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The power of two

With single core processors handicapped by design constraints, manufacturers are turning to dual core technology to boost performance levels, says Srikanth R P

For decades, designers have tried to increase the speed and performance of processors by putting an increasingly large number of transistors on to a microprocessor. However, this race for speed has not translated directly into performance. Greater clock speed does not necessarily equate with better performance. What is worse is the fact that higher the speed of a chip, the greater its power consumption and the amount of heat generated. This can cause a processor to seize up. Processor performance depends upon factors such as time to access data in memory, the mechanism used to interconnect the processor, memory and external I/O interfaces as well as power management and heat dissipation.

To overcome this problem, vendors are advocating a new approach—their goal is to put an additional core on the same chip. A dual core processor is essentially two processor cores residing on a single die that translates to double the performance from a single chip. It can also be described as an integrated circuit to which two processors have been attached to reduce power consumption and improve the simultaneous processing of several tasks. While a dual core processor has two cores, it shares some components such as the memory controller.

Says Shrikant Patil, director (Solutions), South Asia, Intel, “Performance improvements have typically been achieved by increasing the clock frequency and cache. One could also improve the whole platform—the chipset and various I/O interfaces. Another way is to increase the number of cores. First, the processor characteristics improve, then the platform gets enhanced and now the cores are increasing.”

Each core may contain separate instruction sets, logical processing units and levels of cache depending upon the processor architecture. There may be a cache for each core or cache memory may be shared by both cores. Sun Microsystems follows the approach wherein two processors share the memory controller but have separate caches, one for each core. IBM’s Power4 or 5 dual core processors have a shared distributed L2 cache with three separate cache banks providing multiple paths to the processor cores. While IBM and Sun Microsystems have already started shipping dual core processors for their Unix systems, AMD has announced an x86 dual core processor and demonstrated a HP ProLiant DL585 server powered by four dual core Opterons.

The need for dual core or multi-core processors has come about on account of new applications that demand greater processing power. At the same time, performance hasn’t kept pace with clock speed. Explains Anil Valluri, Sun Microsystems, “Even though processor manufacturers kept pace with Moore’s law, the speeds did not translate directly into performance. Hence, even if the clock speeds doubled, it translated to an increase of say, 20 or 30 percent, in performance. This has prompted processor manufacturers to look at dual core or multi-core processors which promise greater performance at lower costs.” Sun has a dual core offering in the UltraSparc IV. This processor combines two UltraSparc III cores on to a single die of silicon. As the processor is socket-compatible with its predecessor the UltraSparc III, Sun has doubled the number of CPUs that can be squeezed into a single machine. Sun is also looking at introducing multi-core processors—Niagara (a four core processor with four threads per core) and Rock (an eight core processor with four threads per core).

For the processor vendor, making a dual core processor is a less expensive way to manufacture a new product that promises enhanced performance. As the manufacturing cost is expected to be roughly the same as that of making a single core processor, manufacturers can provide double the performance without charging double the price.

To take advantage of the benefits offered by a dual core processor, software must be aware that a second processor core exists. If the software is symmetric multiprocessing aware (SMP), it can utilise two processors simultaneously. Enterprise software that run on multi-processor servers (2-way and better) can execute multiple threads and make use of SMP architectures. Sanjeev Keskar, country manager, AMD Far East (India) says, “Most software vendors such as Oracle, Microsoft and SAP have dual core applications.” So, re-engineering isn’t going to be required for popular enterprise applications. Typically server applications are processor hungry. “The only way to match the performance demands of such applications is to add more physical cores to a system. Applications requiring huge amounts of processing power such as databases, ERP, CRM or CAD/CAM can benefit significantly from dual core systems,” adds Keskar.

Most vendors have capabilities that allow dual core processors to be placed in existing systems with a processor swap and a BIOS upgrade.

Looking at the boost that dual or multi-core processors can offer, all the vendors have multi-core in their roadmaps. Companies working upon multi-core chips include AMD, Intel, ARM and VIA. ARM has developed a dual core design for cell phones. There is even a 96 core chip from a company called ClearSpeed that is aimed at the supercomputing market. With the future pointing towards dual or multi-core processors, the likes of Intel are planning to incorporate them in desktops and notebooks as well.

srikanth@expresscomputeronline.com