Two identical machines (P4 and the usual items). These were same make/model/firmware/etc right down to the clone of the hard disk and OS.
We ran a DVD final cut program (it makes the production copy) on both machines. One machine had 512M, then other 1G.
The machine with 512M finished in 6 hours. The one with 1G RAM finished 5 minutes sooner.
To make sure this test was fair, we swapped RAM with each box and repeated the runs. Again, the 1G machine won by 5 minutes over the 6 hour run.
As such, my response is this. Since you are writing about a P4 class machine and not any 64-bit CPU, you will get as much usage out of this 1G RAM as you possibly can for as many years as it lasts and may never add more RAM.
My thought? Go with the cheaper option.
Bob
1 GB DDR-SDRAM (DDR2-400, 1 GBx1)
1 GB DDR-SDRAM (DDR2-400, 512 MBx2)
^two choices I'm interested in for a sony S-380 series notebook
-I was configuring a notebook. What is the difference between these two and why does one cost more...should I spend the extra money? Is it worth it?
Thanks, any help would be appreciated...

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