On Dec 4, 2018, Greg 'groggy' Lehey
<grog(a)lemis.com> wrote:
The original Tandem OS (called Guardian at the time) was written in Tandem's TAL
(Transaction Application Language, amongst other productions), a vague evolution of
HP's SPL that looked more like Algol, starting in about 1974. That is also the
earliest I know of an operating system being implemented entirely in a high level
language.
Most likely the earliest operating system written in a high-level language was the one for
the Burroughs B5000 (early 1960s), written in a dialect of Algol 60. Others: Multics,
written in PL/1 (starting in mid 1960s), the operating system for the Berkeley Computer
Corporation’s BCC-500, written in BCC SPL (system programming language) (late 1960s), OS6
by Stoy and Strachey, written in BCPL (early 1970s), Xerox Alto OS, written in BCPL (about
1974).