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A northbridge or host bridge is one of the two chips in the core logic chipset architecture on a PC motherboard. Unlike the southbridge, northbridge is connected directly to the CPU via the frontside bus (FSB) and thus responsible for tasks that require the highest performance. The northbridge is usually paired with a southbridge, also known as I/O controller hub. In systems where they are included, these two chips manage communications between the CPU and other parts of the motherboard, and constitute the core logic chipset of the PC motherboard.〔(【引用サイトリンク】url=http://www.pcmag.com/encyclopedia/term/48076/northbridge )〕 On older Intel based PCs, the northbridge was also named external memory controller hub (''MCH'') or ''integrated memory controller hub'' (''IMCH'') if equipped with an integrated VGA memory controller hub (MCH). Increasingly these functions became integrated into the CPU chip itself, beginning with memory and graphics controllers. For Intel Sandy Bridge and AMD Accelerated Processing Unit processors introduced in 2011, all of the functions of the northbridge reside on the CPU, while some high-performance CPUs still require northbridge and southbridge chips externally. Separating the different functions into the CPU, northbridge, and southbridge chips was due to the difficulty of integrating all components onto a single chip. In some instances, the northbridge and southbridge functions have been combined onto one die when design complexity and fabrication processes permitted it; for example, the Nvidia GeForce 320M in the 2010 Macbook Air is a northbridge/southbridge/GPU combo chip.〔(The Macbook Air: A Sign of Things to Come – Digital Gravitas )〕 As CPU speeds increased, a bottleneck eventually emerged between the processor and the motherboard, due to limitations caused by data transmission between the CPU and its support chipset. Accordingly, starting with the AMD Athlon64 series CPUs (based on the Opteron), a new architecture was used where some functions of the north- and southbridge chips were moved to the CPU. Modern Intel Core processors have the northbridge integrated on the CPU die, where it is known as the uncore or system agent. ==Overview== The northbridge typically handles communications among the CPU, in some cases RAM, and PCI Express (or AGP) video cards, and the southbridge.〔George Jones - Maximum PC 2005 Buyer's Guide - Prentice Hall PTR - ISBN 0-7686-6312-1〕 Some northbridges also contain integrated video controllers, also known as a Graphics and Memory Controller Hub (GMCH) in Intel systems. Because different processors and RAM require different signaling, a given northbridge will typically work with only one or two classes of CPUs and generally only one type of RAM. There are a few chipsets that support two types of RAM (generally these are available when there is a shift to a new standard). For example, the northbridge from the Nvidia nForce2 chipset will only work with Socket A processors combined with DDR SDRAM; the Intel i875 chipset will only work with systems using Pentium 4 processors or Celeron processors that have a clock speed greater than 1.3 GHz and utilize DDR SDRAM, and the Intel i915g chipset only works with the Intel Pentium 4 and the Celeron, but it can use DDR or DDR2 memory. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Northbridge (computing)」の詳細全文を読む スポンサード リンク
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