<The floppy disks are 8" RX01 compatible drives. The interesting thing is <that this device can format the disks, not by some special format command <procedure... it formats a sector when it writes it... It happens to use a 1773 floppy controller that can format, there is also local ram and an 8085 micro to make the disk appear smarter. <The on-board ROMs know about RT-11 Queue elements, so the RT driver <simply calls the ROM to handle the I/O, and the ROM returns if there <was an error, or when the request is complete. Between the Disk system with it's 8085 and the DL compatable IO that also has its own 8085 Plus either 3 ot 6 2651 usarts) it's easy to see how the system is smarter in some places. for a small system that makes it unique for it's time. The same basic bard set was used in the PDT-11/110(MOP loaded) and 11/130 (TU58 tape) the main difference was the use of TU58 (unique with a parallel interface) and some minor rom level code to boot it. <I don't know of anything else which ever ran on it... (I would be <interested to know if there ever was). I head someone had COS running in it. In theory is a vanilla 11/2 with 28KW of ram and a series of DL ports and a mass storage device that is sorta RX01(two 256k floppies RX01 format). Unless you used DDCMP to another system storage would be the limiting aspect. NOTE: expansion is not possible, there is no externally acccessable bus or expansion port. I have the PDT11/130 version and several boards for PDt150/130 as spares. Allison