Nokia Lumia 520 runs on Windows whereas Karbonn Titanium S5 runs on Android. Karbonn Titanium S5 Comes with a 1.2 GHz Quad Core processor, allowing you to do better multitasking than the Nokia Lumia 520 which comes with a 1 GHz Dual Core processor. Multiple core processor (Dual and Quad core) helps the device multitask better. Both the devices have 3G network compatibilty. Karbonn Titanium S5 supports Dual SIM whereas Nokia Lumia 520 doesn't support Dual SIM.
Display (& Touch)
Both the devices have Capacitive touchscreen. Capacitive touchscreens give better accuracy and control than Resistive touchscreens and they respond pretty well even to the slightest of touches. To learn more about touchscreens, click here. Coming to the display, Karbonn Titanium S5 comes with a 5 inches screen that is bigger than Nokia Lumia 520's 4 inches IPS LCD screen. To learn more about display types and technology, click here. The Karbonn Titanium S5 comes with a screen that has a higher screen resolution as compared to the screen resolution in Nokia Lumia 520. Higher the resolution, more detailed and clear the display is. Texts and other content appear much sharper in high resolution displays.
Camera & Storage
Karbonn Titanium S5 has a better Megapixel rating for the camera (8 MP) than Nokia Lumia 520 (5 MP). Nokia Lumia 520 does not have a front facing camera, whereas Karbonn Titanium S5 comes with a secondary (front facing) camera enabling you to do video chats. Both the devices have MicroSD card slot for memroy expansion.
Design and Portability
Nokia Lumia 520 is very heavy as compared to Karbonn Titanium S5.