For the sake of efficiency, linear addresses are grouped in fixed-length intervals called pages;
contiguous linear addresses within a page are mapped into contiguous physical addresses. In
this way, the kernel can specify the physical address and the access rights of a page instead of
those of all the linear addresses included in it. Following the usual convention, we shall use
the term “page” to refer both to a set of linear addresses and to the data contained in this group of addresses.
The paging unit thinks of all RAM as partitioned into fixed-length page frames (they are
sometimes referred to as physical pages). Each page frame contains a page, that is, the length
of a page frame coincides with that of a page. A page frame is a constituent of main memory,
and hence it is a storage area. It is important to distinguish a page from a page frame: the
former is just a block of data, which may be stored in any page frame or on disk.
