Comment by snvzz

Since AmigaOS 1.3 (1987), Amiga has had a software version of a block device in memory which survives reboot, called "ramdrive.device", and usually mounted on DOS as "RAD:". It can even be a bootable device.

This is in addition to the, available since earlier, "Ram-Handler", a filesystem similar to Linux's ramfs, which does not survive reboots.