How fast a computer runs isn't simply a matter of the speed of the main processor, known as the central processing unit. While chip manufacturers stake their advertising claims on the records their chips set in speed tests, the interplay of the various computer components such as graphics cards and motherboards is every bit as important.
One significant role is played by the individual data connections within a PC -- the so-called bus. The most important of these connections is the front side bus (FSB). It is connected not only to the CPU but also to the memory (RAM) and graphics cards as well.
The speed of the bus is expressed in units called megahertz. The FSB can be critically important for a little concern, depending upon the application at hand.
"For computation-intensive programs with little demand on the drive, processor speed is everything," says Christian Anderka, of chip giant Intel. "If there needs to be communication with memory, however, the overall speed is highly dependent on the bus speed."
"The speed at which data travels along the front side bus can vary, depending upon the processor," explains Chistof Windeck, editor of German-based computer magazine c't. And that speed can also be affected by the rate at which the memory chips (RAM) in the computer run. Fast memory chips of the type known as "synchronous dynamic random access memory" (SDRAM) can be accessed at a maximum speed of 133MHz.
Other types of memory, such as "double data rate" (DDR-DRAM), can transfer information at a speed of two data units per cycle, meaning that speeds of up to 266MHz can be achieved.
But speed barriers, even in today's fast computers, are already an issue. The good news is that there's no dearth of ideas on how to speed up data exchange within PCs.
Pentium4 chips, for example, have a front-side bus of 400MHz, which is a substantial improvement over bus speed of previous Intel processors. But the 400MHz FSB is somewhat misleading. "The Pentium4 chip actually runs the bus at no more than 100MHz," says Anderka.
"But through Intel's so-called Quad Pump Technology, four data units can be sent simultaneously per cycle."
"In current systems, RAM is a bottleneck," says computer scientist Rainer Spallek from the Technical University of Dresden. "Memory chips process information at a speed significantly slower than the central processing unit's speed," Spallek says.
To make matters worse, neither the current connection structures within a PC nor the available storage modules can reach speeds of a gigahertz, due to physical limitations. "This gap between the quicker CPU and the slower memory will not disappear with future systems and will probably always represent a bottleneck," Spallek adds.
The ports between the processor, memory, and graphic cards represent another bottleneck in most PCs, says Spallek. With many PCs sold today, the graphics card is still linked to through the peripheral component interconnect (PCI) bus to the motherboard. As popular as PCI connections are, the PCI bus long ago out live to its usefulness. It can only reach speeds of 33 to 66 MHz.
More modern motherboards rely on an accelerated graphics port (AGP) to connect the graphics card to the computer's CPU. "Intel intended its AGP slot as a way for the graphics processor to draw upon the resources of the CPU," Windeck said.
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