# How a 32 bit number stored in 64 bit processor with 32 bit OS? [duplicate]

When a 64 bit OS runs on a 64 bit processor, the processor processes the whole 64 bit (8 bytes) in one go. Suppose a 32 bit OS runs on a 64 bit processor, how is data extracted? Is 32 bits (4bytes) extracted or whole 64 (8 bytes)? Is that 32 bit (4byte) data stored like 32 bits storage wastage and 32 bits as data ? Like (32bit(zeroes) + 32 bit (data)) for 64 bit processor 32 bit OS?

• Hint: "the processor processes the whole 64 bit (8 bytes) in one go" - not true, depends on CPU instructions. – Biswapriyo May 29 at 10:29
• Just because you can only represent up to 2³² in a 32-bit register does not mean that you can only use data up to that size. There are mathematical methods for adding numbers far larger than you can work with in a given block size, and there are some registers (even within a 32-bit processor) that are 128 or 256 bit that are used for vector mathematics. "32-bit" just refers to the address register size. – Mokubai May 29 at 10:51
• We have a lot of old questions on this type of thing which might be worth searching through: superuser.com/search?q=64+32+bit – Mokubai May 29 at 10:53