. In addition, this organization also defined the standards for the PC-Card specifications, which have supplanted the older PCMCIA cards for the most part.

In addition, the PCMCIA organization has another Web site that provides a large directory of PC Card devices, as well as resources for developing PC Cards. Use the URL www.pc-card.com to access this site.

CardBus

In 1996, the PCMCIA organization developed the CardBus for use in small computing devices, such as laptop computers. This standard provides a 32-bit data path, which can enable PC Card devices to operate four to six times faster than earlier 16-bit cards. In addition, CardBus devices consume less power than older cards. In most cases a computer that uses CardBus is backward-compatible with older PC Card devices.

So, which kind of card should you choose for your networking needs? That can depend on many factors. For example, you might be limited on the kind of card by how many slots are available in the computers, and of what type. If you have a workstation that already has filled all its PCI slots, you might be forced to use an EISA card if you can't sacrifice one of the existing PCI cards to free a slot. However, if your hardware supports them, the obvious choice is to purchase newer PCI-based cards.

Note

If you want to get a greater understanding of how the types of buses discussed in this chapter work, I recommend that you check out Upgrading and Repairing PCs , by Scott Mueller, which also is published by Que. Visit www.upgradingandrepairingpcs.com to learn more about this industry classic.

InfiniBand Still Has Many Opportunities

Recently many of the larger hardware vendors, such as Intel, have stopped developing low-level chips for InfiniBand. This doesn't mean that InifiniBand is not going to be a major standard in the future. Indeed, InfiniBand is the next logical solution for a very complicated problem: the increasing need to relieve a CPU from I/O devices. Today the economics for large corporations make it a more practical venture to let smaller chip vendors develop silicon for this type of architecture, which can later be incorporated into InfiniBand products by the higher-level manufacturers who can license the technologies from smaller companies.

Note

Another new technology that will be in the marketplace soon just might take over the role of network adapter cards on large servers. The technology? InfiniBand. InfiniBand was developed to solve many problems associated with I/O between the computer's CPU/memory and external devices. By using fiber optics and a switched network, InfiniBand greatly extends the connectivity between the CPU, memory, and other components of a high-end system. You can learn more about InfiniBand at the Web site for the InfiniBand Trade Association: www.infinibandta.org. InfiniBand essentially removes the SCSI interface from a server and substitutes a switched network of devices, much like those used in a Storage Area Network (see Chapter 11, "Network Attached Storage and Storage Area Networks").

Different Cards, Different Speeds

Another factor to consider when making a network card purchase is the speed of your network. Standard 10BASE-T networks operate at 10Mbps. If you are upgrading, it is more likely that you'll be using or upgrading to at least a 100Mbps network. If so, you'll probably be upgrading the backbone cabling that connects your switches/routers also to a higher bandwidth, such as Gigabit Ethernet.

If you are creating a new network, simply choose 100Mbps cards. If you are upgrading an existing network, and if the cabling infrastructure supports 100Mbps, you can slowly migrate users to 100Mbps by purchasing cards that operate at both speeds. Most 10/100Mbps cards also support autosensing , which means that they can detect the speed of the network connection and adjust accordingly . When you swap out hubs or switches to upgrade to a faster network, you won't have to worry about reconfiguring or buying new adapter cards for end- user workstations. Therefore, if you are currently operating in a 10Mbps environment but know that you will have to upgrade to 100Mbps in the next year or two, spend the extra few dollars to buy cards that operate at both speeds. And those old machines still using 10Mbps should be destined for the recycling bin shortly anyway.

Besides making purchasing choices for network adapter cards, plan ahead for other equipment you might need to buy, such as a new hub (or more likely a switch) to accommodate the speed of the network adapters that are used on your network. If necessary , get one that supports both speeds and autosensing (to detect the speed of the card/switch), and preferably one that works in dual 10/100 mode. For more information about hubs and switches, and these features, see the chapter "Bridges, Repeaters, and Hubs," on the upgradingandrepairingpcs.com Web site. Also check out Chapter 8, "Network Switches."

Network Cable Connectors and Terminators

In Chapter 6, "Wiring the Network ”Cables, Connectors, Concentrators, and Other Network Components," the various kinds of network cables and connectors that can be used to create a LAN were examined. Although most older 10BASE-2 networks have already been upgraded to 10BASE-T (or faster) networks, there are still a few around that use thinnet coaxial cable with BNC connectors and terminators. If you are operating a LAN of this kind, be sure that any new network card purchases are "combo cards," as shown in Figure 7.3. These cards let you either connect a BNC T-connector to the card or use an RJ-45 jack for the newer 10BASE-T networks. In all probability, you will have a difficult time finding network cards that support only BNC connectors anymore. Purchasing combo cards means that you can still use the adapter when you upgrade to 10BASE-T. However, I suspect that this will be a rare situation. If you are still operating with coaxial cables in your Ethernet network, you need to immediately turn to the upgrading section of this book and start your planning there.

Figure 7.3. A combo card contains both a BNC and an RJ-45 receptacle and can be used on both types of networks.