[openbeos] Re: posix compatibility -- brief history &overview
- From: "Daniel Reinhold" <danielr@xxxxxxxxxxxxx>
- To: openbeos@xxxxxxxxxxxxx
- Date: Mon, 11 Mar 2002 01:24:49 CST
Well, I'm no expert (and have never read a POSIX spec), but I'll take a
crack...
The original Unix was written largely in C for a specific mainframe
computer (PDP-7?) at Bell Labs in the early 1970's. It was mostly the
brainchild of Ken Thompson, who had also written an untyped, threaded-
code interpretive language called B. Dennis Ritchie took B, added
types, structs, and a few other things, and created C. In fact, C was
created mostly for the purpose of writing the new OS (which became
UNIX) in order to avoid having to use assembly language. The core of
the kernel was written in assembly, but the remainder (and majority)
was written in C. So it was somewhat portable.
When the mainframe at Bell Labs was upgraded to a new machine,
Thompson, Ritchie, et al, had to rewrite the OS and C compiler for the
new environment. Not finding this to be fun, they strove hard to design
the system so that it had the least possible depencies on the
underlying hardware. As the Unix system became popular and spread to
other research labs, universities, and organizations, the system had to
be ported many other times. It was decided to create a newsgroup to
foster the spread and standardization of this new sytem, which was the
start of Usenix.
Much of what was created was built on top of the initial ideas of Ken
Thompson. The notion of file descriptors and accessing devices thru a
simple common IO scheme was one of the hallmarks of Unix. Along with
this, the notion of pipes, redirection, hiearchical file systems, multi
-user access to shared resources, user/password logons, security, etc.
etc. (I'm sure I've left off many things) became standard across
implementations. The Usenix group encouraged both the spread of the
system and the standardization.
Eventually, Unix got big enough that it was decided to get serious
about standardizing the interface. Too many "slightly off" variations
of Unix were popping up: Irix, HPX, Aix, Solaris. POSIX was formed in
order to standardize what being a "Unix" really meant. No one could
claim to be Unix or Unix compatible w/o meeting the specifications of
POSIX.
The thing is, so many programmers over the years have cut their teeth
on Unix systems, that having POSIX compatibility is considered
desirable by any OS, even if it has another unique API of its own. For
example, I believe Windows NT (or 2000, whatever the hell it's called
these days) is POSIX compliant. But obviously, Windows is not Unix.
Being compliant means that programmers familiar with a Unix system can
be instantly productive on another platform. It's a hook to lure in
talent.
The BeOS was not fully POSIX compliant, as I understand, but had enough
to be familiar and usable to Unix types. For example, the BeOS has its
own file API with BFile, BDirectory etc. You can program using those.
Or you can use the classic C stdio interfaces fopen(), fread(),
fwrite(), fclose(), etc. Or even use the low-level, unbuffered versions
open(),read(),write(), close(). By having a POSIX layer, an OS does not
require prospective programmers to have to ditch everything they know
in order to become familiar with the new OS -- that would be a major,
killer hurdle. You can't underestimate the power and influence that 30
years of Unix culture has stamped on the programming community. A new
OS ignores POSIX at its own peril.
I'm surprised that Manuel stated that strcpy(), for example, was not
part of POSIX. I always thought that the entire standard C library had
to be hosted on a system in order for it be POSIX compliant. C and Unix
are historically very closely tied together. But I won't argue -- I'm
sure he knows much more about this than I.
Well, that's my overview explanation. I'm sure I've flubbed up on some
details, but I think the basic gist of it is correct.
>Whenever in doubt about an acroynm, ask Google "<acronym> webopedia"
>and click the first link :)
>
>http://www.webopedia.com/TERM/P/POSIX.html
>
>Considering I have no experience with it, someone else can fill in the
>details :)
>
>Andrew
>
>> i am very sorry for this newbie question, but i have read POSIX so
>> many times
>> now, but i still have no idea what its all about.
>> Since you you mentioned it in one sentence with ANSI C, its probably
>> a
>> programming standard, am I right?
>
>
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