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All the I/O interfaces and the video display system are on the main logic board. The controller ICs on the main logic board are connected to the PCI bus, which also communicates with the processor module.
The I/O controller IC in the Macintosh iMac computer is an ASIC called Paddington. The Paddington IC is an integrated I/O controller and DMA engine for use in Power Macintosh computers with a PCI bus.
The Paddington IC contains the PCI bus arbiter. It also provides the interface and control signals for
The Paddington IC is similar to the Heathrow IC used in the Power Macintosh G3 computers and Macintosh PowerBook G3 computers. The main difference is that the Paddington IC supports 100Base-TX Ethernet as well as 10Base-T.
The USB controller is a standard IC with two USB connectors. The register set complies with the Open Host Controller Interface (OHCI) specification.
The display subsystem consists of a graphics controller ASIC, 2 MB of SGRAM on the main logic board, and a connector for an additional 2 MB or 4 MB of SGRAM on an SO-DIMM. For information about the SGRAM SO-DIMM, see Chapter 4, "Expansion."
The graphics controller IC is an ATI Rage IIc. It contains 2D and 3D acceleration engines, a digital video port, front-end and back-end scalers, a CRT controller, and a PCI bus interface with bus master capability.
For information about the display and supported resolutions, see Chapter 3, "Devices and Ports."
The built-in hardware modem is a separate module that is connected to the SCC port A of the Paddington IC. The module contains a modem controller IC, a datapump, and the interface to the telephone line (DAA).
The infrared link module is a separate printed circuit board that is connected to SCC port B of the Paddington IC.