Re: CDA,NDA question

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <4ffjdv$69b@news.ysu.edu>,
Adalbert Goertz <be404@yfn.ysu.edu> wrote:
> 
> What is the difference between CDA and NDA?

CDA = "Classic Desk Accessory".
NDA = "New Desk Accessory".

A Classic Desk Accessory is a text-based accessory (usually - a small
number work in graphics mode) that appears under the "Desk
Accessories" menu accessed using Control-Apple-Escape.  The text-mode
Control Panel is an example of a CDA that is built into the computer's
ROM.  Most CDAs are able to be used in ProDOS-8 as well as GS/OS.  A
few which depend on the operating system will only work in one
environment.

A CDA takes over the computer's execution while it is running.

A New Desk Accessory is a graphical accessory that appears under the
Apple menu in desktop programs.  They can only be used in GS/OS
desktop programs.

An NDA can share execution (cooperative multitasking) with other NDAs
that are open and the active desktop program.

> Do some of them work for certain GSOS versions only?

Yes.  In general, IIgs programs (including applications, INITs, CDAs
and NDAs) are written to be compatible with a particular version of
the operating system, and remain compatible with later versions.  Most
programs will not work with a version of the operating system which is
too old.

System 6.0 added quite a lot of new features, and there are many
programs that require 6.0 or 6.0.1.  There are also some programs that
depend on new features provided by System 6.0.1, which will not work
with older versions.

There are a few programs (such as HyperCard IIgs) which require one
version of the operating system and will take advantage of special
features provided by a newer version.  HyperCard requries 5.0.4, but
will use some features of System 6.0 if it is present.  (It doesn't
know about 6.0.1, but still works with it.)

There are also a small number of cases where programs are not
compatible with newer versions of the operating system and/or ROM.
This is most likely in cases where the program has relied on some
undocumented feature to pull a special trick, and the underlying
mechanism was changed in a later version of the operating system.

An example of this is the first version of AnimWatch, which didn't
work on a ROM 3.  A patched version was released which worked on both
machines.

Another example of an incompatiblity is SoftSwitch from Roger Wagner
Publishing.  It has two CDA files, one of which provided the actual
CDA and the other patches the Desk Manager to add some features to the
CDA menu, allowing quick access to SoftSwitch.

Apple replaced the CDA menu in System 6.0, and the SoftSwitch patch
was broken.  I was still able to make use of SoftSwitch by avoiding
the use of the second CDA (SoftSwitch.INIT).
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand