Hello,
It is possible to destroy a disk drive, or completely make your machine unusable.
One thing to watch for is disk drive motors. If you forget to stop them after an operation, it is possible that it could wear out.
Directly probing memory for any reason can cause unpredictable damage depending on what location, and in what way.
Also, there are some 'holes' in physical memory that you need to be very careful of. More specifically, memory above 1MB.
Their are more. Just be careful and
insure you are setting and know exactally what it should do.
Testing your software on an emulator is a great way that may resolve most possible problems.
Also, get the memory map from the BIOS to insure you get the correct amount of RAM, and locations that you can safely touch. Only do this when you are ready, however. (i.e., do not worry about it until later when you get to the kernel.)
The tutorial demos are completely tested on real hardware, and does work fine.
From all of the tutorials thus far, the only hardware damage that can be done is destroying your floppy drive, or the memory problems discussed above.
Tutorial 7 contains the basic memory map layout for memory below 1MB. As long as you read or write to the unused portians of the memory map, everything should be fine.
