Specifications

This chapter describes the Power Mac G5 computer’s built-in I/O devices and the ports for connecting external

I/O devices. Each of the following sections describes an I/O port or device.

USB Ports

The Power Mac G5 computer has two external Universal Serial Bus (USB) 2.0 ports on the back and one on the

front of the enclosure and an internal connection to the AGP slot for the Apple display. The external USB ports

are off of the USB controller connected to the PCI bus, bridged by K2. In addition, there are two USB 1.1 ports

on the keyboard. The USB ports are used for connecting the keyboard and mouse as well as additional I/O

devices such as printers, scanners, and storage devices.

All USB ports are fully compliant with the USB 2.0 specification, including support for high-speed (480 Mbps)

devices using an Enhanced Host Controller Interface (EHCI). Ports are automatically routed to a companion

OHCI controller when a classic-speed (full-speed or low-speed) USB device is attached to a root hub port.

Each USB rear port is connected to a separate USB root hub in classic speeds, allowing the USB ports to support

12 Mbps devices at the same time with no degradation of their performance. The USB root hubs are also

connected to the internal USB modem.

The three external USB ports comply with the Universal Serial Bus Specification 2.0. The two ports on the

keyboard comply with the Universal Serial Bus Specification 1.1 Final Draft Revision. For low-speed and full-speed

devices, the USB register set complies with the Open Host Controller Interface (OHCI) specification. For

high-speed devices, the USB register set complies with the Enhanced Host Controller Interface (EHCI)

specification.

For more information about USB on Macintosh computers, please refer to Apple Computer’s Accessing Hardware

from Applications and the other sources listed in USB Interface (page 67).

Input and Output Devices