quirkyjoe :
yes it is. I just now (1 minute ago) literally bought 4gb (2X 2GB) of the low density. $40.24 NEW! Just for the knowledge can both High & Low be used on the same board at the same time?
The density of the modules isn't important. What is important is ensuring that the modules are compatible with each other. I'm assuming that you wish to install the 2x2GiB that you just purchased alongside some existing 1GiB modules?
If so, problems with such a configuration are uncommon but not unheard of. There's no strict technical incompatibility, but mixing and matching memory can often cause instability. If you start to experience crashes, remove the older modules and make due with the 2x2GiB