Re: CDA vs. NDA vs. CDEV

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

In article <1993Dec11.052833.2177@leland.Stanford.EDU>
yucath@leland.Stanford.EDU (Cathay Kwok Tai Yu) writes:

[An excellent description of CDAs and NDAs]
>
> CDEV (I forgot what it stands for):

Originally, it meant "Control Panel Device".  Apple stopped calling
these programs "CDEVs" as of System 6.0.  They are now officially
called "Control Panels", and you use the "Control Panels" NDA to
access them (or directly, via the CDEVS folder, as you mentioned).

I don't know why they didn't rename the folder - it would have caused
too much confusion, I suppose.

> 	4)  Pros:  Very organized, very newish (full functionality only
> 		came with System 6, introduced in System 5)

They were pretty fully featured in System 5.0.  The "Control Panels"
NDA changed rather a lot in System 6.0, but it didn't affect the
individual Control Panels.  The difference is that System 5 brings up
a control panel in the same window as the scrolling list of control
panels; System 6 creates a separate window for each control panel, and
you can open several of them at once.

Control Panels are quite similar to NDAs, but even easier to write -
almost everything is handled by the Control Panels NDA.  There is one
minor catch in writing a Control Panel: you have to use resources (the
code and everything else associated with a control panel is stored in
the file's resource fork).

They are mainly intended for configuring the system in various ways.
Most of the Apple-supplied Control Panels modify various parameters in
the battery RAM and on the System disk.  Third-party Control Panels
are often used to configure other pieces of software (such as INITs)
or hardware, or provide extra system-level functions (as with
Pointless).


There is a lot of potential overlap between CDEVs, INITs and NDAs -
all of them can get control when the system starts up, and all of them
can patch themselves into the system in various ways (it takes a little
extra work to do this with a CDEV).
-- 
David Empson                                                               
dempson@swell.actrix.gen.nz                                                
Snail mail: P.O. Box 27-103, Wellington, New Zealand