iMac Developer Note

This note describes the iMac with SuperDrive computers, introduced in September 2006, based on the Intel Core 2 Duo microprocessor. It includes information about distinguishing features of the computers, 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 iMac comes with Mac OS X version 10.4.7 installed.

The value of the 17-inch and 20-inch iMac model identifier string is iMac5,1.

The value of the 24-inch iMac model identifier string is iMac6,1.

Architecture

The architecture of the iMac is based on the Intel Core 2 Duo microprocessor, the North Bridge memory controller, and the South Bridge I/O controller. The North Bridge and South Bridge are 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 internal graphics controller. The South Bridge IC supports these components:

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

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, and an integrated IR receiver to work with 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 2 Duo Microprocessor

The microprocessor in the iMac is an Intel Core 2 Duo with the following features:

  • 17-inch iMac: 2.0 or configure-to-order 2.16 GHz dual-core processor

  • 20-inch iMac: 2.16 or configure-to-order 2.33 GHz dual-core processor

  • 24-inch iMac: 2.16 or configure-to-order 2.33 GHz dual-core processor

  • 4 MB shared L2 cache

  • Intel Advanced Digital Media Boost

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

  • Supports Intel Extended Memory 64 Technology (EM64T)

See the Intel Core 2 Duo Processors support site for detailed microprocessor documentation.

Intel Advanced 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. Advanced Digital Media Boost supports Intel Streaming SIMD Extensions (SSE) versions 1, 2, and 3 and allows the processor to execute an SSE3 instruction every clock cycle.

For information on Advanced Digital Media Boost, refer to Technology@Intel Magazine.

When the iMac is executing a 64-bit application, EM64T provides the following features:

  • Virtual 64-bit addressing significantly increases the amount of physical memory that can be addressed, enabling larger sets to be stored in memory for faster processor operation.

  • Extended 64-bit registers allow single operations with integers larger than 32-bits and enable 64-bit addressing.

  • Eight new general purpose registers improve performance on recompiled applications.

  • Eight new SIMD registers improve multimedia performance on recompiled applications.

For information on EM64T, refer to the following website:

http://www.intel.com/technology/64bitextensions/

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 iMac 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. The iMac ships with two 512 MB DDR2 SDRAM SO-DIMMs for a total of 1 GB memory. Maximum memory capacity is 3 GB. 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 data 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 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, supported graphics cards, and display capabilities, refer to Video 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, the South Bridge controller provides an Ultra ATA/100 interface to the slim slot drive, SuperDrive that operates at UATA/33. The drive can read and write CD media and read DVD 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

6x (CAV max)

8x, 4x, 2x, 1x (ZCLV) single-layer, depending on media

DVD+R DL

6x (CAV max)

2.4x (ZCLV) double-layer, depending on media

DVD-ROM

8x DVD5 (CAV max); 6x DVD9 (CAV max)

–

DVD-RW

8x (CAV max)

4x, 2x, 1x (ZCLV) depending on media

DVD+RW

6x (CAV max)

4x, 2.4x (ZCLV) depending on media

CD-R

24x (CAV max)

24x PCAV (ZCLV)

CD-RW

24x (CAV max)

16x ZCLV (high speed media)

CD-ROM

24x (CAV max)

–

The optical drive is configured as cable select and complies with the ATA/ATAPI-5 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 17-inch and 20-inch iMacs support two IEEE-1394a FireWire 400 ports at transfer rates of 100, 200, and 400 Mbps. The 24-inch iMac supports one IEEE-1394a FireWire 400 port at transfer rates of 100, 200, and 400 Mbps and one IEEE-1394b FireWire 800 port at transfer rates of 100, 200, 400, and 800 Mbps. For more information, see FireWire Developer Note.

Ethernet Controller

The iMac has a built in Ethernet port for 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 IR receiver, Bluetooth + EDR, 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

The iMac has an internal AirPort Extreme module connected to a dedicated 1-lane PCI Express link with antennas built into the enclosure. For more information, see AirPort Developer Note.

Bluetooth 2.0 + EDR Module

The iMac comes standard with an internal Bluetooth 2.0 + EDR (enhanced data rate) module, with an antenna built into the enclosure. The Bluetooth module is connected via the internal USB 2.0 controller. For more information, see Bluetooth Developer Note.

Audio System

The iMac has a built-in microphone, a combined analog audio in and S/PDIF digital optical audio in jack, and a combined analog output and S/PDIF digital optical audio out jack. 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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