Hi MTCAT
 ... However, for the extension that's being loaded, either the 486 or 686 package, as specified in onboot.lst, where are the files associated with that package being placed ?
Extensions are compressed read-only file systems (squashfs). They get mounted under  /tmp/tcloop  but the extension
itself lives in the  tce  directory of your disk drive. Once installed, you can look in  /tmp/tcloop/24dsi-2.6.33.3-tinycore-686
and you will find it contains  usr/local/lib/lib24dsi_api.so  which is linked into the main file system as  /usr/local/lib/lib24dsi_api.so.
Note the leading slash in that second path. If you execute this:
ls -l /usr/local/lib/lib24dsi_api.soit's going to indicate that it is a link that points back to  /tmp/tcloop/24dsi-2.6.33.3-tinycore-686/usr/local/lib/lib24dsi_api.so.
The rest of the files in the extension get linked into their respective locations in the main file system.
 ... Just wondering, to automatically load the 24dsi driver, I'm thinking I could add the following to bootlocal.sh ? 
For the 686 driver (for the DX3),
sudo /home/tc/24dsi.linux.4.11.91.32.0/24dsi/driver/start ... 
That's just the startup script for loading the driver and creating device nodes in  /dev.
You still need to place the driver in the correct location and run  depmod  to update the driver database for the OS.
You still need to place the library in the correct location and run  ldconfig  to update the library cache for the OS.
You still need to place the utility programs where the OS can find them so you don't have to keep typing a path.
With the extension you create the correct locations for the various libs, drivers, programs, etc.
tce-load handles running  depmod  and  ldconfig.
If you are booting, it runs them after it's loaded everything in  onboot.lst to save time.
The alternative is copying the files to  /us/local/bin, /usr/local/lib/, etc.  and running  depmod  and  ldconfig  yourself.
/usr/  is located in RAM. As a result, those files will occupy their size in RAM. As an extension, they only get linked in
and occupy around 30 to 60 bytes of RAM.