The GMCH Hub
The GMCH as the name suggests contains the graphics and memory controllers and the following its break down of components:
- System Bus Interface
- System Memory Interface
- Display Interface
- Display Cache Interface (82810-DC100 only)
- Digital TV-Out
- Clock Signals
- Miscellaneous Interface Signals
- Hub Interface
There are 2 versions of the GMCH, the 82810 GMCH and the 82810-DC100 GMCH. The main difference between them is that the DC100 version has the Display Cache Interface integrated which supports 4MB of external display cache. Both versions of the GMCH are pin-compatible, hence one manufacturer can have a low cost model and the premium model without the need to redesign the base model. Here's a schematic of the GMCH:-
While the Intel BX chipset is able to support up to 1GB of memory, the new i810 can only support 256MB of memory. This is the reason why you'll see up to 4 DIMM slots in the BX chipset based motherboard, which has 8 addressing lines to cater to 4 DIMM slots that can take in single or double-sided DIMMs mixed. The i810 has only 4 memory addressing lines, therefore motherboards based on the i810 chipset come with 2 DIMM slots that can take in either a pair of single or double-sided DIMMs mixed. Take note that double-sided DIMMs need 2 addressing lines each (and single-sided DIMMs need 1 addressing line) and these are usually available in either 128MB or 256MB DIMM modules. Since the i810 is for integrated cost-effective systems that won't run in servers that use ECC memory for safety, ECC support has been removed in the i810 chipset.
The Graphics Core
Graphics is handled by an integrated i752 core, which is basically a spruced up i740. Its key features include dual-rendering pipelines, motion-compensation for DVD, 1600 x 1200 pixels desktop resolution, 230MHz RAMDAC, 16-bit colour support in 3D and a Direct-AGP connection that is essentially a direct access to the system memory to store all graphics data as the GMCH itself has no local memory. What's more, the memory bus is locked at 100MHz, while the FSB can asynchronously run at 66/100MHz (officially, but there are the usual list of unofficial ones implement by the motherboard vendors). This means even if you intend to overclock the system by changing the FSB, the memory bus can still operate at 100MHz. This also means any standard PC-100 memory will do the job without you needing to hunt for those speedier and more expensive RAM. However you can't use your older PC-66 memory unless they happen to be of good quality and are happy to operate at 100MHz.
Now back to the Direct-AGP connection, since the graphics controller in the GMCH has a direct connection to the system memory, the bandwidth is 800MB/s (64-bit memory bus / 8-bits x 100MHz) and that is more than AGP 2X transfer rate of 533MB/s (32-bit / 8-bits x 133MHz)! Don't get excited yet because all the graphics adapters have their own local memory that has far higher bandwidth between the graphics chipset and the onboard memory, but once the graphics data (usually texture data) gets too large for the local memory, they'll have to spillover to the system memory if the graphics adapter uses an AGP connection. In that situation, the GMCH's integrated graphics becomes more favorable because of it's higher bandwidth to the system's memory. Even so, this won't be much beneficial as the graphics engine itself isn't as powerful as Intel's marketing marketing claims (would you believe NVIDIA Riva TNT-like performance from an i752 graphics core?)
Fortunately, the costlier version of the GMCH labeled as the i82810-DC100 can support an optional 4MB of local cache for the integrated graphics (the cheaper i82810 GMCH doesn't have support for the extra cache). The DC100 descriptor just means that it uses 100MHz cache. There is a possibility of a DC133 part because the BIOS of the test motherboard supports a cache speed setting of either 100 or 133MHz. The odd thing is that that there is a separate bus from the GMCH to the optional cache but it's only 32-bits wide, meaning it can only sustain a bandwidth of 400MB/s. Seems odd considering that the Direct-AGP to system memory connection sports a wider 800MB/s bandwidth but only half of that for the dedicated local cache. Fortunately the cache and its memory bandwidth is dedicated to the purpose of serving the integrated graphics engine and it helps reduce the system memory's burden. Overall the idea of dedicated cahce and the Direct-AGP connection is far better than the old UMA-architecture in older motherboard designs. Last but not least, take note that 1MB of your system memory is reserved for display frame buffer purposes from the second you power up your PC. Once in the Windows OS, it will use the Intel Dynamic Video Memory (D.V.M.) technology to freely allocate itself an appropriate amount of system memory as and when it needs to. Here's a snippet from Intel:-
The internal graphics device on both the 82810 and 82810-DC100 support Intel Dynamic Video Memory Technology (D.V.M.). With D.V.M, the allocated size of system memory used for display graphics can be dynamically altered. For example, if 2 MB of system memory is needed, the driver allocates this amount. If later, only 1.5 MB is needed, the driver allocates the 1.5-MB size freeing up the remaining 512 KB for system use.
In addition to D.V.M., the 82810-DC100 supports Display Cache (DC). The graphics engine of the 82810-DC100 uses DC for implementing rendering buffers (e.g., Z buffers). This rendering model requires 4 MB of display cache and allows graphics rendering (performed across the graphics display cache bus) and texture MIP map access (performed across the system memory bus) simultaneously. Using D.V.M. all graphics rendering is implemented in system memory. The system memory bus is arbitrated between texture MIP-map accesses and rendering functions.
This kind of integrated graphics solution can use some megabytes of your RAM when playing 3D games on top of the game's own memory requirements, so do make sure you take this into account when buying a game as well as spec'ing out your system memory. On a different note, we would like to reiterate that the integrated RAMDAC rated at a lowly 230MHz, but fortunately in our use, it managed a sharp output up to 1024 x 768 @ 75Hz. Over that limit, you'll get blurry output. If integrated graphics is something you cannot live with, there is a big drawback to expansion options on the Intel i810 chipset platform - it does not support an AGP connector! If this bothers you, you should invest in a conventional platform.