HP48 Calculator

<< "HELLO WORLD" HELLO >>
'HELLO' STO

Also, the program above for the HP48 calculator will (unfortunately) put
"HELLO WORLD" on the stack until the calculator runs out of memory.  To
make it less dangerous, the first line (the program itself) could be changed
to
<< DROP "HELLO WORLD" HELLO >>
Unfortunately, this has the side effect of removing whatever you had on
the stack if you left anything on it, and it crashes if the stack is empty.
To rememdy this, before executing, put a 0 or some other useless number on
the stack.  Otherwise, use the first program and cancel it before you run
out of memory.

I'm surprised nobody else has submitted this: here's a User-RPL
program to print "Hello world!" forever.  The repetition is not
particularly impressive because the text is always printed in the same
place.

(User-RPL is the higher-level HP48 programming language.  It is also
possible to program in Sys-RPL, which is assembly language.  In case
the program is mangled, I should tell you that its first line is an
opening guillemet and its last line is a closing guillemet.)

´ 
    WHILE 1 
    REPEAT 
	"Hello world!" 0 DISP
    END
ª