The very first IBM PC had from 512K to 640K of RAM. That was back in the early 80'
My Apple ][ had 48K about 5 years before that.
Now, you can'find any computer with less than 512M, or 1024 times as much. A modern computer with only 56K of RAM, even 128K, won't even boot.
Do you mean a 56k MODEM?
If so, it will work correctly, it's just your internet connection that will be rather slow by todays standards. The computer's speed will unaffected.
Kualinar, March 2010