op-amp: what is internal frequency compensation?
Frequency compensation of a multi-stage amplifier is frequently necessary to prevent oscillation when feedback is applied. Op-amps are often intenaly compensated for unity gain (worst-case) by inserting a dominant pole at a low frequency such as 10Hz. Sometimes they are compensated for a minimum gain that is higher than 1, 5 or 10, for example, which allows better performance, provided you always need a gain that is that high. The size of capacitor required (maybe low double-digit pF) can be made on the IC with little trouble. 

Uncompensated amplifiers have an external RC network or two that can be optimized for the situation. They used to be quite common (eg. LM709) but are relatively rare these days. 

Here is the internal circuitry of the LM324 (one amplifier, simplified) showing the compensation capacitor Cc. 



And the LM709, showing the external input and output compensation networks for unity gain. 



As you can see, there are no capacitors on the chip: 



More mathematics here. Google op-amp frequency compensation for much more information.