A SCSI controller which attaches to the side expansion slot, originally intended for use with the A1000 it probably works with the A500/+ too. There is enough room inside the unit to mount 2 SCSI hard disks and may have been shipped with 2 x 50MB disks by default. The unit is bootable under Kickstart 1.3 and newer, it has a pass-through for other devices and an external DB25 SCSI connector. There is no facility for adding additional RAM.
Thanks to Sebastian Kinner