Spell slots

Advanced d20 Magic » Spell slots
Typically, Bards and Sorcerers are assigned Spell Slots by the class which provides the spellcasting ability. This measures the character's ability to learn spells. Each spell requires a number of slots to learn, ranging from only one slot for a simple spell, to four slots for the most powerful. The number of spell slots required to learn a spell is listed in its description.
Under the standard approach, divine spellcasters do not have spell slots, but can learn all of the spells on their spell list automatically, from the beginning. To compensate for this advantage, divine spells require a full round to cast rather than just one action. That is, a casting a divine spell is all that a character may do for one round; the character will continue casting until his Initiative the following round.
Wizards also don't use spell slots, since wizards can learn an unlimited number of spells. Unlike the divine casters, wizards must still study to learn spells.
Bards receive 3 spell slots per level, sorcerers receive 4 spell slots per level.
If the GM is unsatisfied with unlimited divine caster spell knowledge or wizard potential, then spell slots may also be used for these classes. In this case, wizards receive 10 spell slots per level, clerics and druids receive 8 spell slots per level, and paladins and rangers receive 2 spell slots per level.