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Path: euryale.cc.adfa.oz.au!newshost.carno.net.au!harbinger.cc.monash.edu.au!news.mel.connect.com.au!munnari.OZ.AU!news.ecn.uoknor.edu!feed1.news.erols.com!howland.erols.net!news-peer.gsl.net!news.gsl.net!news-stkh.gsl.net!news.gsl.net!nntp-oslo.UNINETT.no!nntp-trd.UNINETT.no!not-for-mail From: sthaug@nethelp.no (Steinar Haug) Newsgroups: comp.unix.bsd.freebsd.misc Subject: Re: NCR or Symbios SCSI Controller Date: 22 Dec 1996 08:45:06 GMT Organization: Nethelp Consulting, Trondheim, Norway Lines: 39 Message-ID: <59isei$i52@verdi.nethelp.no> References: <32B5B05F.77E0@zedat.fu-berlin.de> <E2q37p.L4L@cogsci.ed.ac.uk> <59hi7m$fq3@verdi.nethelp.no> NNTP-Posting-Host: aun.uninett.no In-reply-to: sthaug@nethelp.no's message of 21 Dec 1996 20:44:38 GMT Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:32848 [Steinar Haug] | I believe the original poster is at least partly correct. As far as I | know, the NCR/Symbios 53c810 and 53c815 SCSI processors have to fetch | all the SCSI 'SCRIPTS' commands across the PCI bus, while the 53c825 | and 53c875 SCSI processors have 4 kByte of static RAM for storage of | 'SCRIPTS' commands on chip. | | Thus for instance the ASUS SC200, which is based on the 53c810, will | indeed use *some* bus bandwidth. I have no idea just how much - maybe | Stefan Esser can tell us? Here is a reply from Stefan Esser. He says that he normally doesn't have time to read USENET. He reads the FreeBSD mailing lists though, e.g. FreeBSD-SCSI@FreeBSD.Org for SCSI questions. Steinar Haug, Nethelp consulting, sthaug@nethelp.no #------------------------------------------------------------------- The NCR does in fact read instructions from DRAM, just like any other CPU in a multi-processor system does. And the NCR does in fact contain a small CPU, which offers 8bit arithmetic operations, but also quite complex SCSI transfer operations in its instruction set. The instruction set allows to transfer one page worth of data (ie. 4KB) with only 2 NCR instructions, and thus the overhead for the actual data transfers is rather low. My estimate is, that instruction fetches add a few percent over the bandwitdh required just for the data transfer, unless very small transfer sizes are used. The newer WIDE chips offer an on-chip 4K SRAM, which can hold the NCR firmware, and there are drivers that take advantage of the SRAM. The current NCR driver doesn't, but still offers much better system throughput than other drivers, that do :) (I've seen the Bonnie results on identical hardware.) If your system is a highly loaded server with multiple SCSI cards, then you may be better off with AH2940 controllers, but if you got a single SCSI card, then the NCR will do as well and will be much cheaper.