SCSI Control question

[alejack12001]

My inquiry to to ask about the sequence of a MS-DOS boot with regard to a SCSI drive being internal or external connected to the controller. What I am asking is that If the SCSI drive is set to SCSI ID 0 or 1 then the location shouldn’t make a difference. I wanted to see if that concept is correct. Will the computer try to boot for the internal drive first if the SCSI ID is not SCSI ID 0 or 1 then seek the external drive if that drive is 0 or 1 or give me an error that it cannot find the boot disk?

 

[Timo W.]

SCSI has no idea if a device is internal or external. It's all the same bus. If the controller is set to boot from ID 0, it will always do that.

 

[g4ugm]

That depends on the controller. If the controller is only a single SCSI bus then even the card has no idea if the disk is internal or external. If its two SCSI Busses then it could be a setting in the SCSI BIOS or hard coded.

 

[Chuck(G)]

Yup. E.g. Adaptec 2985 or 3940. Multiple controllers on a card.

 

[alejack12001]

The controller is the Adaptec 1522 that I wrote about in a previous post. The users manual doesn't specify whether the controller is single or multiple. Right now I am assuming single. If this controller is single then only one terminator would be needed, correct or not?

 

[Chuck(G)]

Yes, the 1522 is a single controller (not my favorite ISA version). Each end of a SCSI chain requires a terminator. Thus:
term->drive->cable->controller<-cable<-drive<-term (with the terminator on the controller disabled)

 

[alejack12001]

Yes, the 1522 is a single controller (not my favorite ISA version). Each end of a SCSI chain requires a terminator. Thus:
term->drive->cable->controller<-cable<-drive<-term (with the terminator on the controller disabled)

That is good to know, I couldn't find anthing in the SCSI book I have, Version 2 regarding the removal of the controller terminator. Now, I can see the end to end terminators. This make sense.