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.
Contents
[hide]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 |
The VGA controller inside the IGP is a "GeForce2 MX Integrated Graphics" (PCI ID:10de/01a0). Its internal name is NV1A.
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.
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).
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 been built, Intel made a better deal
- Microsoft agreed to have Intel CPUs; Intel had to modify AMD's chipset to support an Intel 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.