[Discuss-gnuradio] why some components are skipped?

[zhifeng]

Hi,
When I install GNU Radio in Ubuntu 7.04, after ./configure, there are
some components skipped. I follow the wiki strictly in gnuradio.org and
find some other people also have such issues, but I can't find answer for:
1. What is the reason these components are skipped? 
2. whether it may impact the followed "make" command and normally usage
of GNU radio later?

I try to read configure.ac, but still don't understand. My computer
configuration as below, by uname:
Linux james-desktop 2.6.20-16-generic #2 SMP Thu Jun 7 20:19:32 UTC 2007
i686 GNU/Linux

here is log:

*********************************************************************
The following GNU Radio components have been successfully configured:
 
config
omnithread
gnuradio-core
pmt
mblock
usrp
gr-usrp
gr-audio-alsa
gr-audio-oss
gr-atsc
gr-cvsd-vocoder
gr-gsm-fr-vocoder
gr-pager
gr-radio-astronomy
gr-trellis
gr-video-sdl
gr-qtgui
gr-wxgui
gr-sounder
gnuradio-examples
 
You my now run the make command to build these components.
 
*********************************************************************
The following components were skipped either because you asked not
to build them or they didn't pass configuration checks:
 
gr-audio-jack
gr-audio-osx
gr-audio-portaudio
gr-audio-windows
gr-comedi
 
These components will not be built.