Operating Systems Important Definitions
Single contiguous allocation: Simplest allocation method used by MS-DOS.
All memory (except some reserved for OS) is available to
a process.
Partitioned allocation: Memory is divided in different blocks
Paged memory management: Memory is divided in fixed sized units called
page frames, used in virtual memory environment.
Segmented memory management: Memory is divided in different segments (a
segment is logical grouping of process' data or code)
In this management, allocated memory does'nt have to
be contiguous.
Most of the operating systems (for example Windows and Linux) use Segmentation with Paging.
A process is divided in segments and individual segments have pages.
Paging is a memory management scheme that eliminates the need for contiguous allocation of physical memory. This scheme permits the physical address space of a process to be non – contiguous.
Virtual Memory is a storage allocation scheme in which secondary memory can be addressed as though it were part of main memory.
The mapping from virtual to physical address is done by the memory management unit (MMU) which is a hardware device and this mapping is known as paging technique.
The Physical Address Space is conceptually divided into a number of fixed-size blocks, called frames.
The Logical address Space is also splitted into fixed-size blocks, called pages.
A Memory Management technique in which memory is divided into variable sized chunks which can be allocated to processes. Each chunk is called a Segment. A table stores the information about all such segments and is called Segment Table.
Page Fault – A page fault is a type of interrupt, raised by the hardware when a running program accesses a memory page that is mapped into the virtual address space, but not loaded in physical memory.