RCS and SCCS (and CMS)

[Doug Landauer]

In article <1134 at cod.NOSC.MIL>, dberg at cod.NOSC.MIL (David I. Berg) wrote:
> Another feature of RCS is that it stores the current
> version of your file and the changes backward to the original, whereas
> SCCS stores the original version of your file and the changes forward
> to the current.

This is a common misconception (oversimplification) -- it implies that
it could take significantly longer using SCCS to get the current
version of the file than for it to get the original version.  In fact,
SCCS does not store separate deltas; it stores all of the deltas
together, in the appropriate places within "the original file", in the
file in such a way that it takes about the same amount of time to get
any version.

There are several barely relevant performance implications of the
differences between this scheme and what RCS does:

    + for RCS:  For retrieving the latest version (RCS is betting that
	this is the most common case), RCS is likely to be faster;

    ~ :  For retrieving any other versions, RCS slows down relative
	to its own performance on the latest version (and at some point
	depending on how many deltas as well as how many lines changed
	per delta, it may be slower than SCCS);

    + for SCCS:  Doing RCS check-ins (storing new versions) should be
	distinctly slower than doing SCCS deltas;

> I find RCS particularly easier to use than SCCS.

I personally agree with this statement (disclaimer:  Sun doesn't
officially agree).  The BSD "sccs" front-end command helps some.

Finally, the performance differences mentioned above probably add up
(over the course of my entire SCCS career) to less time than I spent
composing this message (as David I. Berg put it, "it will take SCCS a
trifle longer"), so the ease-of-use factor should become the overriding
factor if you're starting a new project in a new company or on your
own.  In practice, the "what-they-use-here" factor is the real
overriding factor.

This is one of the few areas where VMS (gasp!) really does do better
than Unix (IMHO) -- DEC's CMS (though it has brain damage in some ways)
really does have some features that would make it, on the whole, better
than either SCCS or RCS, if you could use it on Unix instead of VMS.
--
	Doug Landauer				Sun Microsystems, Inc.
	ARPA Internet:	landauer at sun.com	Software Products Division
	UUCP:  ...!sun!landauer
--
Acronym glossary:   (Some of these are trademarks -- you know who you are.)
    BSD -- Berkeley Software Distribution
    CMS -- Code Management System (I think)
    DEC -- Digital Equipment Corporation
    IMHO -- In My Humble Opinion
    RCS -- Revision Control System
    SCCS -- Source Code Control System
    UUCP -- Unix-to-Unix CoPy
    VMS -- Virtual Memory System (an operating system for some DEC computers)
--