hey guys , I am a second year  electronics engineering student ...... wanted to know which one of a digital gyro or analog gyro is better .... A digital gyro works on spi and i2c interface ..(which is quite difficult to understand )... and a analog gyro simply gives analog output voltage which can simply be used with micro controller..... so which one is reliable?? also wanted to know about programming aspects... 

Well it's common sense. Analogue is old technology, just like analogue watches. Digital is more precise and less prone to weather conditions.

Rahul,
Since you're doing your engineering, this rule of thumb will always come in handy. Precision and Accuracy are two aspects of measurement and control, and will always have a compromise. Read this up http://en.wikipedia.org/wiki/Accuracy_and_precision

Analogs are accurate but less precise and digitals while precise are less accurate. Same goes for thermometers, watches, and every other digital thing. While working with digital stuff values a "real" value is always clamped to the closest "step" value in the digital range. A simple example would be if one has a 2 bit range, the number of unique states would be 4 (0-3). Now how does one represent 2.5. Clearly there is no way, so 2.5 will either be snapped to 2 or to 3. This is called the resolution and the ADC is responsible for this so if your board has a 10 bit ADC, you know there are 1024 such states of measurement.

As far as SPI and I2C are concerned, both can be mastered easily if you're good at basics of micro controller programming and debugging. Start with something simpler like UART communications and graduate to SPI/I2C.

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in the Digital World of aeroplanes, backup to Digital displays (Aircraft flying parameters) are analog dials, picked up from independent sources. Rate display of analog is smooth and reliable, digital display of rate of change for reasons mentioned by Girish is still jerky.

Bottom line is digital and analog, both has its place and use. may or may not be complimentary to each other. Ask music connoisseurs, they will prefer songs over LP (Given all its scratches and glitches) than any MP3 or digital sound, LP is really, Real  

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