In trendy methods, applications usually have addresses that entry the theoretical most memory of the computer architecture, 32 or 64 bits. The MMU maps the addresses from each program into separate areas in physical memory, which is generally much smaller than the theoretical most. This is possible because programs rarely use giant quantities of memory at any one time. Most modern operating programs (OS) work in concert with an MMU to provide digital memory (VM) assist. The MMU tracks memory use in fastened-dimension blocks often known as pages. If a program refers to a location in a page that isn't in bodily memory, the MMU sends an interrupt to the working system. The OS selects a lesser-used block in memory, writes it to backing storage equivalent to a tough drive if it has been modified because it was read in, reads the page from backing storage into that block, and units up the MMU to map the block to the initially requested page so this system can use it.
This is called demand paging. Some simpler actual-time operating systems don't help digital memory and don't want an MMU, but nonetheless want a hardware memory safety unit. MMUs usually present memory protection to dam makes an attempt by a program to entry memory it has not beforehand requested, which prevents a misbehaving program from using up all memory or malicious code from reading knowledge from one other program. Zilog Z8000 household of processors. Later microprocessors (such because the Motorola 68030 and the Zilog Z280) positioned the MMU together with the CPU on the same built-in circuit, as did the Intel 80286 and Memory Wave later x86 microprocessors. Some early techniques, especially 8-bit systems, used quite simple MMUs to perform bank switching. Early techniques used base and bounds addressing that additional developed into segmentation, or used a fixed set of blocks instead of loading them on demand. The distinction between these two approaches is the scale of the contiguous block of memory