What is the main difference between sars and pneumonia?

None: Sars is a viral pneumonia with systemic systems - i.e. It is a specific kind of pneumonia. Pneumonia is simply any infection involving the lung; fungi, viri, and bacteria can all cause pneumonia in humans.

SARS is a type : Pneumonia is any infection of the lungs. Sars is a particularly severe pneumonia that can cause respiratory failure and require life support. It is caused by a particular virus. Because it is caused by a virus there is no standard antibiotic to treat it and the treatment is to simply support the patient until it resolves.