Downsampling vs. ADC with lower Sample-Rate I would like to know in general where the advantages and disadvantages are:

Downsampling of a high sampled continuous analog signal in FPGA or µC and
Direct use of a lower sampling rate, i.e. using an analog to digital converter with a lower sampling rate ?
Are there any differences or does it have the same effect ?
Because almost every DSP-System i see uses a way Oversampling followed by Decimation (Downsampling + AAF-Filter) instead of adequate Sampling Rate without Decimation.

Greetings
With downsampling you have complete control over the process and it comes down to what compromise of processing complexity, delay, aliasing and loss of passband you can accept.
With a lower rate A/D you are pretty much at the mercy of someone elses spectral trade-offs and in addition you get the quantization/noise of one analog pass.
-k