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  • Organization &amp; Architecture UNISA Studies &ndash; Chap 4

    - by MarkPearl
    Learning Outcomes Explain the characteristics of memory systems Describe the memory hierarchy Discuss cache memory principles Discuss issues relevant to cache design Describe the cache organization of the Pentium Computer Memory Systems There are key characteristics of memory… Location – internal or external Capacity – expressed in terms of bytes Unit of Transfer – the number of bits read out of or written into memory at a time Access Method – sequential, direct, random or associative From a users perspective the two most important characteristics of memory are… Capacity Performance – access time, memory cycle time, transfer rate The trade off for memory happens along three axis… Faster access time, greater cost per bit Greater capacity, smaller cost per bit Greater capacity, slower access time This leads to people using a tiered approach in their use of memory   As one goes down the hierarchy, the following occurs… Decreasing cost per bit Increasing capacity Increasing access time Decreasing frequency of access of the memory by the processor The use of two levels of memory to reduce average access time works in principle, but only if conditions 1 to 4 apply. A variety of technologies exist that allow us to accomplish this. Thus it is possible to organize data across the hierarchy such that the percentage of accesses to each successively lower level is substantially less than that of the level above. A portion of main memory can be used as a buffer to hold data temporarily that is to be read out to disk. This is sometimes referred to as a disk cache and improves performance in two ways… Disk writes are clustered. Instead of many small transfers of data, we have a few large transfers of data. This improves disk performance and minimizes processor involvement. Some data designed for write-out may be referenced by a program before the next dump to disk. In that case the data is retrieved rapidly from the software cache rather than slowly from disk. Cache Memory Principles Cache memory is substantially faster than main memory. A caching system works as follows.. When a processor attempts to read a word of memory, a check is made to see if this in in cache memory… If it is, the data is supplied, If it is not in the cache, a block of main memory, consisting of a fixed number of words is loaded to the cache. Because of the phenomenon of locality of references, when a block of data is fetched into the cache, it is likely that there will be future references to that same memory location or to other words in the block. Elements of Cache Design While there are a large number of cache implementations, there are a few basic design elements that serve to classify and differentiate cache architectures… Cache Addresses Cache Size Mapping Function Replacement Algorithm Write Policy Line Size Number of Caches Cache Addresses Almost all non-embedded processors support virtual memory. Virtual memory in essence allows a program to address memory from a logical point of view without needing to worry about the amount of physical memory available. When virtual addresses are used the designer may choose to place the cache between the MMU (memory management unit) and the processor or between the MMU and main memory. The disadvantage of virtual memory is that most virtual memory systems supply each application with the same virtual memory address space (each application sees virtual memory starting at memory address 0), which means the cache memory must be completely flushed with each application context switch or extra bits must be added to each line of the cache to identify which virtual address space the address refers to. Cache Size We would like the size of the cache to be small enough so that the overall average cost per bit is close to that of main memory alone and large enough so that the overall average access time is close to that of the cache alone. Also, larger caches are slightly slower than smaller ones. Mapping Function Because there are fewer cache lines than main memory blocks, an algorithm is needed for mapping main memory blocks into cache lines. The choice of mapping function dictates how the cache is organized. Three techniques can be used… Direct – simplest technique, maps each block of main memory into only one possible cache line Associative – Each main memory block to be loaded into any line of the cache Set Associative – exhibits the strengths of both the direct and associative approaches while reducing their disadvantages For detailed explanations of each approach – read the text book (page 148 – 154) Replacement Algorithm For associative and set associating mapping a replacement algorithm is needed to determine which of the existing blocks in the cache must be replaced by a new block. There are four common approaches… LRU (Least recently used) FIFO (First in first out) LFU (Least frequently used) Random selection Write Policy When a block resident in the cache is to be replaced, there are two cases to consider If no writes to that block have happened in the cache – discard it If a write has occurred, a process needs to be initiated where the changes in the cache are propagated back to the main memory. There are several approaches to achieve this including… Write Through – all writes to the cache are done to the main memory as well at the point of the change Write Back – when a block is replaced, all dirty bits are written back to main memory The problem is complicated when we have multiple caches, there are techniques to accommodate for this but I have not summarized them. Line Size When a block of data is retrieved and placed in the cache, not only the desired word but also some number of adjacent words are retrieved. As the block size increases from very small to larger sizes, the hit ratio will at first increase because of the principle of locality, which states that the data in the vicinity of a referenced word are likely to be referenced in the near future. As the block size increases, more useful data are brought into cache. The hit ratio will begin to decrease as the block becomes even bigger and the probability of using the newly fetched information becomes less than the probability of using the newly fetched information that has to be replaced. Two specific effects come into play… Larger blocks reduce the number of blocks that fit into a cache. Because each block fetch overwrites older cache contents, a small number of blocks results in data being overwritten shortly after they are fetched. As a block becomes larger, each additional word is farther from the requested word and therefore less likely to be needed in the near future. The relationship between block size and hit ratio is complex, and no set approach is judged to be the best in all circumstances.   Pentium 4 and ARM cache organizations The processor core consists of four major components: Fetch/decode unit – fetches program instruction in order from the L2 cache, decodes these into a series of micro-operations, and stores the results in the L2 instruction cache Out-of-order execution logic – Schedules execution of the micro-operations subject to data dependencies and resource availability – thus micro-operations may be scheduled for execution in a different order than they were fetched from the instruction stream. As time permits, this unit schedules speculative execution of micro-operations that may be required in the future Execution units – These units execute micro-operations, fetching the required data from the L1 data cache and temporarily storing results in registers Memory subsystem – This unit includes the L2 and L3 caches and the system bus, which is used to access main memory when the L1 and L2 caches have a cache miss and to access the system I/O resources

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  • Winning With Long Tail Keywords - Become an Authority in Your Niche

    Most accomplished webmasters and SEO experts will mirror my words here. Winning in the long tail is essential to becoming an authority in your niche. Too often do webmasters go for the "frontal assault" when trying to win a niche, which more often than not results in their competition finding out about them, then pushing them out of the game with their strong list of long tail rankings. So, what can you do in order to dominate your niche and become an authority?

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  • PowerPivot: Putting two stocks on the same PivotChart

    - by AlbertoFerrari
    In a previous post , I have used a stock exchange scenario to speak about how to compute moving averages in a complex scenario. Playing with the same scenario, I felt the need to compare two stocks on the same chart, choosing the stock names with a slicer. As always, a picture is worth a thousand words, the final result I want to achieve is something like this, where I am comparing Microsoft over Apple during the last 10 years. It is clear that I am not going to comment in any way why traders seem...(read more)

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  • Steve Ballmer on Cloud Computing &ndash; We&rsquo;re all in

    - by Eric Nelson
    Steve spoke last week (March 4th 2010) on the possibilities of the Cloud and the importance to Microsoft. Of our 40,000 people building software, 70% of the people at Microsoft today are working on the Cloud – 90% in a years time In other words: The video is 85mins of Steve and there is an easy way of navigating to some soundbytes on presspass. I also like the new website that simplifies our story and commitment around the cloud http://www.microsoft.com/cloud/ Which includes an easy mapping between well known product offerings from Microsoft and the Cloud “equivalents”

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  • Kompozer gives an error when runned under 12.10 amd64

    - by blade19899
    I downloaded kompozer extracted it and run kompozer like ./kompozer So then I get this error in the gnome-terminal Gtk-Message: Failed to load module "overlay-scrollbar" /usr/lib/gtk-2.0/2.10.0/menuproxies/libappmenu.so: wrong ELF-class: ELFCLASS64 (kompozer-bin:8651): Gtk-WARNING **: Failed to load type module: /usr/lib/gtk-2.0/2.10.0/menuproxies/libappmenu.so How can i get Kompozer to work under 12.10 amd64? note: The error above had some dutch words in them so i translated it!

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  • Why does ubuntu 11.10 freeze when playing video?

    - by psylockeer
    I run ubuntu 11.10 on i5 CPU with 4GB RAM nvdia geforce GTS 250 connected to widescreen tv (HDMI) When using vlc, xbmc or boxee to play movies the system randomly freeze, the audio is looping the last words of the video file and nothing is responding. So I have to manually reset the system. Can anybody help? P.S. I forgot to mention the the log file was full of line regarding xbox 360 wireless receiver (I dual boot with windwos 7) so I unplugged it to see if that counts

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  • The Science of Creating a Money Making Keyword List

    Creating a money making keyword list is the foundation of your website marketing strategy. If your keyword list contains the right words or phrases then you will see plenty of traffic finding your site. If the keywords are not specific enough or are too general then your traffic will suffer and those that do happen to find your site may just look around a second or two and then move on.

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  • The Science of Creating a Money Making Keyword List

    Creating a money making keyword list is the foundation of your website marketing strategy. If your keyword list contains the right words or phrases then you will see plenty of traffic finding your site. If the keywords are not specific enough or are too general then your traffic will suffer and those that do happen to find your site may just look around a second or two and then move on.

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  • What Are Google Supplemental Results?

    Google supplemental Results are Web pages partly Google-indexed and are hard to find in the normal search engine result page (SERP). In other words supplemental results are the URLs that reside in Go... [Author: John Anthony - Computers and Internet - June 10, 2010]

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  • What does 'Nightly Builds' mean?

    - by dbramhall
    I have been using open source projects for a while and been developing upon the open source applications and every so often I come across the words 'Nightly Build' and I have always been curious as to what it actually means. Does it literally mean the projects are done purely as side projects (usually at night after everyone has finished their day jobs) and there's no true contributor/dedicated development team or is it more complex than that?

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  • Tips to Find the Best Keyword Research Software

    Keyword research plays a critical role in search engine optimization. The search engines use some keyword phrases to identify the web pages that are relevant to those words. For instance, if you are selling soft toys, then soft baby toys, buy soft toys, soft play toys are some of the right keywords that can bring good number of traffic to your site.

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  • Making a clone of Starcraft legal?

    - by user782220
    My question is similar to a previous question. Consider the following clone of Starcraft: Change the artwork, sound, music, change the names of units. However, leave the unit hit points unchanged, unit damage unchanged, unit movement speed unchanged, change ability names but not ability effects. Is that considered illegal? In other words, is copying the unit hit points, damage, etc. considered illegal even if everything else is changed?

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  • PowerPivot: Putting two stocks on the same PivotChart

    - by AlbertoFerrari
    In a previous post , I have used a stock exchange scenario to speak about how to compute moving averages in a complex scenario. Playing with the same scenario, I felt the need to compare two stocks on the same chart, choosing the stock names with a slicer. As always, a picture is worth a thousand words, the final result I want to achieve is something like this, where I am comparing Microsoft over Apple during the last 10 years. It is clear that I am not going to comment in any way why traders seem...(read more)

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  • Linux is not an operating system, or is it?

    <b>Technology & Life Integration:</b> "There is a word in the English language (which I hope I am using) called context. In other words, I use the word Linux in the context of a complete Linux based distribution and believe that my readers understand that context."

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  • Write SEO Articles For Humans, Not Machines

    We would like other people to be able to find our web pages and read our writing or see our images. In other words, we need to be present in web search results. SEO is an important factor to reach high positions in search results but you should always create pages for humans and only optimize them for search engines.

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  • Making a clone of a game legal?

    - by user782220
    My question is similar to a previous question. Consider the following clone of starcraft. Change the artwork, sound, music, change the names of units. However, leave the unit hitpoints unchanged, unit damage unchanged, unit movement speed unchanged, change ability names but not ability effects. Is that considered illegal? In other words is copying the unit hp, dmg, etc. considered illegal even if everything else is changed.

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  • 2 Day Training on Windows Azure

    - by Sahil Malik
    SharePoint 2010 Training: more information Will Azure make you loose your job? Well if you don’t jump onboard and get on with the times, yes it will. (My words, not Microsoft’s).I will be delivering a 2 day training on Windows Azure. Complete with hands-on labs, lots of good learning. When – November 17nth, 2011Where – Oslo, NorwayMore Information | Register Now. Details - Read full article ....

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  • Setting Up an Ecommerce Website

    Ecommerce is actually electronic commerce which is done online. In other words, setting up an ecommerce is like setting up a virtual store where people can shop and purchase some items.

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  • What is your toolset?

    - by MrG
    What tools, free or otherwise do you use to help you with your "webmastering" I'm thinking along the lines of, Link checking, analytics, web stats, page validation, plus anything else you can think of! Personally I use: webmasters tools, google analytics, AWstats I'm looking for anything (free or paid) which maybe hovering under my radar which could be of use. (edit - missed a couple of words out of first line!)

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  • Does one's choice of 3d modeling software used during asset creation affect performance at runtime?

    - by user134143
    Does software used to create 3d assets (for game development specifically) have an impact on the efficiency of the program? In other words, is it possible to reduce the operating footprint of an application merely by utilizing alternative development software during production of 3d assets? If you use two different applications to create a 3-dimensional image of a box, can one of them result in better performance if aspects of the image are identical? I am attempting to get the information I need without causing unnecessary debate over specific software choice.

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  • Website Design and Ethical SEO

    There are a host of website design and SEO companies in Chicago. SEO consists of services of consultation, tailor made changes to the owner's website, analysis of keywords and market research, website hosting on high speed servers, on page and off page SEO, email marketing, a matching blog, using Webmaster 2.0, Google analytics setup that distinguishes which of the client's ads are most effective and disposes of the rest thus cutting expenses, and SEM (Search Engine Marketing) like pay per click management and usage of Google Ad words is all a part of website design in Chicago.

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  • SEO Copywriting - Worth the Money

    If you have thought of paying for the SEO copywriting services long back, then you might have also thought about writing the promotional copy by yourself. The things that are included in SEO copywriting is just words and sentences that are arranged into proper paragraphs. You will be thinking why do you need to waste money on SEO copywriting?

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  • How do I make a rich menu for an appindicator?

    - by Erigami
    I'm adding menu items to an appindicator in pygtk. I don't want them to behave like ordinary menu items: I want them to have normal appearance, but not to respond to mouse hovers and mouse clicks. The way I imagine the new sound menu will behave. In other words, I want to prevent the MenuItem selection that's going on below: How do I go about doing that? What events should I swallow, or is there a better way?

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  • Looking for terminology for the relation of a subject and a predicate

    - by kostja
    While writing some predicates for collection filtering I have stumbled over the choice of the right words for the relation of the subject and the predicate (English is a foreign language for me). What I ended up writing was "Subjects matching this predicate..." This seems to be incorrect, since predicates are functions and not regular expressions. But saying "Subjects for which this predicate returns true..." sounds awkward to me as well.. So what would be the correct term?

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