The spellbook of a magus is effectively the same as that of a wizard. Wizards and magi can lears spells from each others' books, which implies that they have the same costs/page length/etc.
A magus must study his spellbook each day to prepare his spells. He cannot prepare any spell not recorded in his spellbook except for read magic, which all magi can prepare from memory. A magus begins play with a spellbook containing all 0-level magus spells plus three 1st-level magus spells of his choice. The magus also selects a number of additional 1st-level magus spells equal to his Intelligence modifier to add to his spellbook. At each new magus level, he gains two new magus spells of any spell level or levels that he can cast (based on his new magus level) for his spellbook. At any time, a magus can also add spells found in other spellbooks to his own (see Arcane Spells).
A magus can learn spells from a wizard's spellbook, just as a wizard can from a magus's spellbook. The spells learned must be on the magus spell list, as normal. An alchemist (see the Alchemist description) can learn formulae from a magus's spellbook, if the spells are also on the alchemist spell list. A magus cannot learn spells from an alchemist.
Witches don't have spellbooks. They learn their spells from their familiars.
A witch must commune with her familiar each day to prepare her spells. Familiars store all of the spells that a witch knows, and a witch cannot prepare a spell that is not stored by her familiar. A witch's familiar begins play storing all of the 0-level witch spells plus three 1st-level spells of the witch's choice. The witch also selects a number of additional 1st-level spells equal to her Intelligence modifier to store in her familiar. At each new witch level, she adds two new spells of any spell level or levels that she can cast (based on her new witch level) to her familiar. A witch can also add additional spells to her familiar through a special ritual...
Alchemists don't cast spells or have spellbooks. They do have a formula book that's the equivalent to a spellbook.
An alchemist may know any number of formulae. He stores his formulae in a special tome called a formula book. He must refer to this book whenever he prepares an extract but not when he consumes it. An alchemist begins play with two 1st-level formulae of his choice, plus a number of additional forumlae equal to his Intelligence modifier. At each new alchemist level, he gains one new formula of any level that he can create. An alchemist can also add formulae to his book just like a wizard adds spells to his spellbook, using the same costs, pages, and time requirements. An alchemist can study a wizard's spellbook to learn any formula that is equivalent to a spell the spellbook contains. A wizard, however, cannot learn spells from a formula book. An alchemist does not need to decipher arcane writings before copying them.