I want to know which is the fastest storage medium like hd, fd, sd card.... to be used as virtual memory as my RAM is only 1GB and I didn`t want to spend too much on purchasing a new one.
If you are low on memory, there is nothing better than adding more RAM. Since RAM is so cheap, there is no reason not to get it. Crucial.com has a great memory advisor tool that can help you select the right memory. Their prices are good, but you can get better deals out there.
As for the other mediums, its impossible to say for sure. Paging memory requires both reading and writing to a medium. And every medium has different read and write speeds. Their ability will vary based on their specs, as well as your machines specs.