Editing VAX (section)

=== SIMACS ===
''[[System Industries]]'' developed an ability to give more than one DEC CPU, but not at the same time, write access to a shared disk. They implemented an enhancement named [[SIMACS]] (simultaneous machine access),<ref>{{cite web |url=http://www.atnf.csiro.au/observers/memos/d95f80~1.pdf |title=Computing Requirements for AT Software Development |last1=Wand |first1=R. |last2=Kesteven |first2=M. |last3=Rayner |first3=P. |date=February 24, 1984}}</ref><ref name=SIMACS.HC84>{{cite magazine |last1=Joshi |first1=Prem |last2=Delacroix |first2=Jacques |date=September 1984 |title=New Flexibility For Multiple VAX/VMS |magazine=[[HARDCOPY]] |pages=64–68}}</ref> which allowed their special disk controller to set a [[Semaphore (computing)|semaphore flag]] for disk access, allowing multiple WRITES to the same files; the disk is shared by multiple DEC systems. ''SIMACS'' also existed on PDP-11 [[RSTS/E|RSTS]] systems.