All this data is potentially out of date, and should be taken with a truckload of salt
When launched from the bay, drones require bandwidth; if there is insufficient bandwidth remaining, drones are not launched thus remaining in the drone bay. This functions as a secondary limit to the usage of drones and can serve to limit damage just as less power grid and CPU limits the size and number of weapons on a ship. Bandwidth is given in megabits per second (Mbit/sec) in multiples of 5Mbit/sec. Most ships have bandwidth equal to their drone bay size and can deploy as many drones as they can store, but some ships, mainly drone boats, have less bandwidth than drone bay space, and are thus incapable of launching all of their drones at once.
The amount of drone bay space and bandwidth varies by ship with larger ships generally having more. In addition different factions have differing amounts of drone usage and space. Gallente ships generally have the largest drone bays and bandwidth. Some Gallente ships are specialized 'drone boats', designed specifically for the deployment and use of drones. They are able to use a large number of drones and have bonuses to drone usage. The Amarr Empire also fields some ships with spacious drone bays, but not as many, or as large as the Gallente ships. Caldari ships have the smallest drone bays with some ships lacking drone bays entirely.