Depending upon the penetration power, there are two parts of X-rays
Hard X-rays
More penetration power
More frequency of the order of ≈ 1019 Hz
Lesser wavelength range (0.1Å - 4Å)
Soft X-rays
Less penetration power
Less frequency of the order of ≈1016 Hz
More wavelength range (4Å - 100Å)