Does Samsung's touchwiz show up in your manager app? if it doesn't, the extra RAM is being used up by touchwiz and your android system processes.

In general, android RAM should always be close to full. it is intelligent enough to keep commonly used apps and processes in RAM so that they can launch quicker, making your phone faster.

 

Yes it was, do you see anything like android system in your RAM usage?

 

That is likely the culprit. Please do keep in mind though that Android RAM is doing it's job correctly when the RAM i almost full: this is allows the phone to keep commonly used programs in cache and launch them faster.

 

so its normal for an Android device to consume so much ram even in idle state?

 

Yes, completely normal.

It's Unix-style memory management (Linux and Mac OSX are the same), rather than Windows-like.

 

Imagine you buy a 100 room hotel and only ever let out 20 rooms. You've just wasted a large chunk of cash (nearly a pun there ;-)) on rooms which go unused.

Similarly, unused RAM is wasted RAM. You paid for it. Why not use it? Android will load the things you do use and also pre-load (cache) things you haven't used yet, but might. It will also retain programs you have used, but no longer are using, in the anticipation that you will use them again (soon). In this way your phone is prepared ahead of times for things you are likely to want to do, which should in theory speed things up overall.

This is why apps like automatic task killers are usually so utterly futile. They are in a constant battle with the operating system to undo each other's work.

If you have an unhealthy obsession with free RAM then purge the cached apps if you like, but over time the OS will reload them. If/when it runs out of RAM for something that needs doing then the OS will purge enough cached apps for yout to free the space required.