The ISE is needed to mount the DSSI disk. VAX 4ks in the BA4(30/40) have a sled arrangement with a card edge connector bringing out power and DSSI. I've been looking for one for a while, and most of the E-Bay DSSI drives are stripped from the sleds (don't know why, I guess earlier MicroVAXen didn't use the sleds). The KZQSA will work in a pinch provided that you want to run VMS, none of the xBSDs offer support for it (ULTRIX doesn't even work well with it) Performance will likely leave something to be desired. I've seen docs for a HSD that mounts in the BA4x0 and allows for SCSI in the upper bay, but have not seen one in the flesh. I'm currently looking to wire a HSD05-AA SBB in mine, but it still looks like I need a sled or two for mechanical connections :(.