The Virtual Memory Manager (VMM)
The Difference between virtual memory and physical memory
Physical memories are the RAM chips purchased and placed in a slot on the computer motherboard. The RAM is the first memory used when the computer requires memory usage, such as for loading an application or opening a document.
Virtual memory is stored on the hard drive. Virtual memory is used when the RAM is filled. Virtual memory is slower than physical memory, so it can decrease the performance of applications.
Physical memory allocates information in a "first in, last out" process. The information is placed on the stack. Virtual memory uses a process ...view middle of the document...
3) Your computer uses Virtual Memory during normal operation, but if your computer begins to run out of physical memory then your computer will resort to using the virtual memory more often.
Virtual memory also allows the sharing of files and memory by multiple processes, with several benefits:
System libraries can be shared by mapping them into the virtual address space of more than one process.
Processes can also share virtual memory by mapping the same block of memory to more than one process. Process pages can be shared during a fork system call, eliminating the need to copy all of the pages of the original (parent) process.
Users can add more RAM to a computer to increase performance of a computer that uses virtual memory too often. Virtual memory settings can be controlled through the operating system
The benefits of running applications when the operating system uses a virtual memory manager.
Most operating systems use a virtual memory manager (VMM) whose responsibility is to manage the relationship between the virtual organizations of memory as seen by an application with the physical organization of memory from the operating system’s point of view. Virtual memory addresses must be mapped to physical address and vice versa. Write a four to five (4-5) page paper in which you: The memory mapping manager views its local memory as a large cache of the shared virtual memory addresses space for its associated processor (SPECTORA).
How virtual memory addresses get translated into physical addresses step by step.
• Each frame is associated with a register containing
• Residence bit: whether or not the frame is occupied, Occupier: page number of the page occupying frame Protection bits
• Page registers: an example Physical memory size: 16 MB Page size: 4096 bytes Number of frames: 4096
• Space used for page registers (assuming 8 bytes/register): 32
• 18 Kbytes
• Percentage overhead introduced by page registers: 0.2%
• Size of virtual memory: irrelevant
• CPU generates virtual addresses, where is the Physical page?
• Hash the virtual address
• Must deal with conflicts
• TLB caches recent translations, so page lookup can take several steps
• Hash the address
• Check the tag of the entry
• Possibly rehash/traverse list of conflicting entries 19
• TLB is limited in size
• Difficult to make large and accessible in a single cycle.
• They consume a lot of power 27% of on-chip for StrongARM .( TARJAN)
Some physical addresses are decoded to select memory hardware. Physical memory includes ROM as well as RAM. Each block of physical memory has a range of physical addresses. The physical addresses where RAM or ROM can be found depend on the particular computer system (TANG).
Physical memory does not necessarily occupy sequential addresses. There can be (and often are) gaps, ranges of physical addresses that do not relate to either memory or devices, between ROM addresses and RAM addresses....