Now that you have Lejos installed on your PC, the next thing you need to do is to install it into the RAM of the RCX. What you're going to do here is download the Lejos operating system files from the disk drive of your PC to the RAM of the RCX/brick.
If that sounds difficult - don't worry - it's easier than it sounds.
To download the Lejos operating system to the RCX, just follow these steps:
cd (change directory) to the directory containing the Lejos operating system files. On my system this is C:
\Java
\Lejos
\bin.
If the infrared tower is not already plugged into your USB port, plug it in.
Point the infrared tower at the top of the RCX/brick.
Make sure the brick is turned on. If it is not, press the On/Off switch to turn it on.
Enter this command to begin the download process:
\texttt{lejosfirmdl -f}
If the download fails with the "-f" option shown above, run it again without the "-f" option. (I have read in books and on other sites that the -f option does not work for them. BTW, "-f" stands for "fast".)
If everything works properly, you will hear a double beep sound, signalling that the software has been downloaded to the RCX. If you hear this, you are ready to start writing a first program.