A mammography unit is a box-shaped machine that produces X-rays for breast exams. It has several components, including: 
X-ray tube
Contains a cathode and anode, with the cathode at the chest wall and the anode on the opposite side. The anode rotates to allow higher mA and shorter exposure times. 
Breast compression device
Holds and compresses the breast to reduce the thickness of tissue that the X-rays must pass through. This improves image quality, reduces scattered radiation, and holds the breast still. 
Detector
Captures the X-ray image as either a photographic film plate or a solid-state detector. The solid-state detector transmits electronic signals to a computer to form a digital image. 
Accessories
Limit X-ray exposure to the breast. 
Mammography units can also be mobile, which can help increase participation in breast screenings by reaching women in places with low rates. 
Some things to consider when comparing mammography units include:
Generator type
Three-phase and constant potential generators may offer shorter exposure times, more adequate exposure, and a longer tube life.
Tube voltage control
Screen-film mammography should use increments of 1 kVp, while xeromammography should use increments of 2 kVp.
Tube loading limitations
A mammography unit with a lower mA output may require longer exposure times.
Phototimer capability
Can reduce exam time, facilitate proper exposure, and reduce radiation dose.