DSLR vs Mirrorless camera ...

NASIM MANSUROV, PHOTOGRAPHY LIFE:

"DSLR cameras by design have some inherent flaws and limitations. Part of it has to do with the fact that SLR cameras were initially developed for film. When digital evolved, it was treated just like film and was housed in the same mechanical body. Aside from the circuitry required for a digital sensor and other electronics, new digital film media and the back LCD, the rest of the SLR components did not change. Same mechanical mirror, same pentaprism/optical viewfinder, same phase detection system for autofocus operation. While new technological advances eventually led to extending of features of these cameras (In-camera editing, HDR, GPS, WiFi, etc), DSLRs continued to stay bulky for a couple of reasons. First, the mirror inside DSLR cameras had to be the same in size as the digital sensor, taking up plenty of space. Second, the pentaprism that converts vertical rays to horizontal in the viewfinder also had to match the size of the mirror, making the top portion of DSLRs bulky."

Learn more, here.