At first glance, everything looks very confusing, but it is actually quite simple. At this point, I also want to encourage all developers to take a peek at the compilers and CPUs. I hope I could reasonably explain what the small difference of 32 bit and 64-bit processors is. If you want to use the whole range of 2^64 (64-bit processor) you can simply use “ int64_t”. AMD64 is a 64-bit processor architecture that was developed by Advanced Micro Devices (AMD) to add 64-bit computing capabilities to the x86 architecture. n 64-bit Mode: 64-bit code/data running under a 64-bit OS n. That means with an int of 4 bytes you can “ only” save a number in the range of 2^32 (that is not really 100% correct, because it is possible to set some prefixes like singed or unsigned, but in fact, the range is the same, you can read more here). C compilers had to be selected for various code vs. Pretty simple, it depends on the compiler, because the compiler defines the size. For example 4 Byte on a 32 Bit processor or 8 Byte on 64 Bit processor but, as you can see in this little C example, by default the int has a size of 4 bytes, but why? In fact, the integer should be as big as the default CPU register size. If you read the IEEE-754 you’ll see that there is no default definition of the size of an integer type.

By default, the size of a datatype is defined in IEEE-754, in combination with the language C it is more specified in the ANSI/C standard. (I had used gcc as the compiler by the way).

So, at this point, you might ask yourself why is the basic int type only 4 bytes big on a 64Bit operating system?Īt first, some facts about the C compiler (I’m not sure but I think that other compilers work in the same way). On the left side is the datatype and on the right side is its size in bytes. Hint: If you don´t know, how to compile a C program, click hereĪfter running the program you should see something like that:

64 bit processor vs 32 bit processor