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Topic: Memory management unit


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  U.S. Patent: 5293597 - Concurrent context memory management unit - March 8, 1994
The memory management unit set forth in claim 1 wherein said memory management unit is interposed between a central processing unit (CPU) and said memory and wherein said storage or retrieval instructions are received from said CPU, and wherein said plurality of sources includes a plurality of processes operating within said CPU.
The memory management unit set forth in claim 1 wherein in a default mode said selecting means includes means for selecting a particular one of said stored sets of translation information as a function of the source of said received instruction but independent of whether it is a read instruction or a write instruction.
MMU 40 then consults the virtual address table located in memory 42 for the current process (whose ID was loaded into MMU 40 earlier by CPU 41) and determines the translation and permission access for this virtual address.
www.everypatent.com /comp/pat5293597.html   (2939 words)

  
 Memory management unit - Wikipedia, the free encyclopedia
MMU, short for memory management unit, is a class of computer hardware components responsible for handling memory accesses requested by the CPU.
A key benefit of an MMU is memory protection: an operating system can use it to protect against errant programs, by disallowing access to memory that a particular program should not have access to.
In early designs memory management was performed by a separate integrated circuit such as the MC 68851 used with the Motorola 68020 CPU in the Macintosh II or the Z8015 used with the Zilog Z80 family of processors.
en.wikipedia.org /wiki/Memory_management_unit   (1924 words)

  
 Method and apparatus for a memory management unit supporting multiple page sizes - Patent 5465337
A memory management unit of a virtual address system as claimed in claim 1 in which the pointer to a number of entries having the same assumed virtual page number for entries in which the virtual page number is greater than an assumed length points to an entry in a table in memory.
As with a typical memory management unit, the memory management unit 30 is presented the virtual address sought and compares the upper bits of that address with the upper bits of virtual addresses which are stored in the translation lookaside buffer 31.
This causes the memory management unit 30 to use the circuitry 36 to generate a physical address which is the concatenation of the physical page number, the previously masked least significant portion of the variable page field, and the bits of the small offset field.
www.freepatentsonline.com /5465337.html   (6040 words)

  
 The Memory Management Glossary: M
Operating system memory management is concerned with using the memory management hardware to manage the resources of the storage hierarchy and allocating them to the various activities running on a computer.
OS memory management is also concerned with memory protection and security, which help to maintain the integrity of the operating system against accidental damage or deliberate attack.
A memory manager (often a garbage collector) is said to be moving if allocated objects can move during their lifetimes.
www.memorymanagement.org /glossary/m.html   (2453 words)

  
 Memory Management
Memory management is a general term that covers all the various techniques by which an address generated by a CPU is translated into the actual address of the data in memory.
In a system with memory management the 3-bit word address from the CPU goes directly to the memory, but the 2-bit page address is sent to the memory management unit (see figure 4).
The function of the MMU is to map the addresses generated by the CPU onto the actual memory and to keep track of where data is stored as new tasks are created and old ones removed.
www-scm.tees.ac.uk /users/a.clements/MMU/MMU.htm   (2924 words)

  
 Memory management unit - Patent 4939636
The identification portion ID is the portion which designates the memory management unit MMU which is to receive the communication, and designates by its uppermost bit whether the communication is a global communication directed to all the memory management units or a local communication directed to an individual memory management unit.
However, when communication is through the memory management units and the memory management unit receives the data having the same content as the data it has transmitted, it does not transmit the data to the memory management unit of the next stage.
Since the communication between the memory management units is made by the serial communication system which puts priority on reception, the common memory management information can be made always to coincide with one another between the memory management units without increasing the number of pins of LSI and read-out of wrong data can be prevented.
www.freepatentsonline.com /4939636.html   (6222 words)

  
 MEMORY MANAGEMENT
An address generated by the CPU is commonly referred to as a logical address, whereas an address seen by the memory unit (that is, the one loaded into the memory address register of the memory) is commonly referred to as physical address.
Because it is desirable, in general, that there be several user processes residing in memory at the same time, we need to consider the problem of how to allocate available memory to the various processes that are in the input queue waiting to be brought into memory.
Memory is allocated to the processes until, finally, the memory requirements of the next process cannot be satisfied; no available block of memory (hole) is large enough to hold that process.
emhain.wit.ie /~boneill/webpg.htm   (5689 words)

  
 MMU : Memory management unit   (Site not responding. Last check: 2007-10-18)
MMU, short for Memory Management Unit, is a hardware component responsible for handling memory access requested by the CPU.
Among the functions of this device are the translation of virtual addresses to physical addresses, memory protection, cache control and bus arbitration.
MMU is also an acronym meaning Manned Maneuvering Unit.
www.termsdefined.net /me/memory-management-unit.html   (213 words)

  
 Memory management - Wikipedia, the free encyclopedia
Virtual memory systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the effectively available amount of RAM using disk swapping.
This is generally implemented at the programming language level and is in opposition to manual memory management, the explicit allocation and deallocation of computer memory resources.
In addition to standard memory management, the architectural 640 KB barrier of MS-DOS and compatible systems led to the development of programs known as memory managers when PC main memories started to be routinely larger than 640KB in the late 1980s.
en.wikipedia.org /wiki/Memory_management   (259 words)

  
 MMU: Memory Management Unit   (Site not responding. Last check: 2007-10-18)
Memory Management Unit (MMU) is the hardware component that manages virtual memory systems.
Typically, the MMU is part of the CPU, though in some designs it is a separate chip.
All requests for data are sent to the MMU, which determines whether the data is in RAM or needs to be fetched from the mass storage device.
www.javvin.com /hardware/MMU.html   (126 words)

  
 Feature: High Memory In The Linux Kernel   (Site not responding. Last check: 2007-10-18)
Understanding how basic memory management works, we are better able to define the problem, and finally to review the various solutions.
The virtual address is passed to the MMU (Memory Management Unit of the processor) which converts it to the proper physical address based on the tables set up by the kernel.
Memory in the ZONE_NORMAL region is mapped by the kernel in the upper region of the linear address space.
kerneltrap.org /node/2450/7217   (1335 words)

  
 Memory management   (Site not responding. Last check: 2007-10-18)
When a page fault occurs, the processor's memory management unit (MMU) signals the kernel through an exception and asks it to handle the fault: this can either result in a resolved page fault or in an error.
The MMU causes two page faults and the vnode's getpages method is called for each of them, which then reads the pages from the corresponding file, puts them into main memory and returns control to the caller.
Similarly, pages can be modified in memory after they have been brought to it; at some point, these changes will need to be flushed to the backing store, which happens with the backing object's putpages operation.
www.netbsd.org /Documentation/internals/en/chap-memory.xml   (737 words)

  
 Operating Systems : Memory Management
Virtual memory strategies allow a process to use the CPU when only part of its address space is loaded in the primary.
In virtual memory systems, the size of the virtual address space is greater than the size of the physical address space allocated to the process; that is, the process uses more virtual than physical addreses.
Usually this is done by a hardware unit called the MMU (which sits between the CPU and the cache).
www.bridgeport.edu /sed/projects/cs503/Spring_2001/kode/os/memory.htm   (1848 words)

  
 Z180 Memory Management
The problem of memory management is easy to define: we need some way of connecting lots of memory to a processor that just cannot handle or address it.
If the logical address is 1000, then the MMU allocates this to the bank area (CBAR=F0; 1000 is less than the start of common 1 at F000), and adds the physical base of bank to it (0), giving a translated address of 01000.
In other words, if memory at physical address 20000 is to be displayed, then some routine has to figure out settings for all three MMU registers, plus a logical address, that the 64180 can use to access the memory.
www.ganssle.com /articles/ammu.htm   (4800 words)

  
 A TRANSPARENT TRANSLATION METHOD AND APPARATUS FOR USE IN A MEMORY MANAGEMENT UNIT (WO8802148A1)
In general, upon initiation of system operation, the MMU is in a non-translation mode so that each logical address is provided as the respective physical address without translation.
After the operating system has initialized all appropriate logical-to-physical address translation information in the MMU or in memory, as the case may be, the MMU can be put into the normal translation mode.
Thereafter, the MMU will translate all logical addresses output by the processor to the respective physical addresses according to the translation information established by the operating system.
www.delphion.com /details?pn=WO08802148A1   (763 words)

  
 Memory Management
Virtual memory is a sleight-of-hardware that makes a computer appear to have more physical memory than it does.
These tables also manage critical bookkeeping functions such as determining whether a page is associated with a physical memory page and, if so, when it was last accessed.
The MMU typically uses demand paging to implement virtual memory; that is, it only swings into action when an application demands a resource (perhaps a function call to a shared library, or a spreadsheet reading in more numbers) that isn't in physical memory.
www.computerworld.com /printthis/2001/0,4814,60855,00.html   (802 words)

  
 Memory Management Unit from FOLDOC   (Site not responding. Last check: 2007-10-18)
A PTE may also include information about whether the page has been written to, when it was last used (for a least recently used replacement algorithm), what kind of processes (user mode, supervisor mode) may read and write it, and whether it should be cached.
It is possible that no physical memory (RAM) has been allocated to a given virtual page, in which case the MMU will signal a "page fault" to the CPU.
Some memory management architectures allow each process to have its own area or configuration of the page table, with a mechanism to switch between different mappings on a process switch.
www.instantweb.com /foldoc/foldoc.cgi?MMU   (481 words)

  
 CS 537 - Memory Management   (Site not responding. Last check: 2007-10-18)
Whenever the CPU wants to access memory (whether it is to load an instruction or load or store data), it sends the desired memory address to the MMU, which translates it to another address before passing it on the the memory unit.
The MMU allows a contiguous region of virtual memory to be mapped to page frames scattered around physical memory making life much easier for the OS when allocating memory.
Since in modern computers, the speed of memory is often the bottleneck (processors are getting so fast that they spend much of their time waiting for memory), virtual memory could make programs run twice as slowly as they would without it.
www.cs.wisc.edu /~solomon/cs537/paging.html   (6308 words)

  
 MMU - Memory Management Unit
Memory Management Unit, translates virtual to physical addresses and provides access permission control.
Astronauts on board a NASA space shuttle can strap on this large rocket backpack and maneuver during a spacewalk (officially known as an Extra Vehicular Activity) instead of remaining tethered to the shuttle or to the Canadarm.
(memory management unit) (n.) In hardware, memory address mapping.
www.auditmypc.com /acronym/MMU.asp   (171 words)

  
 [No title]
Since all modules are sharing the same address space, the memory manager must maintain proper permissions for each segment used by a module, and it must enforce these permissions when interactions with main memory are required.
Usability: Programs should be able to have the kernel communicate with the MMU on their behalf for all memory management issues.
Virtual Address Structure A virtual address to a byte in memory is identified as follows: The upper 8 bits consist of the segment identifier (used to index segmentTable and modeMatrix), and the lower 24 bits specify the offset.
web.mit.edu /~noto/Public/6.033/proj1.1.doc   (1215 words)

  
 The Memory Architecture and the Cache and Memory Management Unit for the Fairchild CLIPPER Processor | EECS at UC ...
The Fairchild CLIPPER is a new high-performance three chip module consisting of a microprocessor chip and two cache and memory management (CAMMU) chips, mounted on a small PC board.
The CLIPPER memory architecture is a separate 32 bit logical address space for each of the user and supervisor, with facilities for transferring information from one to the other.
Virtual memory support is provided by a memory management unit on each CAMMU, each of which includes a translator that maps 32-bit virtual addresses through a two level page table to 4096 byte pages, and a 2-way set associative with 16-byte lines and with LRU replacement within each set.
www.eecs.berkeley.edu /Pubs/TechRpts/1986/5193.html   (384 words)

  
 Ruud's Commodore Site: 74LS612 - Memory Management Unit
With the MMU the ROM is enabled at $8000 and does not affect the new Kernal in RAM.
The reason is very simple: once you have placed the MMU out of the picture, you won't be able to change the configuration anymore and you are stuck with the momentary one for "the rest of your life".
If you place it before the MMU it always will be accessible but the disadvantage is that it can get in the way when there is a need to remap certain areas to the area the MMU occupies.
www.baltissen.org /htm/74ls612.htm   (2439 words)

  
 Paged Memory Management
To convert the virtual address into a physical address, the memory management unit looks up the page index in the page table, takes the resulting physical address, and adds the offset to get the final physical address.
Because pages of physical memory must be 4KB-aligned, the bottom 12 bits of the address are treated as zero and those bits are made available for other purposes.
This saves some memory and indirection that would be required for the page table itself, at the cost of allocation granularity - it also saves TLB entries.
channel9.msdn.com /ShowPost.aspx?PostID=117507   (1299 words)

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