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The self-timed interface (STI), used in several generations of IBM's most powerful servers, has evolved to provide a greater I/O subsystem bandwidth than ever before. The STI of the IBM eServer z900 is capable of transferring data between the processor complex and the I/O subsystem at a rate of up to 1 GB/s compared with the 333MB/s rate of the IBM S/390® G3/G4- and G5/G6-class large servers—an improvement of up to a factor of 3. Additionally, in the eServer z900, STI links suitable for transferring data at a rate of 1 GB/s are used for the third iteration of the integrated cluster bus (ICB-3), thus providing direct links to other eServer z900s. Also, the role of the STI has increased in the eServer z900, becoming the interface used on the I/O subsystem backplane. The majority of the STI logic (both physical and logical layers) has remained essentially unchanged, with advances resulting from the use of improved cables and connectors, and from the introduction of a multilevel, pre-distortion differential off-chip “super-driver.”
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