I'm reading tutorials about PIC16F628A, I found that in all project they use a Crystal Oscillator, is it means that the PIC doesn't any internal clock and it cant run without an external Crystal Oscillator??
Internal and external oscillator options:
- Precision internal 4 MHz oscillator factory calibrated to ±1%
- Low-power internal 48 kHz oscillator
- External Oscillator support for crystals and resonators
source (3rd page) - http://ww1.microchip.com/downloads/en/DeviceDoc/40044F.pdf
All (or almost all) microcontrollers have internal clocks. Reasons for using external oscillators vary, but usually because they are more accurate and have higher selection of frequencies than internal RC oscillators. They are also cheap and do not take much place.
Before reading tutorials, you should become familiar at least with microcontroller capabilities by reading datasheets.