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Your PC's Second Most Important Silicon: The Chipset October 30, 2002 Why Some Systems Work Better Than Others If the CPU is the brain of a personal computer, the motherboard is its nervous system -- the foundation or platform that supports and provides the data-transfer connections between the processor, memory, AGP and PCI expansion cards, disk drives, and external peripherals. And next to the CPU, the most important part of a motherboard is its core logic chipset. One manufacturer, Nvidia Corp., prefers the term "platform processor" to "chipset." It's marketing jargon that makes sense, in that a chipset determines a motherboard's and hence computer's capabilities -- everything from what kinds of peripherals you can plug into it to what kinds of CPU and memory it can use. Nowadays, thanks to TV commercials, even casual home-PC buyers are likely to ask which processor a system has. This article will explain why truly smart shoppers learn which chipset it has, too. North and South A chipset's functions are divided into two groups, which are usually handled by two chips -- the Northbridge and Southbridge, which you can think of as "inner" and "outer" or adjacent to the CPU and peripherals, respectively. Names vary -- Intel calls these components hubs; SiS calls them controllers -- but the purpose is the same: the Northbridge and Southbridge provide data bridges between specific sets of bus peripherals. Intel's block diagram of its recently introduced 845PE Pentium 4 chipset, reproduced below, illustrates the architecture of most standard chipset designs -- the Northbridge handling the more data-intensive pathways such as the memory and AGP (Advanced Graphics Port or screen display) buses, while the Southbridge takes care of secondary connections such as those to ATA/IDE disk drives and USB peripherals. There is a strict division of duties between the Northbridge and Southbridge, as well as a high-speed interface between the two. As an alternative, some vendors such as SiS have created single-chip designs (see the SiS 745 chipset diagram below), putting both Northbridge and Southbridge functions on a single die. At least in theory, this has obvious benefits, such as lower production costs (for potentially cheaper motherboards) and the fastest possible communication between Northbridge and Southbridge components. It also has obvious disadvantages, such as the need to create a totally new chipset design just to add one new Southbridge feature (upgrading from USB 1.1 to USB 2.0 support, for instance). Whether for these reasons or simply for the sake of playing by the standard rulebook, SiS' more recent 746 Athlon XP chipset went back to the dual-chip design -- using, in fact, the same 963 Southbridge as the company's SiS 648 Pentium 4 chipset.