Spell Mastery
You have mastered a small handful of spells, and can prepare these spells without referencing your spellbooks at all.
Prerequisite: 1st-level wizard.
Benefit: Each time you take this feat, choose a number of spells that you already know equal to your Intelligence modifier. From that point on, you can prepare these spells without referring to a spellbook.
Normal: Without this feat, you must use a spellbook to prepare all your spells, except read magic.
Source: Pathfinder Core Rulebook, p. 134