ddr sdram or just sdram?

I just bought a dimension 4550 with 2.66 ghz and what I thought was 256 mg of ddr sdram, however when i go to the dell website and have their software check my computer's configuration it says I have 256 mg sdram.  I had my friend who had recently purchased a similare system do the same check and he experienced the same confusion.  I called dell tech support and they said that thier documentation shows the computer to in fact contain ddr sdram.  I'm not sure if i should just accept this as truth or if there is anouther way to check my hardware, I would hate to have paid for ddr sdram and only recieve sdram.  The web program is afterall a DELL program and that is telling me i have sdram only.  If anyone has a possible solution for me it would be greatly appriciated or if others are expieriencing the same issue let me know.  Thanks for any replys.