I encountered 2 terms ,"FAT32", a file system and "Windows Vista 32 bit".

I found that the meaning of a 32 bit OS is that that the OS deals with data in chunks of minimum size 32 bits. I don't quite understand the depth of that, but I figure ,every file in that system with that OS should have a minimum size of 32 bits. I also read that these 32 bits are used to hold data of files' location(reference) and details. Which of it is it?

I have also read that 4 GB of RAM is all that is needed at the most if you're on a 32 bit OS. But I don't understand why.

If there are 32 bits to hold info about files and their locations,there can be 2^32 possible combinations of it. But I have found in many places,2^32 is divided by 1024 thrice to get 4GB. Why? Did that 2^32 become equal to 2^32 bytes?

And about filesystems I read a similar explanation for what 32 means in FAT32. It is supposed to mean that 32 bits are used to number file system block. Now how is different from the number before the OS?


There is a difference between data in memory and data on disk. Also, it is not true that a 32bit OS devides data in 32 bit chunks per say. It is just an OS that can make use of optimizations in 32bit processors, which are indeed optimized for 32 bit arithmetics, so therefor it may be faster to use 32 bit values that larger or even smaller values.

A 32 bit number can contain values between -2billion and +2billion, or between 0 and 4 billion (2^32-1), depending if it is signed or not. This limitation is what you find in all these 32 bit systems. A 32 bit OS can use at most 2^32 bytes of data (4GB), which is why it is pointless to have more memory in a PC with such an OS. FAT32 cannot hold files larger than 4GB. A FAT32 disk is devided in chunks, but the larger the disk, the larger those chunks, since a disk can be devided in at most 2^32 chunks. This means that on a very large disk, these chunks become so large that lots of disk space is wasted, because no two files may share a single chunk.

The limitations of the file system are not directly related to that of the OS. If you format a disk as FAT32, it still has the limitations of the FAT32 system, regardless of the OS used. Otherwise, a 32bit OS may very well be capable of using a file system that allows largers disks and files larger than 4 GB.

  • 1
    I wouldn't quite say pointless, physical address extension (PAE) and all.
    – Tim Post
    Jun 3 '12 at 15:44
  • Where are the addresses to all the bytes of memory(RAM) (byte-addressable) stored?
    – learner
    Jun 3 '12 at 17:55
  • What do you mean? They don't all get stored? Your PC has a continues plock of bytes of RAM. The OS assigns blocks of that to a process (on request), and the process can address each byte in it. The OS only needs to remember the position and size of each block. Otherwise, it would need 4 bytes per byte of memory to store the location of that byte. Wouldn't be that efficient. :)
    – GolezTrol
    Jun 3 '12 at 19:26
  • @TimPost. You're very right about that, although I didn't want to make it even more complex. ;) OP was talking about Windows, and although Windows 32bit does support PAE, it still won't use the space above 4GB. But it is possible indeed, especially in Linux and OSX.
    – GolezTrol
    Jun 4 '12 at 9:59

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