NForce

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This documents collects information about the Xbox chipset and its sibling, the nVidia nForce chipset, as well as further relatives.

nForce

The nForce chipset consists of the IGP (Integrated Graphics Processor) Northbridge and the MCP (Media and Communications Processor) Southbridge. Both are available in different flavours:

• IGP-64: 64 bit memory bus
• IGP-128: 128 bit memory bus (TwinBank), requires two DIMM modules for 128 bit operation
• MCP-D: includes Dolby Digital encoder
• MCP: Dolby Digital encoder disabled

So these are the four possible combinations:

	MCP	MCP-D
IGP-64	nForce 220	nForce 220D
IGP-128	nForce 420	nForce 420D

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The VGA controller inside the IGP is a "GeForce2 MX Integrated Graphics" (PCI ID:10de/01a0). Its internal name is NV1A.

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Although IGP-64 and IGP-128 are different and their respective chipsets have different codenames (Crush11 and Crush12, see below), there seems to be no difference from the software side:

• The VGA BIOS of the MS-6367 mainboard (nForce 420D configuration, i.e. Crush12) has the internal name "CR11BT.ROM". It also includes the strings "NVIDIA GeForce2 Integrated GPU", "CR11 Board" and "Chip Rev B2".
• The PCI IDs seem to be the same for the GPUs inside IGP-64 and IGP-128.

Crush

"Crush" was the codename of the nForce chipset. Crush11 is the nForce 220/220D/230/230-T, Crush12 is the nForce 420/420D/430/430-T, and Crush18 is the nForce2. The "11" probably derives from "NV11", the internal name of the GeForce2 MX.

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nForce & Xbox

The Xbox has an IGP-128 that uses an NV2A video core (PCI ID:10de/02a5), which is between the GeForce3 (NV20) and the GeForce4 (NV25). The Southbridge is called "MCP-X" and lacks the PCI card bus (PCI bus #1).

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AMD Heritage

There is the following rumour, which is not fully verified yet:

• Microsoft wanted AMD to make the CPU and the chipset for the Xbox, and nVidia to make the video hardware.
• When alpha hardware had already bee built, Intel made a better deal
• Microsoft agreed to have Intel CPUs; Intel had to modify AMD's chipset to support an AMD CPU
• Intel insisted that the brand name AMD could not be associated with the Xbox, so nVidia licensed the AMD chipset. Now the Xbox chipset was by nVidia.
• nVidia sold the same chipset for PCs, calling it "nForce".

This is the reason why

• the Xbox is the only nForce chipset with an Intel CPU
• the AMD chipset and the nForce chipset are so similar

Evidence:

• The AMD and nForce AMD IDE controllers are fully compatible. (Linux kernel: "AMD 755/756/766/8111 and nVidia nForce/2/2s/3/3s/CK804/MCP04 IDE driver for Linux." [12])
• The I2C/SMBus controller on the nForce is fully AMD-756/766/68 compatible. [13]
• The audio controller is i810 compatible - as is the audio controller of the AMD-768 and the AMD-8111.
• The nForce and AMD-768 modems are compatible.
• At least one register ("VGA_en") in the nForce PCI-to-AGP bridge is compatible with the AMD chipset (AMD-761, 24081.pdf, page 136).
• The nForce uses HyperTransport.
• [14], [15]
• "One man's guess, the silicon is not a major factor. Because the nForce and 760 MP have a similar pin count, they are going to be cost comparable." [16]

	Northbridge	Southbridge
AMD-760	AMD-761	AMD-766
AMD-760MP	AMD-762	AMD-766
AMD-760MPX	AMD-762	AMD-768

AMD-760™ Chipset Tech Docs AMD-760™ MP Chipset Tech Docs AMD-760™ MPX Chipset Tech Docs
The nForce chipset might be based on the AMD-760 chipset.

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