Date: Wed, 30 Dec 1998 13:10:22 -0500 From: Graeme Tait <graeme@echidna.com> To: Joe Gleason <clash@tasam.com> Cc: freebsd-hardware@FreeBSD.ORG Subject: Re: Motherboard with onboard scsi Message-ID: <368A6C8E.4528@echidna.com> References: <010501be340d$7f0f4940$f1effccd@bug.tasam.com>
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Joe Gleason wrote: > > I am looking at motherboards with on board scsi for a server I am building. > > On the Asus page for the P2B-DS it lists: > Adaptec ® AIC 7890 & 3860 80MB/s Ultra2 Wide SCSI Onboard (AIC 3860 Optional) > > Most other motherboards I see (Tyan, IWill, Supermico) > Have only either a AIC7890 or AIC7895 with no mention of 3860 The 3680 transceiver allows there to be two high speed buses, one fast-wide, one ultra-2 LVD. There are actually 3 SCSI connectors on the Asus P2B-S motherboards I have: one 50-pin fast SCSI, one 68-pin fast-wide, one 68-pin ultra-2 LVD. My understanding is that without this chip and using the 7890, if you mix fast-wide and ultra-2 LVD devices on the wide SCSI bus, the bus collapses to fast-wide mode, and LVD (low-voltage differential) devices are forced to switch to single-ended mode, transferring at 40MB/s. With the 3860, you have two separate busses, one for fast-wide devices at 40MB/s, one for ultra-2 LVD devices at 80MB/s (in 16-bit mode). Obviously this only matters if you intend to use ultra-2 LVD devices. The LVD bus also supports longer cable lengths, although the cabling I received with the Asus P2B-S board provides for internal LVD devices only. The cable for the fast-wide bus does provide an external wide SCSI connector. > What is the difference between 7890 and 7895? This I don't know. You might want to peruse Adaptec's website. -- Graeme Tait - Echidna To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hardware" in the body of the message
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