Front & Backside of "Intel iMac" Motherboard: Non-Intel Chips Used for I/O-associated LSIs

Jan 19, 2006
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The Intel iMac mother board is considerably large, measuring 180 mm vertical x 330 mm horizontal (each at the longest section). It appears that the chips are not crammed together, but rather are implemented with a comparatively large amount of room. An Intel memory controller LSI, an I/O LSI, and modules for IEEE802.11 compliant wireless LAN and Bluetooth are found on the front side of the board.

Mounted on the backside of the board are a microprocessor, a graphics LSI manufactured by ATI Technologies Inc., and Ethernet, IEEE1394 and USB2.0 connectors. These connectors are attached aslant with respect to the board to allow for the curved surface on the rear side of the iMac chassis.

As mentioned above, the Intel iMac deploys non-Intel LSIs except for the microprocessor and chipset. Although the memory controller LSI "945GM" mounted in the Intel iMac includes a graphics drawing circuit, this circuit is not used in the iMac. Instead, an ATI's graphics LSI is provided separately. The LSIs for Gbit Ethernet, IEEE1394 and wireless LAN are also non-Intel. "We did not follow the entire reference design specified by Intel Corp.," said a spokesperson for Apple Computer, Inc., whose statement seems to be proven right.

The wireless LAN module marked with the model number "BCM94311MCAG" is surmised to be OEMed for Apple from Broadcom Corp. According to the information posted on Broadcom's website, the LSI "BCM4311" used in this module supports 802.11a which utilizes the 5-GHz band in addition to the 2.4-GHz band used by 802.11b/g . Although the module is equipped with two terminals for antenna connections, only one of them is used in the iMac. Considering that the product code ends with "AG," the wireless LAN module itself may support IEEE802.11a as well.


Takeyoshi Yamada, Nikkei Electronics

The motherboard detached from the Intel iMac (front side). The upper left is a heat sink for the microprocessor mounted on the backside of the board. The Intel memory controller LSI (north bridge) "82945GM (945GM)" is provided beneath another heat sink located in the center of the board.
The motherboard detached from the Intel iMac (front side). The upper left is a heat sink for the microprocessor mounted on the backside of the board. The Intel memory controller LSI (north bridge) "82945GM (945GM)" is provided beneath another heat sink located in the center of the board.
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The heat generated in the microprocessor mounted on the backside of the board flows through a heat pipe into the heat sink. The heat sink is fixed to both the front and backside of the board such that the heat pipe and sink sandwich the board.
The heat generated in the microprocessor mounted on the backside of the board flows through a heat pipe into the heat sink. The heat sink is fixed to both the front and backside of the board such that the heat pipe and sink sandwich the board.
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The mainboard without heat sinks, etc. (front side). On the left of the center is the Intel memory controller LSI (north bridge) "82945GM (945GM)." The I/O controller LSI (south bridge) "82801GBM (ICH7-M)" is located on the right of the center. The Bluetooth and IEEE802.11 wireless LAN modules are provided at the right and lower left of the board, respectively.
The mainboard without heat sinks, etc. (front side). On the left of the center is the Intel memory controller LSI (north bridge) "82945GM (945GM)." The I/O controller LSI (south bridge) "82801GBM (ICH7-M)" is located on the right of the center. The Bluetooth and IEEE802.11 wireless LAN modules are provided at the right and lower left of the board, respectively.
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The backside of the mainboard. Intel Core Duo processor is disposed askew at the upper right of the board. The ATI's graphics LSI "Radeon X1600" is located in the center. The black part at the lower right of the center is a connector to a power supply circuit. (Click to view the enlarged image.)
The backside of the mainboard. Intel Core Duo processor is disposed askew at the upper right of the board. The ATI's graphics LSI "Radeon X1600" is located in the center. The black part at the lower right of the center is a connector to a power supply circuit. (Click to view the enlarged image.)
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