Re: Who needs files?

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1 total messages Started by darrell Fri, 27 Mar 1987 02:02

#120

Author: darrell
Date: Fri, 27 Mar 1987 02:02

29 lines
1976 bytes

>In article <2859@sdcsvax.UCSD.EDU> johnl@ima.ISC.COM (John R. Levine) writes:
>>In article <2850@sdcsvax.UCSD.EDU> bagwill@decuac.DEC.COM (Bob Bagwill) writes:
>>>
>>> ... Why not define all storage as extended memory structures
>>>that may be loaded as needed.  ...
>>
>> ... it makes device independence very hard. ...
>>
>>The other reason that you want files is that they have an existence and a
>>naming structure separate from the programs that manipulate them, which is
>>kind of unavoidable.  You as a human would probably rather call a file
>>/usr/fred/games/source/pinball_bounce.c, while your program would rather
>>have a nice handle like a memory address of 0x18723d70 or a file handle of 5.

Actually, there are operating systems that let you do this sort of
thing.  (Well, maybe it's just a sufficiently close approximation.)
The Dartmouth College Time Sharing system provides an "address file"
system call which maps a file into your virtual memory space.  The
program now has a nice handle on the file which is a memory address,
the operating system having performed the translation between a user
supplied treename (pathname) and a memory address.

The program can now access the memory mapped file using a suitable
data structure.  Device independence is not a problem.

Back before DCTS implemented this system call, some people were porting
IBM PL1 programs which apparently did similar things.

-- Chuck

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