If we have 2 GiB RAM and a processor Pentium 4 with 3.2 GHz and 2 MiB Cache , What will you use ,windows 7 32 bit or 64 bit , and why ?

You use Windows7 (32bit)

The terms 32-bit and 64-bit refer to the way a computer's processor (also called a CPU), handles information. The64-bit version of Windows handles large amounts of random access memory (RAM) more effectively than a32-bit system.

To install a64-bit version of Windows 7, you need a CPU that's capable of running a64-bit version of Windows. The benefits of using a64-bit operating system are most apparent when you have a large amount of random access memory (RAM) installed on your computer, typically4 GB of RAM or more. In such cases, because a64-bit operating system can handle large amounts of memory more efficiently than a32-bit operating system, a64-bit system can be more responsive when running several programs at the same time and switching between them frequently.

Most programs designed for the32-bit version of Windows will work on the64-bit version of Windows. Notable exceptions are many antivirus programs.

A 64-bit version of Windows7 is good but as you don't have sufficient RAM (at least 4GB) and if  you rely on devices that don't have supporting64-bit drivers then 32-bit Windows7 might be the better choice.

As long as support for64 bit OS on pentium4, if you have P4  Socket LGA 775 then you can install it, if its Socket 478 then its not supported.

A processor having32 bit address bus can address upto "2 to the power32" blocks which means it can address4 Giga numbers of addressable memory blocks. Size of a memory block is1 Byte. So, the maximum addressable memory size is4 GigaByte. All the pentium series (p1 - p4) processors are single core processor. It means the address bus is32 bit. So, you cannot use more than4GB memory in this processor type.

A32 bit Operating System (OS) can operate all the single and multi-core processors. But, a64 bit OS must be installed in multicore (at least2 cores) processors.

So, you have no option to use a64 bit OS. You must use Windows732bit in your case.

32-bit is recommended because your ram is2 GB and32-bit processor can hold ram till4 GB

For the specs you provided I would suggest you install windows732-bit 

Because64-bit windows requires you to have more than2GB of ram as well as a processor capable of handling64-bit operating systems.

Also read the following : 

• I have got a similar spec. computer running windows732-Bit just fine but not that fast though.

• windows XP32-bit will run perfectly on your system and it would be fast too on a Pentium4 with3.2GHz processor but i don't recommend it because it is prone to alot of viruses and malware these days.

• I suggest you try out LINUX  lt is completely free and its blazingly fast + free of viruses so you would not have to install an antivirus. It will work very fast on your PC I have tried tested and used it on one of my PCs with2GBs of RAM, P43.2GHz . You can also try it out from a USB without having to install it.

Linux comes in may different user interfaces and they call them different distros. Following are some I recommend you to try. 

• Linux Mint  (www.linuxmint.com/)

• Zorin-OS    (zorin-os.com/)

• fedora        (fedoraproject.org/)

• korora        (https://kororaproject.org/discover) 

you also did not tell us about the details or model of the processor so we could tell if your processor supports64-bit Windows or not.

For your PC specifications I suggest you do not install windows64-bit even if you add another2GBs of ram totalling to4GBs of ram.

I will use Windows732bit, because for64bit you need4Gb ram

To install a64-bit version of Windows 7, you need a CPU that's capable of running a64-bit version of  Windows, so you have to install32 bit Win7 on above mention senerio/

I prefer to use the32bit in terms of processing your system cosums only a minimal usage or cashe memory. besides if you compare the two bits the32 and64 it doesnt matter at all. the important for this is the sytem safe usage..because ocationaly sometimes problem occur to your system if you use a higher bit OS wih lower cashe memory.

I agreed with Mr. Saqib Mehmood . For Windown64Bit you must have4GB ram. 

It's advisable you install32 bit, if you install64 bit it will be heavy on that particular machine . For64 bit OS . the mamory should be4 Gb and above