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Developing new, high-end CPUs is a '''very''' expensive proposition. Both the logical complexity (needing very large logic design and logic verification teams and simulation farms with perhaps thousands of computers) and the high operating frequencies (needing large circuit design teams and access to the state-of-the-art fabrication process) account for the high cost of design for this type of chip. The design cost of a high-end CPU will be on the order of US $100 million. Since the design of such high-end chips nominally take about five years to complete, to stay competitive a company has to fund at least two of these large design teams to release products at the rate of 2.5 years per product generation. Only the personal computer mass market (with production rates in the hundreds of millions, producing billions of dollars in revenue) can support such economics. As of 2004, only four companies are actively designing and fabricating state of the art general purpose computing CPU chips: [[Intel]], [[AMD]], [[IBM]] and [[Fujitsu]]. [[Motorola]] has spun off its semiconductor division as [[Freescale]] as that division was dragging down profit margins for the rest of the company. [[Texas Instruments]], [[TSMC]] and [[Toshiba]] are a few examples of a companies doing manufacturing for another company's CPU chip design.
== Embedded design ==
The majority of computer systems in use today are embedded in other machinery, such as telephones, clocks, appliances, vehicles, and infrastructure. An [[embedded system]] usually has minimal requirements for memory and program length and may require simple but unusual input/output systems. For example, most embedded systems lack keyboards, screens, disks, printers, or other recognizable I/O devices of a personal computer. They may control electric motors, relays or voltages, and reed switches, variable resistors or other electronic devices. Often, the only I/O device readable by a human is a single light-emitting diode, and severe cost or power constraints can even eliminate that.
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The cache controller knows where in main memory any piece of data came from. It therefore "knows" that different data in the cache are actually from different programs entirely, a side effect of modern [[computer multitasking|multitasking]] [[operating system]]s. In simultaneous multithreading designs, the cache controller will not look just for the instruction that is ready, but the program (or thread) that is "most ready". This can be quite effective in many cases, as programs often switch between handling data and processing, simultaneous multithreading can make more effecient use of the various units in these cases by going out and finding entirely different programs to run while the "running one" waits for data.
== See also ==
* [[Microprocessor]]
* [[Moore's Law]]
* [[Amdahl's law]]
* [[Simultaneous multithreading]]
* [[RISC]]
* [[CISC]]
[[Category:Computer architecture]]
[[Category:Computer hardware]]
[[nl:Processorarchitectuur]]
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