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If i had 160 GB of hard drive on a 32 bit OS what is the largest possible memory address? and if a 32 bit pointer can map upto 4 GB of memory how is it possible to map an address above 4 GB?

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There is no direct mapping between memory address space and location on the HDD.

The instructions to the OS on where to find the data it needs is more Country->City->Street->Building than Latitude+Longitude

Read more here: Wikipedia on file systems

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It all depends on your file system. Memory is addressed by bytes, which causes a 4GB limit (2^32). File systems are typically addressed by clusters which are larger than 1 bytes. If you used a 4KB cluster you could access 4096 * 2^32, or roughly 4TB of hard drive space. You still only access 2^32 elements but each would be 4KB in size, resulting in a total much larger than 4GB.

But the 2^32 limit can show up in other places - file systems such as NTFS can access a maximum of 4,294,967,295 files on a volume.

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