iMac Developer Note

This note describes the iMac computers based on the Intel Core Duo microprocessor and introduced in January 2006. It includes information about distinguishing features of the computer, including components on the main logic board: the microprocessor, the other main ICs, and the buses that connect them to each other and to the I/O interfaces.

The computer comes with Mac OS X version 10.4.5 installed.

The value of the iMac model identifier string is iMac4,1.

Architecture

The architecture of the iMac is based on the Intel Core Duo microprocessor and two custom ICs, the North Bridge memory controller and the South Bridge I/O controller, connected to each other by a Direct Media Interface (DMI) bus. The North Bridge IC provides the bridging functionality among the processor, the memory system, the DMI, and the 16-lane PCI Express bus to the graphics controller. The South Bridge IC supports these components:

A DMA controller internal to the South Bridge supports LPC DMA (low pin count direct memory access). The DMA controller has registers that are fixed in the lower 64 KB of I/O space. The DMA controller is configured using registers in the PCI configuration space.

Figure 1 provides a simplified block diagram of the North Bridge and South Bridge ICs and the buses that connect them together.

Figure 1  Block diagram
This block diagram shows the memory controller and I/O controller ICs and the buses that connect them on the main logic board. Each component in the block diagram is defined in text.

Features

The iMac computer includes a programmable Apple Mighty Mouse, a built-in iSight video camera, an integrated IR receiver, and the Apple Remote. For a complete list of user-visible features, see the iMac specification sheet at Apple's Specifications site. Other features are described in this section.

Intel Core Duo Microprocessor

The microprocessor in the iMac is an Intel Core Duo with a clock speed of 1.83 GHz in the 17-inch configuration and 2.0 GHz in the 20-inch configuration. It has the following features:

  • 1.83 GHz or 2.0 GHz dual core processors

  • 2 MB shared L2 cache

  • Digital Media Boost

  • Connection to the North Bridge IC over a 667 MHz frontside bus

See the Intel Core Duo Processors support site for detailed microprocessor documentation.

Digital Media Boost

Intel Digital Media Boost accelerates data manipulation by applying a single instruction to multiple data at the same time, known as SIMD processing. SIMD technology accelerates vector math operations and floating-point calculations. Digital Media Boost supports Intel Streaming SIMD Extensions (SSE) versions 1, 2, and 3.

For information on Digital Media Boost, refer to the following websites.

http://www.intel.com/products/processor/coreduo/digitalmediaboost.htm

Processor Bus

The processor bus is an up-to-667 MHz bus connecting the processor to the North Bridge IC. The bus has 32-bit wide data running in both directions. The processor has 32-bit addressing.

The point-to-point architecture provides each subsystem with dedicated bandwidth to main memory. The North Bridge IC implements an independent processor interface. The input clock to the processor PLL is 166 MHz.

Memory

The computer provides two RAM slots that accommodate 200-pin DDR2 SDRAM SO-DIMMs up to 1.25” in height. The SO-DIMMs must be DDR2 PC2-5300-compliant and must be unbuffered, unregistered, 8-byte, nonparity, and non-ECC. For additional information, refer to RAM Expansion Developer Note.

Direct Media Interface Bus

The North Bridge and South Bridge ICs are connected by a Direct Media Interface (DMI) bus, a high-speed, bidirectional, point-to-point link supporting a clock rate of 1 GBps in each direction

Extensible Firmware Interface (EFI) Boot ROM

The Extensible Firmware Interface (EFI) boot ROM consists of 2 MB of on-board flash EEPROM. It includes the hardware-specific code and tables needed to start up the computer, load an operating system, and provide common hardware access services.The EFI boot ROM connects to the South Bridge via the Serial Programmable Interface (SPI) bus.

Graphics/Video Subsystem

The graphics subsystem includes an ATI Radeon X1600 IC, with 128 MB GDDR3 SDRAM, connected to the North Bridge IC by a x16 link (16 lane), dual simplex, 2.5 GHz PCI Express bus. The iMac has a mini-DVI connector for an external video monitor and supports video mirroring mode and extended desktop display mode. For more information on the graphics subsystem and display capabilities, refer to Video Developer Note.

For more information on PCI Express, refer to PCI Developer Note.

Serial ATA Drive Interface

The iMac supports a 7200 rpm Serial ATA (SATA) disk drive through an AHCI 1.1 controller that supports advanced SATA-II features Native Command Queuing (NCQ) and PHY power management and operates at Serial ATA Gen-I (1.5 Gbps) interface speed. NCQ increases performance on random workloads by allowing the drive to re-order commands to reduce seek time and increase transactional efficiency.

For more information on SATA, see the Serial ATA International Organization (SATA-IO) website.

For information on the AHCI controller, see http://www.intel.com/technology/serialata/ahci.htm.

Ultra ATA Interface

In the iMac computer, the South Bridge controller provides an Ultra ATA/100 interface to the slot-loading, 8x SuperDrive with double layer burning capability. The drive can read and write DVD media and CD media, as shown in Table 1.

Table 1  Types of media read and written by the SuperDrive

Media type

Reading speed

Writing speed

DVD +/- R

8x (CAV)

8x ZCLV

DVD+R DL

8x (CAV)

2.4x CLV

DVD-ROM

8x (CAV)

–

DVD-ROM DL

8x (CAV)

–

DVD +/- RW

8x (CAV)

4x ZCLV

CD-R

24x (CAV)

24x ZCLV

CD-RW

24x (CAV)

8x ZCLV

CD-ROM

24x (CAV)

–

The SuperDrive is cable-select as device 0 (master) and complies with the ATA/ATAPI-7 industry standard. For information on parallel ATA interfaces, see the International Committee on Information Technology Standards (INCITS) Technical Committee T13 AT Attachment website.

FireWire Controller

The computer has two IEEE-1394a FireWire 400 ports, which support transfer rates of 100, 200, and 400 Mbps. For more information, see FireWire Developer Note.

Ethernet Controller

The computer has a built in Ethernet port for a 10BASE-T/UTP, 100BASE-TX and 1000BASE-T Gigabit operation. For more information, see Ethernet Developer Note.

USB 2.0 Controller

The South Bridge IC includes an integrated USB 2.0 controller supporting three external USB ports, the Bluetooth module, the IR receiver, and the built-in iSight camera. The USB ports comply with the Universal Serial Bus Specification 2.0. For more information, see Universal Serial Bus Developer Note.

AirPort Extreme and Bluetooth 2.0 + EDR Module

The iMac computer has an internal AirPort Extreme module connected to a dedicated 1-lane PCI Express link and a Bluetooth 2.0 + EDR (enhanced data rate) module connected to the USB 2.0 controller. AirPort Extreme and Bluetooth have built-in antennas. For more information, see AirPort Developer Note and Bluetooth Developer Note.

Audio System

The computer has a built-in microphone (located at the top of the display), and both an analog audio line-in jack and a combined analog and S/PDIF digital optical audio line-out jack on the rear panel. For more information, see Audio Developer Note.

System Management Controller

The iMac uses an advanced system management controller (SMC) to manage thermal and power conditions, while keeping the acoustic noise to a minimum. The SMC is fully independent of the operating system.



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