In the 1960s and 1970s, some computer manufacturers, such as IBM,
Digital, and Burroughs (now UNISYS), developed special machine-oriented
high-level languages for systems software on their machines. For IBM main-
frame computers, the language was PL/S, a dialect of PL/I; for Digital, it was
BLISS, a language at a level just above assembly language; for Burroughs, it
was Extended ALGOL. However, most system software is now written in more
general programming languages, such as C and C++.