The Chipset

Glancing through the specs, you can’t see anything exceptional about the RADEON 9100 IGP. More to that, while the North Bridge is quite up-to-date, the South Bridge is closer to the chipsets of tomorrow. Here is the flowchart of the RADEON 9100 IGP:

Formally, the North Bridge supports Pentium 4 processors family with 400/533/800MHz FSB, contains an integrated graphics core, but is also capable of working with external AGP 8x graphics cards. The chip supports Hyper-Threading and features a dual-channel 128-bit memory controller supporting DDR400/333/266 SDRAM. It seems like these qualities make it a good alternative to Intel’s integrated chipset, i865G.

This is only a superficial impression, though. I should note that the support of the 800MHz Quad Pumped Bus and DDR400 SDRAM are dubious qualities of the RADEON 9100 IGP. At least, ATI didn’t dare to name them officially on the announcement of the chipset, but revised the specs later. Moreover, first mainboards on the RADEON 9100 IGP to appear didn’t support processors with the 800MHz FSB at all.

This problem was partially solved later. Off-the-shelf mainboards on the ATI RADEON 9100 IGP that have become now available do support the 800MHz QPB and DDR400. My experience with such mainboards tells me that this support is not universal and comprehensive. The new chipset from ATI sets strictest requirements to the memory modules working at 400MHz. Some DDR400 SDRAM modules just don’t work at their specified frequency with the ATI RADEON 9100 IGP, while others can only be used with loose timings. For example, the Corsair XMS3200LL memory we use often in our tests feels all right with Intel’s chipsets at 400MHz and with 2-2-2-5 timings, but is only stable in RADEON 9100 IGP-based mainboards with 2-3-3-8 timings. So, some problems with the memory controller in the North Bridge turn to be more persistent than expected and declared.

The North and South Bridges of the ATI RADEON 9100 IGP are connected via the proprietary A-Link bus that provides a bandwidth of 266MB/s. In its previous chipsets, ATI used to link the Bridges with the PCI bus, but its bandwidth is too low according to the today’s standards. The change of the bus also forced ATI to develop their own South Bridge called IXP250 (the previous chipsets from ATI came with South Bridges from ALi, but this trick is no longer possible).

The IXP250 South Bridge is scanty in its functions. My deepest sorrow was about the missing SerialATA/150 support: we have already got used to seeing it in modern chipsets. Seems like ATI has got some problems with this function, just like NVIDIA. Otherwise, the ATI IXP250 South Bridge supports six USB 2.0 ports, two ATA/100 channels and six-channel AC’97 audio. The network capabilities of the IXP250 are implemented by means of an integrated 3Com 10/100 Ethernet controller. Overall, ATI took it easy when developing this South Bridge. Some useful capabilities are simply missing, some are implemented by using third-party controllers. By the way, I have some reasons to think that the ATA/100 controller in the ATI IXP250 comes from Intel, too.