Editing System programming language (section)

== History ==
The earliest system software was written in [[assembly language]] primarily because there was no alternative, but also for reasons including efficiency of object code, compilation time, and ease of debugging. Application languages such as [[FORTRAN]] were used for system programming, although they usually still required some routines to be written in assembly language.<ref name=Sammet>{{cite journal |last=Sammet |first=Jean |title=Brief Survey of Languages Used for Systems Implementation |journal=ACM SIGPLAN Notices |date=October 1971 |volume=6 |issue=9 |pages=1–19 |doi=10.1145/942596.807055|doi-access=free }}</ref>

===Mid-level languages===
Mid-level languages "have much of the syntax and facilities of a higher level language, but also provide direct access in the language (as well as providing assembly language) to machine features."<ref name=Sammet /> The earliest of these was [[Executive Systems Problem Oriented Language|ESPOL]] on Burroughs mainframes in about 1960, followed by [[Niklaus Wirth]]'s [[PL360]] (first written on a Burroughs system as a [[cross compiler]]), which had the general syntax of [[ALGOL 60]] but whose statements directly manipulated CPU registers and memory. Other languages in this category include [[MOL-360]] and [[PL/S]].

As an example, a typical PL360 statement is <code>R9 := R8 and R7 shll 8 or R6</code>, signifying that registers 8 and 7 should be and'ed together, the result shifted left 8 bits, the result of that or'ed with the contents of register 6, and the final result placed into register 9.<ref>{{Cite journal |last=Wirth |first=Niklaus |author-link=Niklaus Wirth |title=PL360, A Programming Language for the 360 Computers |journal=Journal of the ACM |date=1968 |volume=15 |issue=1 |pages=37–74|doi=10.1145/321439.321442 }}</ref>

===Higher-level languages===
While PL360 is at the semantic level of assembly language, another kind of system programming language operates at a higher semantic level, but has specific extensions designed to make the language suitable for system programming. An early example of this kind of language is LRLTRAN,<ref>{{Cite journal |last1=Mendicino |first1=Sam F. |last2=Hughes |first2=Robert A. |last3=Martin |first3=Jeanne T. |last4=McMahon |first4=Frank H. |last5=Ranelletti |first5=John E. |last6=Zwakenberg |first6=Richard G. |title=The LRLTRAN Compiler |journal=Communications of the ACM |date=1968 |volume=11 |issue=11 |pages=747–755|doi=10.1145/364139.364154 }}</ref> which extended Fortran with features for character and bit manipulation, pointers, and directly addressed jump tables.

Subsequently, languages such as C were developed, where the combination of features was sufficient to write system software, and a [[compiler]] could be developed that generated efficient object programs on modest hardware. Such a language generally omits features that cannot be implemented efficiently, and adds a small number of machine-dependent features needed to access specific hardware abilities; [[inline assembly]] code, such as C's {{code|lang=c|asm}} statement, is often used for this purpose. Although many such languages were developed,<ref name="MOHLconfer"/> C and [[C++]] are the ones which survived.