Recent Advances in Microprocessor Design
Christian Manfred Wimmer, S0501100, Student Computing & IT, Year3
Abstract —This paper will give an overview of the recent advances in microprocessor design. It will cover 64bit processors, specially designed mobile CPUs, and multi-core technologies along with Hyper-Threading Technology. Finally, as glance on things to come, hardware support for Virtualization will be covered.
Index Terms —Microprocessors, Virtual computers, Parallel processing
LOT has happened since the first transistor based CPUs where sold in the late 70s. This paper will give an overview of the recent advances in microprocessor design.
II. 64BIT PROCESSORS AND THE MASS-MARKET
In 2003 a new revolution started, that is, when you listen to the marketing department of AMD and alike. In fact 2003 marks the introduction of 64Bit CPUs to the mass market. 64Bit wasn’t that new as it sounded because MIPS, Sparc and Alpha CPUs where already available for a few years and with the Playstation 2 this type of CPU already found its way into our living rooms.
So what is all the fuss about, you might ask? The answer is quite simple – it’s all about RAM and the addresses needed to organize it. A normal PC can handle up to 4 GB of RAM without a problem but a look at the inside shows that Windows XP for example takes around half of that memory for itself, leaving only 2 GB for the applications. In case you ever worked with large databases or love to render 3D pictures you probably know that this kind of applications can never have enough memory and 2 GB virtual address space suddenly seems to be relatively tiny. 
Normally Intel is the company who pushes new innovations forward, but in this case AMD was the one to introduce 64Bit to the consumer market. In the middle of 2004 Intel realized, it has to do something in order to keep up with the success of AMD and it was decided that the technology AMD64 will be used in new Intel CPUs. A lincence trade agreement allowed Intel to do this without paying royalties to AMD. Intel called it
Manuscript handed in March 19, 2006.
Christian Manfred Wimmer is a student at the North East Wales Institute of High Education, dept. School of Computing & Communications Technolody and is aiming for a BSc (hons) Computing & Information Technology degree EMT64 and started to offer products for workstations and small servers. 
Due to the lack of applications and operating systems that support 64bit, the technology hasn’t quite kicked off yet. Luckily AMD64/EMT64 is an extension to the 32bit software model and therefore 32bit software is running on this CPU without major speed losses. Probably the biggest problem of the 64bit technology is the driver support. The 64bit operating systems require new 64bit drivers and as drivers for many operating systems, including the famous Windows, are closed source. Unless there is a generic driver old hardware may become redundant and it might take a while until a wide variety of 64bit drivers will be available.
In the Wintel world the upcoming Windows Vista will play an important part in the future of 64bit CPUs as it will be available in 64bit and will come with a many 64bit drivers.
The 64bit technology turns out to be far less effective as the marketing departments want us to believe. Unless the applications you run use a ton of memory, and not a lot of them do, 64bit is more or less useless at the moment for the average user. However chances are high that a 64bit CPU will be in the next PC you buy, and as it runs 32bit software without speed losses there is no harm done.
III. GOING MOBILE
A. Need for mobile CPUs
The power consumption of Desktop CPUs is rising constantly. The heat that is produced is also a problem and the cooling systems needed to keep the CPUs from melting also drain a lot of power. Electric energy however is the one thing that is always short when it comes to mobile computing. No one is willing to carry his Laptop or PDA around with a car battery. Therefore power saving is a major issue in mobile computing. Mobile CPUs can be divided into two classes. 
B. Mobile variants of Desktop CPUs
Mobile variants usually work just like their Desktop siblings. These CPUs have been carefully selected by the manufacturers for low power consumption. One a single silicon wafer hundreds of CPU cores are created and some of those are able to reach high clock speeds at relatively low supply voltage.
To reduce the requirement for power even further mobile CPUs also get taught a few tricks, however special motherboards (like in Laptops) are needed for this.
Normal office software like MS Office usually doesn’t use a lot of CPU power and therefore the CPU is idling most of the time and this circumstance is used for power saving. Basically the CPU shuts down all non essential resources and consumes less power this way. Nowadays this kind of CPUs also sleeps in between keystrokes of even the fastest writer.
This kind of CPUs is often easily distinguished from normal desktop CPUs by a little ‘mobile’ in the name like Intel’s Mobile Pentium.
C. Specially designed power saving CPUs
Special CPU architectures promise even more energy efficiency. The following architectures have been designed with the requirements for mobile computing in mind.
1) Intel Centrino
The most well known brand in this sector is probably Intel’s Centrino Architecture. The designers of this architecture took a close look at the Pentium architecture and tweaked it for power saving as much as they could, without sacrificing too much performance in the process .
The Pentium-M only uses about 6 Watt in battery-operation and under full-load while it’s Desktop sibling, the Pentium IV, uses above 24 Watt. A Pentium-M clocked at 1.5 GHZ should have the same performance as a 2 GHZ Pentium 4, not bad when you keep in mind that it uses less than a quarter of the power. 
A different approach is used by the company Transmeta with their Cruseo, or the newer version Efficeon, design. They are using a technology known as ‘ Code Morphing ’.
Transmeta CPUs can be seen as somewhat incomplete, the Code morphing engine emulates all the missing functions. This special software is loaded right after the start of the system from a special BIOS-like chip on the main board. Therefore the CPU can be ‘updated’ to learn new instructions and bugs can be fixed (Pentium bug), this works pretty much like a BIOS update.
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Fig. 1. The Code Morphing software mediates between x86 software and the Crusoe processor .
LongRun power management is basically controlled by the Code Morphing, allows the processor to adjust its clock frequency and voltage on the fly. Because power varies linearly with clock speed and by the square of the voltage, adjusting both can produce cubic reductions in power consumption whereas conventional CPUs can adjust power only linearly. A conventional CPU, throttling back the processor speed by 10% cuts power by 10%, whereas under the same conditions, LongRun power management can reduce power by almost 30%. Although this technology help to save a lot of power Transmeta hasn’t had very much success with it in the past few years.
3) ARM – small and powerful
ARM, whose Headquarter is based in Cambridge, United Kingdom, is the industry's leading provider of 32-bit embedded RISC microprocessors with almost 75% of the market (2002). ARM is a “fabless” company – they only sell ‚ “intellectual property‘ such as Core designs. Licensees include big names like Intel, IBM, Motorola, Samsung… pretty much everyone in the semiconductor market! 
Jazelle is a technology that allows ARM CPUs that implement it, to run Java bytecode natively. This technology is often used by mobile phone manufacturers to speed up execution of Java games and apps, which is probably what drove development of the technology.
Thumb allows the 32bit ARM RISC processors to partly operate in 16bit mode to, simplified, save a little Memory.
This has been introduced at a later stage of the development on demand by the manufacturers. This is out of the ordinary as ARM has therefore gone 32bit -> 16bbt, and not the other way round like Desktop CPUs.
Our modern life demands flexibility and mobility. Notebooks are replacing normal Desktop PCs more and more and the recent boom in mobile MP3 players like the iPod has created an enormous market for mobile CPUs. This trend will surely not stop overnight and therefore specially designed CPUs for this market have a bright future, along with the manufacturers that manage to stay on top of the technology curve.
IV. MULTI CORE AND PARALLEL PROGRAMMING
Everyone wants more CPU performance, but not necessarily pay more for it. However the cost for speeding up CPUs is increasing exponentially. In the last couple of years it has turned out that with today’s production techniques in CPU fabs 4 GHZ is the highest clock rate that can be achieved in a cost effective way. The solution for this problem is quite simple: Put more CPUs onto one chip. But before we take a closer look on multi-core chips let’s review one of the technologies from the “pre-multi” area namely Simultaneous Multi Threading or, like Intel likes to call their implementation, Hyper-Threading Technology.