I found few budget phones are releasing with true octa core.What does it mean? I read that the powerful dual core snapdragon phone is snappier than the quadcore phone of mediatek processor. Is it true? I also read that from ics only android supports dual core. Is the latest kitkat version is made to support octa core?
A true octa-core is basically a processor either with homogenous or heterogeneous multiprocessing architecture.
The processor in the Galaxy S4(Exynos 5410) for example (intl. edition) has 8 cores based on the ARM big.LITTLE architecture wherein 4 cores are slower with low-power and 4 are faster with relatively higher power consumption. Under this scheme two possibilities are there:
Only homogenous multiprocessing, For example in Galaxy S4. This allows only 4 cores to run at a time out of a total of 8. The processor can control which 4 run but all 8 cannot be utilized together.
Heterogeneous multiprocessing, For example in Galaxy S5. This allows all the 8 cores i.e the low power as well as high power cores to run together effectively increasing the maximum achievable performance of the SoC.
MediaTek's processor is also based on Homogenous Multiprocessing but has 8 homogenous cores instead of 4+4 different ones. This allows these cores to operate in coalition with each other without the heterogeneous architecture.
As far as fast or slow goes it depends on the FLOPS which the processor can achieve.
In this case, Mediatek's processor usually has a slower clock speed than Qualcomm's processor and a different architecture as well. Thus it's impossible to make a direct comparison of two processor without either a benchmarking software or a datasheet, but in general Qualcomm's latest top of the line processors are better than Mediatek's and this is despite additional cores.
One more reason which exists for this performance parity is that not all applications are built to utilize multiple cores i.e parallel processing. If you want more information regarding the same, consider reading this wiki article on Amdahl's Law.