[p_l]

Main cases I've seen with mainframes involved network-attached ram disks (actually, even earliest S/360 could share a disk device between two mainframes, so...)

A fast scratch pad that can be shared between multiple machines can be ideal at times.

[rbanffy]

Makes sense in batch environment - you can lock the volume, do your thing, and then freeing it to another task running on a different partition or host.

Still seems like a kludge - The One Right Way to do it would be to add that memory directly to a CPU addressable space rather than across a SCSI (or channel, or whatever) link. Might as well be added to the RAM in the storage server and let it manage the memory optimally (with hints from the host).

[p_l]

There was no locking (at least not necessarily), it was a shared resource that allowed programs on multiple computers to utilize together (also major use case for RAMsan where I worked with them - it was not about not being able to add memory, it was about common fast quorum and cache between multiple maxed out database servers)