How much RAM for my PC

You  want to buy a  new PC/Lappy OR you already have a PC/Laptop sometimes you may feel like your system is slow and you want to increase its speed. In these cases some people blindly go for any company which they feel is the best. Some think about what configuration to take and then take the company/product which suits their requirement. If you are in the second category then here are few simple calculations which may help you to decide properly. If you are in the first category, then also you can find it helpful to decide which is best fit for you in that "Best" company :-) :-)

1)How many Bit Operating System(32 or 64)
It is the very important question to ask first.
Lets consider the 32 bit operating system(OS).

It can address upto 2^32 bits(^ means power) . i.e 4GB.
And addressing will take some space. So around 3.5GB memory will be usable in a system with 32 bit operating system.

If u didn't get how it is, here is the calculation..
2^10=1024.
2^32=2^10* 2^10* 2^10* 2^2=1024*1024*1024*4.
 we have 1024bit=1Kilo Byte(KB)
1024 kb=1Mega Byte(MB)
1024Mb=1Giga Byte(GB)
so it is 4GB.

For 62 bit OS:
It can support very huge amount of memory. For the time being we  can think it supports whatever we wish to put :-) :-)

Calculation:
2^64= 2^32 * 2^32. i.e u can think as 4GB * 4GB=16* 2^ 18 RAM  ideally !!!

So next time when you hear about any PC(generally workstations and other high end systems) with 200 GB memory or so.. think that OS as 64 bit OS only :-)

2. Why  more RAM ?
RAM  decides how many applications you can open simultaneously. More RAM you have you can open more applications. 

But RAM doesn't decide how quickly your PC opens(only open not finish running) an application. 
mean to say you already have 4GB RAM in your 32 bit system. adding 4 more GB of RAM won't make your system faster. It simply enables you to open some more applications in parallel.

Speed of opening an application and speed of calculations, processing  is decided by the CPU.More the CPU speed, more quickly you can open an application..

But reverse is true. 
i.e if you have shortage of RAM say only 512 MB of RAM in your system, then inspite of having higher speed CPU your system may run slow when you run memory intensive applications.(Applications which require more memory like  Britanica Encyclopedia, Games etc). 
now lets see how much RAM is ideal for your CPU

3. Processor Speed
a) Single Core Processor
Here calculation is simple. If processor speed is 2.6Ghz it can take upto 2 GB of RAM (RAM with 1.3Ghz RPM). 
1.33 * 2= 2.6 is nearly same as 2.6 Ghz of Processor

So if you have 3.2 Ghz Processor(say AMD Turion) you can add upto 2.5 GB RAM

b)Dual Core Processor
Here processor speed is doubled. 
Say you have dual core processor with 2.3 Ghz. As it has 2 cores(2 CPUs) its processing speed is doubled. i.e its processing speed is 4.6Ghz now. 
So you can add around 3.5GB of RAM . 
(RAM with 1.33Ghz RPM. 1.33*3.5 = 4.655)

c)Quad Core or even more
Here processing speed will be speed of one core multiplied by number of cores. 
Here point to note is maximum RAM used is 4GB if OS is 32 bit(as explained Question 1). 
If it is 64 bit OS means no such limits

d)Some Exceptions : Dependency on number of threads of CPU
Earlier it was one thread per CPU. now there are processor with 2 threads per CPU. 
If it is more than one thread per CPU, then that CPU processing speed is doubled. 


4.Whether you have Graphic Card
 If you want to play certain games, then you need to have atleast 1 GB of Graphic card. It acts as a co- processor. Mean to say it acts as a processor dedicated for displaying graphics. So it also takes up RAM. If you have 1GB graphic card of say 1.33Ghz then it will take up around 1GB RAM having 1.33 Ghz speed. So If you have 2GB Graphic card your system can take 2GB more RAM apart from what your processor takes.. 

There are some other concepts like amount of Cache and others. But lets don't complicate ourselves too much for one session and can take it some other time :-) :-)

Getting confused too much ? 
Don't worry . Lets do some simple calculations so that we can revise whatever we discussed so far and familiarize ourselves with these calculations. .

What is the RAM needed in below cases
(Do the calculation and then see the answer at the bottom to verify)
Case 1) Single core Processor with 2.4 Ghz speed. No Graphic card, 32 Bit OS
Case 2) Dual Core processor with 2.33 Ghz speed. 512 MB built in graphic card with 1.33Ghz, 64 bit OS
Case 3) Dual Core Processor with 2.33 Ghz Speed. 2GB external Graphic card with 1.33 Ghz, 32 bit OS
Case 4) Quad Core Processor with 2.4 Ghz speed. 2 threads per core. 2 GB external Graphic card with 1.33 Ghz, 64 bit OS
Case 5)Dual core Processor with 2.4Ghz. 1 GB Graphic card(with 1.33 GHz) , 32 Bit OS. Have put 4GB RAM with 1.33 RPM.  How much RAM is usable (usable to OS)

Note: Graphic card calculation hold the same irrespective of whether they are internal(embedded) or external ..

Answers: 
1) upto 2 GB of RAM 
2) upto 4 GB.  (3.5 without 512 MB Graphic card)
3) upto 5.5 GB  ( as 2 GB will be taken by Graphics card. Remaining 3.5 GB for 4.66Ghz processing speed. As 1.33 * 3.5 = 4.65)
4)Quad core. So 2.4* 4= 9.6. But 2 threads per CPU. so It is 19.2 Ghz.+ 2.6 by graphic card(2*1.33)
so in Total 21.8 around 22.
So we can add upto 16.5 GB RAM !!! (This is 64 bit OS not 32 Bit OS )
5) Around 2.7 GB usable !!
1GB RAM is taken by graphics card.
We saw in question 1, in 32 bit OS, maximum of 3.5 GB is usable(rest taken by addressing).
So around 2.7 GB will be usable by OS.

Ok guys, with this we are ending this session.
Hope this info and calculations are Useful J J