The following explanation is incorrect considering the architectural design but will help you understand what to expect from a DSP.
It can reproduce an electric/electronic hardware (like a synthesizer, a compressor, a reverb...) from its schema/circuitry (technical design an specifications) consisting i.e of analog or digital oscillators, lfo's, filters, transistors, tubes, lamps, AD/DA converters etc with theoretically no latency and same dynamic range as the original hardware device.
A plugin running on a DSP is like having the hardware without physical user interface but a software GUI instead running on your computer to operate the hardware that is instantiated with it. This means you cannot run native plugins unless coded to run on a DSP as it's instruction set is different from other CPU like the one from Intel, Motorola or Sparc by example.
Of course, it's still about executing mathematical operations with the "little" difference that the instructions are dedicated to digital signal processing only so they run much faster then any other CPU listed above.
You will find here Rapid Development Environments to visually design a circuitry and that will compile a source code using the DSP instruction set, comparable to a Visual C or .Net by example... "reproducing" an hardware.
UAD-2 Apollo and Sattelite use third generation SHARC processors from Analog Devices with performance up to 450 MHz/2700 MFLOPs.
http://www.analog.com/en/products/la...-overview.html
Hope this will help you understand the benefit of using DSP's.