Pages

The address space of even a 32 bit processor is quite large, and if the operating system is to keep track of it all it needs to divide it into more manageable parts.

The operating system divides the address space into pages. Pages can be many different sizes, generally they are around 4KB, but this is not a hard and fast rule and they can be much larger.

The page is the smallest unit of memory that the operating system and hardware can deal with.

Additionally, each page has a number of attributes set by the operating system. Generally, these include read, write and execute permissions for the current page. For example, a page must be marked if it contains executable code.