Working with External Interfaces

The most obvious data input and output interfaces are those whose ports are located on the outside of the machine. Modern Macs have a number of built-in interfaces you can use to move data into or take data out of the machine.


All data that travels around your Mac eventually moves from one device to another. When data "crosses over," it is said to have crossed a bus. A data bus is simply a channel through which data flows. There are many buses inside your Mac, and all devices have at least one bus (the point at which data enters or leaves the device).



If you want to really dive into the details of computer buses and other technology, check out Although this site is PC-focused, it does contain lots of great general information that is equally applicable to the Mac. For example, you can learn all you need to know about the various hard drive technologies at this site in addition to finding detailed information on memory buses, monitors, and just about anything else about which you want to learn.


Ethernet is the interface that is used for almost all Local Area Networks (LANs). Ethernet is designed for hub-based networks, which means that information flowing across the network is controlled to some extent by a central Ethernet hub.

All modern Macs have built-in Ethernet ports to enable you to network with other machines; Ethernet on all modern Macs uses an RJ-45 connector, which looks like an overgrown telephone connector (see Figure 20.1).

Figure 20.1. All modern Macs have an Ethernet port. The only variation is in the speed that the port supports.


Three different speeds of Ethernet are supported by the Mac. These are the following:

  • 10 megabits per second (Mbps) This was the speed of the "original" Ethernet.

  • 100BASE-T This flavor of Ethernet is 10 times as fast as the original and is also known as Fast Ethernet. It communicates at speeds up to 100Mbps. All modern Macs support at least 100BASE-T Ethernet.

  • Gigabit Ethernet The newest Ethernet standard can communicate at 1,000Mbps. Newer Power Mac G4 machines support Gigabit Ethernet.


The Power Mac G4 was the first PC to support Gigabit Ethernet as a standard feature. It follows in the tradition of earlier Macs, which were the first to provide built-in Ethernet support as standard equipment.

Ethernet-capable devices can communicate at various levels of speed up to their maximum speed (such as Gigabit Ethernet). Higher-speed devices can communicate at lower speeds, but lower-speed devices can't communicate at the higher speeds. Therefore, data speed over Ethernet connections always defaults to the maximum speed of the lower-speed device.

A protocol is the "language" in which data is being communicated over a particular interface at a particular time. The physical interface might be able to transmit data in more than one protocol. For example, Ethernet can be used to transmit data in the AppleTalk protocol as well as using TCP/IP (Transmission Control Protocol/Internet Protocol).

All Ethernet devices are designed to work with an Ethernet hub (or router) that acts as a traffic controller for the data being communicated among the attached devices.

Ethernet is used exclusively for networking computers to hubs or routers or to other computers.

To learn more about Ethernet hubs, see "Finding and Installing an Ethernet Hub," p. 710.

To learn more about creating and using an Ethernet network, see Chapter 25, "Building and Using a Network," p. 721.

Direct Connect Ethernet

Because Ethernet is designed to be used with hubs, you can't simply connect two Ethernet ports together to connect two machines. Instead, you have to use a special Ethernet cable, called a crossover cable. Using such a cable, you can connect any two Ethernet devices directly. If you use a standard Ethernet cable, the devices must be connected with an Ethernet hub.

An exception to this is the Ethernet port on newer PowerMac G4s and G4 PowerBooks. It can sense if it is connected to another device or to a hub and configure itself appropriately for either situation using a standard Ethernet cable.


FireWire is a fast technology that provides an interface for many types of peripheral devices. FireWire was designed to enable very high data rate transfers, such as those required to move digital video data. FireWire is relatively new to the Mac, but has quickly been applied to all modern Mac models.


FireWire is Apple's brand name for an industry-standard interface definition. The actual specification for the interface is IEEE 1394. Other companies use specific names for their implementation of the interface, such as Sony's term for it: iLink.

FireWire offers several major advantages, which are the following:

  • High speed FireWire is capable of communicating at up to 400Mbps, making it suitable for many high-bandwidth applications.

  • Chainable FireWire devices can be chained together; the interface supports up to 63 devices per port.

  • Hot-swappable FireWire devices can be connected to your Mac while the Mac is running.

  • Self-powered The FireWire interface is capable of providing power to a peripheral device through the bus. Devices that use the capability don't require a separate power supply.

FireWire connectors are an unusual shape and consist of a rectangle with a triangular top section (see Figure 20.2). FireWire ports are marked with a high-tech?looking "Y."

Figure 20.2. FireWire ports can be used for various devices, the most prominent of which are digital video cameras.


The connector shown in Figure 20.2 is that used to connect FireWire devices to your Mac. Consumer and other FireWire-equipped devices can use differently configured FireWire ports. For example, you won't find a port like that shown in Figure 20.2 on a DV camera. Because of size limitations, DV cameras use a much smaller FireWire port that looks quite different from the FireWire ports on a Mac. Typically, these devices include the specialized cable that you need to attach their ports to the FireWire port on your Mac.


FireWire connectors are relatively delicate. You should always exercise care when connecting a FireWire device to a FireWire port. The pins in the connector are somewhat fragile and can be bent if you attempt to insert the connector when it is not aligned properly.

Because of its ability to move large amounts of data quickly, the FireWire interface is used for several devices, including the following:

  • Digital video cameras

  • External hard drives

  • External CD drives, including CD-RW and DVD-R drives

  • Scanners


Apple's implementation of FireWire has led the industry. For example, Apple is almost single-handedly responsible for the dramatic rise in the use of digital video technology. Most other computers still require that a separate card be added in order to be able to use devices that transfer data via the FireWire interface.

FireWire's "competitor" is the USB 2 interface. USB 2 is much faster than the previous USB specifications, but still isn't as fast as FireWire. Why hasn't everyone adopted FireWire then? Mostly for business and PR reasons. Apple is a leader in the FireWire arena, and Intel probably doesn't want to be cooperative with anything Apple is leading. So the platform wars continue. FireWire has been adopted by some key companies, such as Sony, but it remains to be seen whether FireWire will become a dominant interface on Windows PCs or whether USB 2 will be the norm.


Peripheral Component Interconnect (PCI) is actually an internal interface that is used to provide additional external interfaces for specific purposes through PCI cards. These cards are plugged into available PCI slots inside the Mac, and then the ports provided by that card become available for you to use (see Figure 20.3).

Figure 20.3. This photo shows the three open PCI slots in a Power Mac G4; a graphics card occupies the AGP slot located toward the bottom of the photo.



AGP is the abbreviation for Accelerated Graphics Port. On Macs that include PCI slots, the AGP slot is filled with the graphics card that is installed in the Mac when it is built.

Adding PCI cards to a Mac is rather straightforward. You open the Mac's case, remove a blank cover from an available slot, insert the card into an available slot, and replace the screw that holds it in place. After any required software is installed, the ports provided by that card become available.

One of the best applications of a PCI card is to add a second monitor to your Mac by adding a second graphics card to it. On the newer Power Mac G4s, the video card already supports dual monitors, but on those machines, you can add more graphics cards to add even more monitors.

To learn more about installing a second monitor for your Mac, see "Installing and Using a Second Monitor," p. 664.

Many PCI cards are available for your Mac, including the following:

  • Graphics cards

  • Video digitizers

  • Other interfaces (such as SCSI)

  • Advanced audio cards

Earlier Power Mac G4 models came with four PCI slots; one was occupied by the graphics card installed by Apple leaving three open slots as shown in Figure 20.3. Beginning with the models released in January 2001, Power Mac G4s have four open PCI slots plus the AGP slot occupied by a graphics card.


PCI is also an industry-standard interface. Earlier in the Mac's history, Apple used a proprietary interface, called NuBus, to accomplish the same purpose. Because NuBus cards were unique to the Mac, there were fewer types available and those that were available were also expensive. Wisely, Apple adopted the PCI standard, which means that Macs can use the same PCI cards as PCs can. Developers need only provide Mac-specific software to enable their devices to work with the Mac.


A modem (MOdulator-DEModulator) is another interface device that provides networking services to your Mac. The great benefit of a modem is that it can provide these services over standard phone lines, thus enabling the age of online services?most importantly, the Internet.

Specific modem hardware implements a specific communication standard, with more modern standards providing higher-speed connections. The current dial-up modem standard is V.92. Modems supporting this standard are capable of communicating at 56,700 bps (bits per second, more commonly referred to as 56K). Although dial-up modem speed has increased significantly over the past few years, it is still relatively slow, especially for data-intensive applications, such as video.

All modern Macs include a built-in modem capable of 56K speeds.


As with Ethernet, the actual speed obtained with a dial-up modem depends on each side of the connection. The communication speed between two devices is the highest speed at which they both can communicate. Because dial-up modems use phone lines, they are also greatly affected by the noise that is prevalent in most telephone architectures. Unless the phone lines used are exceptionally "clean," it is unlikely that modem communication will occur at the maximum speed possible.

There are other types of modems as well, including cable, DSL, and so on. These modems provide much greater speed and reliability, but depend on the respective service being available to you.

For more on modems, see "Choosing a Modem," p. 718.


The Universal Serial Bus (USB) is an interface that also provides access to external peripheral devices for your Mac. USB is a fairly slow interface, and is capable of transferring data at the rate of 12Mbps. Although slower than many of the other interfaces, this speed is more than adequate for many peripheral devices.

USB ports on Macs have a thin rectangular shape (see Figure 20.4).

Figure 20.4. USB ports enable you to connect your Mac to a large variety of devices.



Similar to FireWire, the USB ports on peripheral devices can look quite different from the USB ports on a Mac. Many USB devices have a USB port that is almost square; others have specialized shapes (such as those on digital still cameras that tend to be quite small).

USB offers advantages that are similar to those offered by FireWire:

  • Chainable As with FireWire, USB devices can be chained together. A single USB port can support up to 127 devices.

  • Hot-swappable USB devices can be connected to or unconnected from your Mac while it is running.

  • Self-powered The USB interface can also provide power to a peripheral device, so that such devices do not require a separate power supply.

Apple Leads Again

Adoption of the USB interface across the entire computer industry can also be largely attributed to Apple. Although USB is an industry-standard interface, it was not widely used until Apple released the iMac. The success of the iMac encouraged other computer manufacturers to more strongly support the adoption of USB. All PCs are now also equipped with USB ports. Eventually, USB will replace several different ports on the PC (such as the parallel port) as it has on the Mac.

Because USB is an industry-standard interface, Macs can use the same USB hardware as PCs do. The manufacturer only has to provide Mac-specific software for the device to be Mac compatible.

All modern Macs are equipped with at least one USB port and most have two or more. To connect more USB devices, you can install a USB hub for your system.

To learn more about USB hubs, see "Finding, Installing, and Using a USB Hub," p. 714.

Numerous devices can use the USB interface, including the following:

  • Mice

  • Keyboards

  • USB hubs

  • Printers

  • Digital cameras

  • Microphones

  • Speakers

  • CD-R and CD-RW drives

  • Cradles for Palm OS devices

  • Scanners


Although USB supports up to 127 devices and FireWire supports up to 63, these are somewhat theoretical limits. The actual number of devices you can connect to these ports depends on the power requirements of the devices. For example, you could not connect 127 USB devices that get their power from the USB interface to a single Mac because the bus could not provide enough power for all those devices.

USB 2 is a much faster implementation of the USB interface. In fact, USB 2 is so much faster that it is suitable for hard drives and other high data rate transfer devices (FireWire is still faster and is capable of much more). USB 2 is becoming a standard on Windows PCs. USB 2 and USB 1 devices can exist on the same USB chain. To take advantage of USB 2, a computer must have a USB 2 controller. Because Intel is a prime driver behind USB 2, it is reasonable to expect that USB 2 will be standard on Windows PCs.

Mostly for business reasons (Apple is part of the consortium that developed and supports FireWire), USB 2 is being pushed in the PC world instead of FireWire for higher speed devices. It remains to be seen what kind of USB 2 support Macs will provide by default, if any. To use USB 2 devices in current Macs, the appropriate controller hardware and software must be installed.


The video interface in the Mac provides the video output of the machine to a monitor or other device. Depending on the particular Mac model you are dealing with, several different types of video interfaces might be available. On Power Mac G4s, you can add more video options through PCI cards.

Power Mac G4 Cubes and Power Mac G4s have at least one built-in graphics card (in the Power Mac G4, this card occupies the AGP 4x slot) to which you attach a monitor or other display device. Although PowerBooks, eMacs, iMacs, and iBooks have built-in monitors, the PowerBook, eMac, iMac, and newer iBook also have external video interfaces so that you can connect them to external displays, projectors, and other display devices. (You can also attach a USB video device to enable Macs to provide output to external displays.)

Apple Display Connector (ADC)

The Power Mac G4 and short-lived Power Mac G4 Cube include the Apple Display Connector (ADC) (see Figure 20.5). This video connector is proprietary to Apple and was designed primarily for its Cinema Displays and is now supported on all Apple external displays. The ADC carries several different data streams, those being analog video, digital video, USB, and power. This enables ADC-equipped machines to take advantage of all the features of digital flat-panel monitors.

Figure 20.5. The ADC interface provides video, USB, and power so that you can take advantage of the advanced features of Apple's Cinema Displays.


For information about working with ADC devices, see "Finding, Installing, and Using a Monitor," p. 660.


In Figure 20.5, you can also see that the three PCI slots are still available (the "blanks" are still installed). If other PCI cards were installed, you would see the additional ports that those cards would provide.

Mini D-Sub VGA Connector

All Macs provide a standard Video Graphics Array (VGA) port to which you can attach a monitor or other display device (see Figure 20.5). The benefit of the VGA port is that VGA is the video standard for the PC as well, so you can use just about any monitor with a Mac that has a VGA port.


Some Macs, such as iMacs and eMacs, provide only a "duplicate" image through the VGA port to that of the desktop. For example, when you connect an external monitor or projector to an iMac, the image you see on that device is the same as that on the iMac's monitor. This is called video mirroring.


The Digital Video Interface (DVI) is designed for flat panel digital displays. The DVI interface is standard on all digital flat panel displays, except Apples that use the ADC interface. Modern Power Mac G4s include video cards that offer both ADC and DVI ports so that you can use either type of display. You can also connect a display to each port so that you have two monitors available. (To use dual Apple displays, you must connect one of them through a DVI/ADC adapter.)


Interestingly, support for VGA or analog monitors for Power Mac G4s requires an adapter. The age of analog monitors on Macs is mostly over (the exception is eMacs that include a flat CRT monitor).

S-video Connector

Some Macs, such as the G4 PowerBook, include an s-video output port. S-video provides a high-quality video signal and can be connected to television monitors, VCRs, and other video devices.


The list of video interfaces in this section is by no means exhaustive. For example, many PCI video digitizing cards provide other video ports, such as those for standard RCA video inputs and outputs.


Several basic audio interfaces are provided on specific Mac models. Some models, such as the iBook, have only one audio interface (the headphone jack). However, there are many audio devices that use the USB or FireWire interfaces (such as microphones, speakers, and so on), so even the lack of audio ports does not really limit you too much.

Standard audio ports on Mac models include the following:

  • Headphone jacks to which you connect standard headphone mini-jack connectors.

  • Speaker jacks to which you can attach speakers. The difference between a headphone jack and a speaker jack is that headphone jacks provide amplified signals, but speaker jacks generally do not (most computer speakers are externally powered).

  • Microphone jacks to which you can attach a microphone. Strictly speaking, you are supposed to use PlainTalk-style microphones in the microphone jacks in Macs. These microphones have longer plugs that make contact in different places than a standard mic jack. However, for some uses and with some Macs, a standard microphone will work just fine. You can also obtain adapters or use a USB microphone.


Some Mac models, such as iMacs and PowerBooks, have built-in microphones.

For information on speakers, see "Finding, Installing, and Using Speakers," p. 669.

As with video, many PCI cards provide additional audio interfaces.

PC Card

PowerBooks support the PC card interface. This interface provides a slot into which you can plug PC cards to add additional capability to the PowerBook.

Technologies Supported by OS X, but Not Part of Modern Macs

When Apple moved to USB and FireWire as the primary external interfaces, it left behind some of its previously standard interfaces. Some older Macs, such as beige G3 Power Macs, might have these interfaces, and they are supported by Mac OS X.

  • Apple Desktop Bus (ADB) The ADB port was used to connect mice, keyboards, and other input devices to the Mac. ADB devices were sometimes difficult to work with because they were not hot-swappable; removing an ADB device from or attaching such a device to a running Mac could cause major problems (in some cases, doing so wrecked the machine's motherboard).

  • Serial bus Previous-generation Macs used two serial ports: the Modem port and the Printer port. These ports were actually functionally identical and provided an interface to printers, modems, digital cameras, and other devices.

  • SCSI The Small Computer System Interface (SCSI, which is pronounced skuzzy) is a general interface for attaching various devices to a computer. Older-generation Macs included an external SCSI port to which you could attach a chain of SCSI devices. The SCSI interface is a relatively fast one, but it is also relatively difficult to work with. Each device has to have a unique identifier, and each SCSI bus was limited to seven devices. Creating SCSI device conflicts is easy to do, and the cables and connectors are large and can be hard to work with.


You can add an external SCSI interface to Power Mac G4s by adding a SCSI PCI card. This enables you to connect and use external SCSI devices, such as hard drives, scanners, and so on. Of course, you will need the appropriate Mac OS X drivers to be able to use such devices.

For more on SCSI, see "SCSI," p. 637.


A great resource on the Net from which you can learn about various interface technologies is In addition to plenty of information about input and output technologies, you can find information on just about any computer-related terminology you encounter. When you find a term, you are also presented with links to additional sites at which you can get more detailed information.

    Part I: Mac OS X: Exploring the Core
    Part III: Mac OS X: Living the Digital Lifestyle