The PDP-10 architecture is a family of 36-bit word-addressed machines.
They were manufactured primarily by DEC from 1964 to 1983, when they
were cancelled in favour of the VAX family.  Clones have been made by
Xerox, Foonly, Tymshare, Systems Concepts, XKL, and Neil Franklin.
Famous software first running on PDP-10s include: EMACS, ITS, WAITS,
SPELL, ADVENT?, Zork, Dungeon?, MacLisp.  Not first: TECO.

A memory word is 36 bits long, which is also the length of the
general-purpose registers.  All user instructions are 36 bits and have
9 bits to specify an operation, 4 bits to specify a register, 1 bit to
indicate indirect addressing, 4 bits to specify an index register, and
18 bits to specify an address or offset.  The first version of the
architecture was limited to a virtual address space of 256K words; a
later version extended this to a maximum of 1G words.
