大牛或专业人士评评这个。 我个人认为随着CPU速度已经满足普通需要,RISC这种容易为特殊任务优化的架构比 CISC更有优势。 http://www.tgdaily.com/hardware-features/65123-on-arm-versus-x8 Posted August 2, 2012 - 05:52 by Guy Wright It seems like everyone in the industry wants to compare ARM (and other variants of RISC processors) to x86 (and other variants of CISC processors). For example, analysts ask, can Intel muscle it’s way into the mobile market? Can ARM sneak in the back door of the tablet, laptop, or even desktop markets? Who is faster, more powerful, cheaper, uses less power, less space, and generates less heat? These are not easy questions to answer and the major players spread misinformation by the shovel full. So let’s take a step back and look at what makes each technology tick. RISC (reduced instruction set computing) technology has been around since before the acronym was even invented. It goes back as early as the 1960s (it could be argued that the CDC 6600, one of the first supercomputers designed by Seymour Cray in 1964, was a RISC machine). The term ‘reduced instruction set’ is a bit misleading since modern RISC processors can have just as many instructions as CISC (complex instruction set computing) processors. The primary difference is that in a RISC processor all instructions are formatted exactly the same way and all take exactly the same time to execute – usually one cycle per instruction. To achieve this consistent, compact design many instructions and addressing modes that were built into CISC processors – such as floating point operations and division – were not included in RISC processors. These operations were usually offloaded to coprocessors. This approach meant that instructions could be executed very, very quickly and the chip architecture could be simplified. RISC processors tend to have far fewer transistors than CISC processors - as few as half the number in many cases. And fewer transistors means less power, less heat, and a smaller footprint, features that make them ideal for small devices with limited power. Also, because the architecture is simplified and performance is so predictable compilers can be optimized to eke out every possible iota of performance. Of course, RISC processors have grown progressively more complex over the years and as each licensee adds their own twists to the original architecture the stack of developer manuals gets taller and taller. The main reason that game consoles (which use RISC processors) perform so well is that there are no surprises. Developers know exactly what the hardware is capable of and can optimize their games to use every ounce of power. They don’t have to worry about different screen resolutions or vagaries in graphics cards or unpredictable performance hits if the user has multiple applications running – the environment is always the same. You could also argue that the performance of all-things Apple is also a result of carefully controlled, very predictable hardware and software environments – develop for a Mac or an iPad or an iPhone and you know exactly what you are getting into. To use an Olympic games metaphor, the RISC architecture is like an Olympic pool. It’s exactly fifty meters long. Not forty-five meters or fifty-two- and-a-half meters or whatever the pool just happens to be. It’s very specific, and since it’s so specific swimmers can hone their technique to fit the pool. They know, with a good amount of certainty, exactly how many strokes it will take them to get to the other side, turn, and head back. Toss those same swimmers in the ocean and tell them to race out to that piece of driftwood and back and you might have different winners standing on the podium. Yes, there are some downsides to RISC processors. For one, as I mentioned earlier, certain tasks (like floating point operations or division) can’t be performed with a single instruction except in some of the newer RISC designs. So even if a single instruction runs faster on a RISC processor than the same instruction on a CISC processor, it may take dozens of instructions to perform some operations that a CISC processor can do with a single instruction. And there is a double-edged-sword with RISC technology. The companies that develop the designs don’t actually manufacture the chips – they license the technology (referred to as cores – reusable, and sometimes customizable , blocks of logic or chip layout designs) to other corporations. And like any good department store would do, they lower the licensing fees on older versions of the design. So if a manufacturer wants to use the latest and greatest version of a RISC design, they pay a premium, but if they don’t need the latest and greatest features for a particular application they can license an older version. Nearly every RISC architecture design ever developed is still available if you want it. Now for some manufacturers this is a good thing. If you need a chip to run a waffle maker you probably don’t need the newest RISC cores – you can probably get away with an older design. But it also means if you’re developing a chip for a new smart phone and just want to save a few bucks you can license a design that’s a few revs older than the newest design. ( Granted, you can also buy older versions of CISC chips too, but companies like Intel don’t manufacture 286 or 386 chips anymore). Also, companies that license cores can modify them to suit their specific needs, so, for example while the Nvidia Tegra Kai processor slated to power the Microsoft Surface tablet may be based on the ARM Cortex, Nvidia has already stated that the Tegra line comes in a variety of configurations with and without certain features. The CISC architecture, as the name implies, has a richer and more complicated set of instructions built into the main processor. This complexity sometimes comes at the expense of performance but it can also provide more muscle when performing certain tasks. It also makes it easier to program complicated tasks (although achieving high levels of optimization can be more problematic). The CISC architecture approach began in the days when RAM was expensive (and comparatively slow by today’s standards) and programming was done at very low levels (programs were written in assembly code rather than higher-level interpreted or compiled languages). The more functionality built into the main processor the easier it was to program and, in most cases, it was faster than moving data back and forth from memory (or even worse hard disk- based ‘virtual memory’). A divide command might take a handful of clock cycles to complete but it was damned easier than building a divide sequence of instructions when all you had was add, subtract, multiply, and compare. One disadvantage of the CISC approach was that designers had to account for a lot of different possibilities, and that meant sometimes there was functionality built-in that wasn’t actually used. It might take the same number of clock cycles to perform a simple operation as it did to perform a complex operation. It also meant that it was harder to predict performance because different instructions would take a different amount of time to complete. Another disadvantage is that all this functionality comes with a cost – the more functionality you build into the processor the more transistors you need and more transistors require more power and that means more heat, higher costs, and sometimes a larger size chip. (You can get around the size problem by making the circuitry smaller but that raises the cost. You can reduce the number of transistors but that means less functionality. You can get around the power problem by running the chip at a slower speed but that makes it, well, slower). Of course, there are two non-hardware specific advantages to CISC. First, Intel is a mega-giant in the chip design and manufacturing business with lots of money and some very big guns so they can devote enormous resources to customizing the x86 line – resources than most RISC developers can only dream about. Second, there are roughly a zillion applications tailored to run on x86 processors. Now that second advantage doesn’t hold true in the mobile space where there are roughly a zillion apps tailored to run on Android and iOS. Granted, a high percentage of those mobile apps could be considered trivial (not a lot of acoustics modeling, 3D rendering, or CAD apps written for smart phones... yet). So which processors are better? Depends on what you are trying to do. If you ’re building a mobile device and don’t care about some of the more advanced features (or can live with stripped down versions of them) then RISC is a good choice. If, on the other hand, you want to do some serious hard-core processor-intensive tasks then CISC processors are the way to go. Try as they might (and they’ve been trying for years) Intel just can’t quite get the hang of developing embedded processors. And while they have tried (and failed) on various occasions, RISC processors just can’t seem to crack the desktop market. Maybe that will change in the coming years as the lines continue to blur but it probably won’t happen overnight. And a quick historical footnote: Ironically, Intel first developed the 8080 – forerunner of the x86 line – back in 1974 as a low-power, reduced function processor for calculators. ARM processors, on the other hand, began life in 1985 when Acorn Computers released a new chip based on the MOS Technology 6502 processor and called it, logically enough, the ARM-1 (Acorn RISC Machine). Read more at http://www.tgdaily.com/hardware-features/65123-on-arm-versus-x86-part-ii#Lr7jXcAic4QeAfLy.99 Read more at http://www.tgdaily.com/hardware-features/65119-on-arm-versus-x86#RJi1MqDVU9Sil1xO.99
c*a
3 楼
正在准备装订,请给为致电以下。 我想给每页supporting docuemtns 都打印一次统一页码,然后在最前面给个精确到页的index. 但这样搞很费时,并且很步灵活(一旦打印,不能调整材料),还有我还有一个考虑就是在reference letters 上做页码,涉嫌篡改reference letter !? 多谢!!
p*r
4 楼
I didn't go through the entire article. It's just too long. I guess I pretty much know what's going on. I witnessed Intel using its manufacturing and large volume advantage to kill RISC one after another(I am old enough). However, this time. it's different. * ARM has much bigger ecosystem in the mobile space than all RISC processors used in the workstation/servers before. Now its ecosystem is even bigger than x86 in PC in terms of volume if you count all mobile phones, tablets, and even some of the media players. * Many companies making ARM chips can survive with low margin. That's very different than all the companies were making RISC processors before, such as IBM, Sun, DEC and HP, and MIPS. Can Intel this time kill all ARM with its advantage on the manufacturing ? I don't think so. Yes, Intel has 1-2 years ahead in terms of manufacturing process, but cost of manufacturing is not low. Here are the key factors that Intel killed all RISC processors before. * 1.5x or more in the performance. * Same power consumption * Same price range or lower. In order to kill ARM. x86 processors still have to do the same. This time I seriously doubt because Intel can achieve the last one(price). Intel has been selling ultra low power mobile CPU for at least $150. Can Intel sell it for $30-$50 ?
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【在 r******y 的大作中提到】 : 大牛或专业人士评评这个。 : 我个人认为随着CPU速度已经满足普通需要,RISC这种容易为特殊任务优化的架构比 : CISC更有优势。 : http://www.tgdaily.com/hardware-features/65123-on-arm-versus-x8 : Posted August 2, 2012 - 05:52 by Guy Wright : It seems like everyone in the industry wants to compare ARM (and other : variants of RISC processors) to x86 (and other variants of CISC processors). : For example, analysts ask, can Intel muscle it’s way into the mobile : market? Can ARM sneak in the back door of the tablet, laptop, or even : desktop markets? Who is faster, more powerful, cheaper, uses less power,
I used the relative page numbers (added to the right bottom corner of PDF files using Acrobat Pro). For example, for Exhibit A.1 that contains 5 pages and Exhibit A.2.1 4 pages, you have something like: Exhibit A.1 1/5 Exhibit A.1 2/5 ... Exhibit A.1 5/5 Exhibit A.2.1 1/4 Exhibit A.2.1 2/4 .. Exhibit A.2.1 4/4 So when you change something, you only need to update the page numbers relevent to that Exhibit; no overall index page is needed then. My package ended up with only 8 tabs, which are Cover Letter, Petition Letter, Exhibit List, Exhibits A, B, C, D, and E. I numbered pages the same way for all supporiting docs, including the reference letters. It didn't seem to cause any trouble, at least for my case.
页的index. 就是在reference letters 上做页码,涉嫌篡改reference letter !?