Input and Output

In addition to communicating with other computers, the Macintosh must communicate with the devices you use to operate it. That's the function of its many input/output (I/O) subsystems, which connect such basic peripherals as the keyboard and mouse as well as such exotics as digital musical instruments and video cameras.

DVI

Digital Visual Interface (DVI) is an industry-standard protocol for the digital interface between digital displays and computers. Apple implements DVI support on the Power Mac G4 (PCI Graphics) and Power Mac G4 (AGP Graphics), the PowerBook G4 (DVI), PowerBook G4 (12-inch) and later models, PowerBook G4 (15-inch FW800) and later models, PowerBook G4 (17-inch) and later models, the Mac mini, and the Power Mac G5 and later models. The Apple DVI Macintosh computers use the DVI-I connector, which supports both digital and analog signals, as opposed to the digital-only DVI-D connector.

DVI to ADC Adapter

The Apple DVI to ADC (Apple Display Connector) Adapter, shown in the following illustration, connects Apple digital flat-panel displays to the DVI port of the PowerBook G4 and to some Power Mac G4 configurations, including models with the NVIDIA GeForce4 Titanium graphics controller.

Apple's ADC interface carries DVI signals as well as additional USB signals and power to drive Apple's older series of stand-alone flat-panel Cinema displays, such as the Apple Studio Display 17-inch ADC. This meant that a single ADC cable is all that is needed to connect between the Macintosh and display, reducing cable clutter. These older ADC displays require the DVI to ADC adapter in order to connect to DVI-equipped Macintosh desktops and portables. Newer standalone Apple flat panel Cinema displays do not require this adapter, because these newer displays use a DVI interface and can therefore connect directly with any DVI-equipped Mac or PC.

The DVI to ADC Adapter can boost the DVI signal to produce maximum image quality on large, high-resolution flat panels. The adapter includes an integrated power supply, an AC power cord, and an approximately six-foot cable that transmits USB and DVI data. Stand-alone Apple flat-panel displays that used the ADC interface attach directly to the ADC port on the adapter.

FireWire

Apple uses the term FireWire and the FireWire logo, which are licensed and copyrighted by Apple, to refer to the IEEE 1394 technology, of which Apple was the principle developer. Now, many other computer platforms use the technology. Apple implements FireWire on the Power Macintosh G3 (Blue and White), all Power Mac G4 and G5 models, all slot-loading iMac models except the original, the iMac (Flat Panel), the eMac, Mac mini, Xserve, all iBook models since the first FireWire-equipped model, the PowerBook (FireWire), and all PowerBook G4 models.

iLink is Sony's registered trademark for its IEEE 1394 devices. Sony's iLink-compatible cameras may not mention FireWire or 1394, but they are fully 1394-compatible.

FireWire 400 and FireWire 800

FireWire 800 (IEEE 1394b) has several important improvements over the original FireWire 400 specification:

• Its maximum speed has doubled from 400 Mbit/s to 800 Mbit/s.

• The range has increased greatly. FireWire 800 extends signaling distance up to approximately 328 feet, compared to FireWire 400's 15 feet.

• FireWire 800 cabling uses a 9-pin connector instead of the 4- and 6-pin connectors of FireWire 400. Here you see the FireWire 800 port with the 9-pin connector.

FireWire Extensions

Mac OS X loads a number of FireWire extensions into memory at startup. They are located in /System/Library/Extensions. You can watch Mac OS X detect FireWire ports and connected FireWire devices during startup by turning on verbose mode (hold down Command-V while the computer starts up). You can also use System Profiler to view information about your FireWire port and any connected devices.

FireWire Ports

Many Apple computers have two external FireWire IEEE 1394 ports. Their capabilities include:

• Support for serial I/O at 100, 200, 400, and 800 Mbit/s

• Providing up to 6 watts of power when the computer is on and not in sleep mode

• Accepting external power input from the bus

• Starting up the system from a mass storage device

• Target Disk Mode support

The FireWire hardware and software provided with the computers are capable of all asynchronous and isochronous transfers defined by IEEE standard 1394.

FireWire Connectors

There are two different FireWire 400 connectors. The larger of the two was created in the 1394 specification and has six contacts, while the smaller, which has only four contacts, was developed primarily for digital camcorders, because they have so little room for connectors. The smaller connector has only four contacts because it carries only data, not power. Most digital camcorders don't draw power over FireWire. Most other FireWire devices, such as hard disk drives, use the 6-pin connector and typically don't require an external power supply, because they draw power from the computer, although some do require an external power supply.

Adapters and special 4- to 6-pin cables enable the use of 4-pin FireWire devices on 6-pin connectors.

FireWire Booting

UMA-based Macintosh computers can boot from any FireWire storage device that implements Serial Bus Protocol 2 (SBP-2) with the RBC (reduced block commands) command set.

Mass Storage Devices

When connected to another computer by a FireWire bus, UMA-based Macintosh computers can operate in Target Disk Mode as a mass storage device.

MIDI

Using Musical Instrument Digital Interface (MIDI), music-related devices can communicate with each other and with Macintosh desktops and portables over a serial interface, either directly via USB, or via MIDI cables and connectors, which require a separate USB to MIDI adapter. MIDI communication doesn't carry the music itself; instead, it carries instructions, such as what instrument or sound to play and when to play it.

MIDI assigns each musical device a unique numeric address, so applications can send instructions to each device independently. For instance, an application that orchestrates music can send the instructions for the drum part to a drum machine, the brass and woodwind parts to a keyboard, and the string parts to a sampler.

Most studios use a collection of MIDI devices to produce music, but connecting many MIDI devices together can be complicated. Mac OS X includes software to integrate MIDI devices, including an Audio MIDI Setup utility. Audio MIDI Setup is located in the /Applications/Utilities folder.

Mac OS X includes frameworks or resources to support MIDI in the /System/Library/Frameworks directory.

Audio MIDI Setup can discover MIDI devices that are attached to the computer and display them in its window, where you can then establish links (and hierarchical links) between devices.

PCI

Peripheral Component Interconnect (PCI) slots are available in the Power Macintosh G3 (Blue and White), all Power Mac G4 models except the Cube, and all Power Mac G5 computers (all the other recent Macintosh computers have PCI buses internally, even though they don't have PCI slots for expansion cards). Typically, a desktop system has three or four 33 MHz slots that can take 32- or 64-bit cards. You can install a 66 MHz card in a 33 MHz slot, but the card will run at only 33 MHz, and its operation may become unstable. The maximum power consumption of all PCI cards on the bus should not exceed 50 watts.

Some Power Mac G5 models support PCI-X cards instead of PCI cards. PCI-X is a newer specification that addresses the need for increased bandwidth of PCI cards. PCI-X works with systems and devices that operate at clock speeds up to 133 MHz, or 1 gigabyte per second (GB/s).

SCSI

All Macintosh computers starting with the Macintosh Plus had an external Small Computer System Interface (SCSI) port used primarily for external hard disk drives, and the SCSI controller chip also managed the internal hard disk drive. Over time, Apple migrated to the more common integrated drive electronics/advanced technology attachment (IDE/ATA) bus for its internal drives and dropped the external SCSI port altogether. Because many other vendors have embraced the IDE standard, IDE drives are often more economical than SCSI drives, but the latest SCSI standards provide greater performance. To that end, for customers who demand maximum drive speed, any PCI-based Macintosh can have a SCSI card installed.