SRFERGU%ERENJ@PUCC.PRINCETON.EDU (Scott Ferguson) (01/23/91)
I was thinking that I could connect two computers via their SCSI controllers and set up a nice high-speed data link. Now, as I learn a little more about SCSI, I'm finding it might not be possible: Supposedly, SCSI is set up to have a talker and a listener, much like IEEE-488 GPIB systems. However, talkers can't be made into listeners, because the hardware for each is different. A talker is a 'controller', and a listener is a 'host adapter'. Has anyone ever gotten a SCSI controller (talker) to act as a device/listener? If this isn't possible, why don't the people inventing these standards think a little farther ahead to more than just hard disks and tape drives? Thanks, Scott Ferguson srfergu@erenj.bitnet
israel@mitisft.Convergent.COM (Paul Israel) (01/25/91)
In article <9101231354.AA02134@umix.cc.umich.edu> SRFERGU%ERENJ@PUCC.PRINCETON.EDU (Scott Ferguson) writes: > >I was thinking that I could connect two computers via their SCSI controllers >and set up a nice high-speed data link. Now, as I learn a little more about >SCSI, I'm finding it might not be possible: > >Supposedly, SCSI is set up to have a talker and a listener, much like IEEE-488 >GPIB systems. However, talkers can't be made into listeners, because the >hardware for each is different. A talker is a 'controller', and a listener >is a 'host adapter'. > I think the terms you're groping about for are "initiator" and "target". The initiator is usually associated with the host system, and is responsible for initiating a transaction with some peripheral controller. The peripheral end is the target, and is the one which actually generates the necessary handshakes to transfer the data. Normally, this relationship is static, although some targets can become initiators to other targets for the purposes of performing direct peripheral-to-peripheral copy procedures. While it may be more expensive, the simplest solution for what you have in mind would be to provide each system with two SCSI interfaces on the same bus. Each system would attach to one SCSI interface as an initiator, and to the other as a target. This would permit you to hook up as many as four separate systems on one bus in this many. Keep in mind, though, that there would be an implied bus request priority fixed among the systems, based on the SCSI address assigned to them. If you want to set up a dedicated high speed link between two systems, you could again use two SCSI interfaces per system, but interconnect them with TWO busses instead of one. That way, each bus would consist of a target from one system and an initiator on the other. Each would have exclusive and immediate control of a bus to transfer data to the other. While being very high speed, it is not, however, very economical, or leave much room for expansion (although you could use the remaining addresses on each bus for normal peripherals for each system). -- Paul Israel Renegade Systems, 434 South Bernardo Ave, #2 Sunnyvale, CA 94086 Disclaimer: "Who, me? I wasn't even there!" ctnews!mitisft!hamster!israel