is it true that single ram perform good.......?

there are 2 advantages of 1 stick over 2 1. as abv said you get empty socket for next upgrade 2. well 1 stick has all memory blocks joint... so if a program is using many contiguous blocks... the 1 gb stick would provide it easily!! plus 1gb stick is some 40$ for DDR1 here and 512 is 32$ so even i would say go for 1 gb!!

I think your friend is trying to stop your PC from performing better. Where did he get the idea that 2 RAMs are slower than a single RAM? Try to ask him how many RAMs his computer has?. The idea of RAM is to store cache files (temporary memory) for so that the processor can process it faster without going to far into the hard disk to find out. So the processor can easily fetch the temporary stored files from the RAMs. However RAMs actually work almost like Hard disk if the space getting larger. Which means it is going to be harder for the processor to find where the files are because it is so large that making it difficult to find. So in order to get a larger RAMs i mean more RAMs like you are trying to do. You must have a Pentium that is capable of processing that bigger space RAMs. Otherwise it would be wasted for you because the RAMs will not fully utilized to its full capacity. Therefore you need to match your processor speed and the amount of RAMs space that suit the speed in order for them both fully performing at the highest level.

Sometimes 2 sticks of ram are good if you want performance. But if you need more RAM because your PC is already running slower than usual when a number of applications are open, single or double sticks would be fine. It's the total amount which matters of that's the case. However, if you want real speed, you can use 2 sticks and interleave them. 2 512MB sticks will still be at 512MB but your PC will use both sticks to store and retrieve data faster as it alternates between the 2. Much like how RAID hard drives work. I'm not sure if there is still some today. I haven't seen a lot of people use RAM this way. Maybe because RAMs today are much faster.

It depends on you if you want to have two 512MB ram then they will have to have the same clock speed to run properly.However if your computer has more than two ram slots it would be better to max out your computers ram,The max ram that windows xp recoginzies is 3GB and the max windows vista and windows 7 Regonize is 16GB.I would recommand you max out your systems ram