![]() The data structures that map linear to physical addresses are called page tables they are stored in main memory and must be properly initialized by the kernel before enabling the paging unit. If the memory access is not valid, it generates a Page Fault exception (see Chapter 4 and Chapter 8). One key task in the unit is to check the requested access type against the access rights of the linear address. The paging unit translates linear addresses into physical ones. 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. A page frame is a constituent of main memory, and hence it is a storage area. The paging unit thinks of all physical RAM as partitioned into fixed-length page frames. A page refers both to the set of linear addresses that it contains as well as to the data contained in this group of addresses. ![]() ![]() Access rights and physical address mapping in the kernel is done at a page level rather than for every linear address. However congtiguous pages can be present anywhere on the physical RAM. Contiguous linear addresses within a page are mapped onto contiguous physical addresses on the RAM chip. Memory in Linux is organized in the form of pages (typically 4 KB in size).
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