The RT-11 operating system could be stored on a 2.5mb removable hard disk platter. Or it could be booted from a 8 inch floppy disk. The system could support a real time clock, printing terminal, VT-11 vector graphic unit, 16 channel 100khz A/D converter with 2 channel D/A, a serial port 9600 baud, 16 bit bidirectional boards, etc. The file system used an 8.3 file name format. An assembly language and a FORTRAN compiler were available from DEC.
Later when DEC introduced the LSI computers, they were able to run RT-11 from an 8 inch floppy disk. Several years later, DEC introduced RSX-11. RSX-11 was a multiuser, multitasking operating system. RT-11 remained the operating system of choice for data acquisition systems where real time response was required.
RT-11 also ran on DEC-10s. It was run on DEC 11/34s to DEC 11/60s. It also ran on the PDT-11.
S&H Computing developed TSX-Plus OS, which is essentialy a multi-user, multi-processing extension of RT-11.