 This version was mounted in a rack mount case (thus the R) with considerably more RAM and a 32kB ROM which contained the parts of CP/M that were needed to boot the machine, so a disk was no longer required.Much of the additional RAM, up to 256kB of it, was dedicated as a RAM disk so the machines could be installed and left running for years – a floppy disk would burn out very quickly in this role.The additional RAM was not normally visible to the Z80 or the display hardware, but a new memory controller could switch in blocks of it so a number of screens could be cached if the disk needs were not that large.