Most older computers have very small hard drives.

If anyone actually uses your donated computer, they would probably put in a newer bigger one anyway.

And Jo is right, about the RAM. I'd leave it. Today RAM is very inexpensive, and the size of the clips is tied to the type of computer you have and not interchangeable easily with others.

Basically if you remove the harddrive, the only things left are the motherboard with the working chip and your sound/video card.

I'd keep the hard drive myself. Some day you might want to retrieve the data.

Ask where you donate it ... how it will be used. I would think it would be taken apart for parts, as a likely scenario. My son used to do that, and rebuild new ones. Schools etc may use a donated one that way.