It depends on what you mean by "shared".
Only two devices can communicate at a time on a SCSI bus. So at any given moment, the bandwidth is not shared. It is all devoted to the channel between the two devices (usually the host controller and a device) which are currently communicating.
Further, SCSI devices have a priority ranking based on their SCSI ID, which determines which devices get control of the bus, if multiple devices are trying to talk at the same time.
SCSI ID 7, usually the host controller, always has the highest priority. From there, highest priority is ID 6 and descends to 0. If the SCSI bus is a wide bus with IDs from 0 - 15, then the previous statement is still true, but after SCSI ID 0, ID15 has the next priority and descending from 15 to 8.
Of course, if you have an array of disks, all on the same SCSI bus, and a controller scheme which gives them all about equal usage, then it will look a lot like the bus is dividing its bandwidth evenly amongst them all.
Only two devices can communicate at a time on a SCSI bus. So at any given moment, the bandwidth is not shared. It is all devoted to the channel between the two devices (usually the host controller and a device) which are currently communicating.
Further, SCSI devices have a priority ranking based on their SCSI ID, which determines which devices get control of the bus, if multiple devices are trying to talk at the same time.
SCSI ID 7, usually the host controller, always has the highest priority. From there, highest priority is ID 6 and descends to 0. If the SCSI bus is a wide bus with IDs from 0 - 15, then the previous statement is still true, but after SCSI ID 0, ID15 has the next priority and descending from 15 to 8.
Of course, if you have an array of disks, all on the same SCSI bus, and a controller scheme which gives them all about equal usage, then it will look a lot like the bus is dividing its bandwidth evenly amongst them all.