A minicomputer sold by DEC in 1964. It had a memory cycle time of 1.75 microseconds and add time of 4 microseconds. I/O included a keyboard, printer, paper-tape and dual transport DECtape drives (type 555).
DEC provided an "advanced" Fortran II compiler, a Symbolic Assembler, Editor, DDT Debugging System, Maintenance routines and a library of arithmetic, utility and programming aids developed on the program-compatible PDP-4.
[DEC sales brochure].
The PDP-7 was considered reliable enough (when properly programmed) to be used for control of nuclear reactors and such.
Around 1970 Ken Thompson built the operating system that became Unix on a scavenged PDP-7 so he could play a descendant of the SPACEWAR game.