Date: Tue, 25 Feb 1997 20:52:37 -0500 From: Matt Thomas <matt@lkg.dec.com> To: "Jin Guojun[ITG]" <jin@george.lbl.gov> Cc: freebsd-hardware@freebsd.org Subject: Re: Memory speed of P6-200 (256k) Message-ID: <3.0.32.19970225205045.006884cc@netrix.lkg.dec.com>
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At 03:53 PM 2/25/97 -0800, Jin Guojun[ITG] wrote: >} At 12:48 PM 2/25/97 -0800, Jin Guojun[ITG] wrote: >} >The PCI is a 64-bit wide bus. The maxmimum memory speed you can get from >} >this bus is 1000000000 * 8 / 60ns = 133333333 Bytes/sec (no inteleave). >} >} That is wrong. The PCI is typically a 32-bit wide bus running @ up to 33Mhz. >} >} 4 bytes * 33Mhz = maximum of 132MB/s assuming almost perfect bursting >} and no wait states. >} >} 64 bit PCI doubles that maximum to 265MB/s. > >That is the PCI bus bandwidth, not the memory bandwidth :-) >PCI != MEOROY, but main memory uses PCI bus. The main memory access may be done through a PCI host bridge, but that does not mean that's it done through the PCI. A system/cpu may have more than one PCI bus (like Alpha's or high-end Pentium Pro's). Memory bandwidth is not directly related to PCI bandwidth. -- Matt Thomas Internet: matt@3am-software.com 3am Software Foundry WWW URL: http://www.3am-software.com/bio/matt.html Westford, MA Disclaimer: I disavow all knowledge of this message
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