[SOLVED] Why Dsp's operating at MHz range ,where as the general processors work GHz?

Why the DSP Clock frequency is still at Mhz and General purpose processor at GHz range ....

Recently, integrated circuit (IC) designers have started taking advantage of high-density, high-speed CMOS technology to develop digital signal processing (DSP) intensive clock source solutions that are both high performance and frequency agile. These DSP-based architectures use a low frequency resonator element (typically a quartz crystal) and a high-frequency on-chip VCO to produce a frequency agile high-speed, low-jitter output clock whose output rate is digitally-controlled and whose jitter performance equals that of traditional high-performance VCSOs. The resolution of the digital frequency control can be very fine, much less than one ppm, with a continuous tuning range of more than one GHz. Compared to the high frequency (>100 MHz), high absolute accuracy (<±20 ppm) and pulled (±20-100 ppm) resonators required in traditional high-performance VCSOs, these resonators can be very small and inexpensive because the reference resonator is low frequency (<40 MHz), has loose absolute frequency accuracy requirements (<±10,000 ppm) and is not pulled with changes in DCO output frequency. These resonators can be very small and inexpensive.

The simple answer is the DSP chips don't need to run any faster in many cases.

Nearly all the functions in a DSP chip are one instruction / cycle such as the bog standard MAD instruction as these effectivly get piplined on eafter each other the DSP clock rate helps define the cuttoff frequency of the filter you use.

As often the DSP chip is asked to do little more than a series of Bi-quad filter functions on audio or lower frequencies you just dont need GHz clock DSP's.

However... in fairly recent years people have started at looking into Software Defined Radio this means that the frequencies the DSP chip is filtering is not audio but RF into the UHF range so yes DSP chips will start having GHz clock frequencies.

The assumption isn't completely true. You also find multiple GHz DSP. But because DSP is mostly embedded computing, they also have to be scaled to low power, small form factor designs. Except with handhelp mobile devices, this idea apparently isn't very popular for general computing applications. Everybody wants a GHz Multicore processor to read his E-Mail.