While at lower system load levels, the IHA is not necessary, at higher loads these optimizations can make the difference between skipping video and smooth video, and make a large impact on system bandwidth. Intel recently showed us a live comparison between a 440BX system and an i815E system, each using the same processor and amount of memory. Both machines were playing several MP3s, a DVD, and running a few other lesser tasks while running a load meter. The i815E system was running along without a skip and at about 50% CPU usage while the 440BX system was skipping consistently and had the CPU usage almost constantly pegged at 100%.
Of course, you have to keep in mind the fact that nobody in their right mind is going to make a habit of playing multiple MP3s at once while watching a DVD, but there are still real-world situations where such I/O could be needed. You could be watching time shifted TV from the hard drive in a window, where the computer is decoding and playing back an MPEG-2 stream, while you are soft-encoding the video stream of what is currently playing into MPEG-2 format onto the hard drive, and you are downloading files while listening to one MP3 and browsing the web. Scary as it may seem, this is a realistic computer usage situation that might require more I/O than the normal old 133MBps PCI bus could provide. By the way, if you find the usage situation we described appealing, you might need Ritalin.
And now we get to the meat. What are i815 and i815E? i815 is the matching of the Intel 82815 GMCH to the Intel 82801AA ICH, also known as just plain ICH. i815E is the matching of the Intel 82815 GMCH to the Intel 82801BA ICH, also known as ICH2. We will now go into the features of the 82815 GMCH followed by the features of ICH and ICH2.
The 82815 GMCH is a completely modern chip. It links to the CPU over a 133MHz FSB, can use up to 512MB of PC100 or PC133 memory, integrates Intel's own 2D/3D video core, and provides an AGP4x slot with fast writes support.
The 133MHz, 64-bit FSB provides 33% more I/O between the GMCH and CPU than the 440BX and i810's 100MHz FSB. This will help overall performance compared to these older chipsets, but AMD's 200MHz 64-bit FSB still provides significantly more bandwidth than the 82815 GMCH.