Eye of the Beholder don't have only 4 classes!!!
Thief and Rogue are different
Ranger and Archer are different
Fighter , Warrior and Paladin are different
Cleric and Paladin are different
Thief: Disarm traps , unlock doors , unblock chests
Rogue: Made backstub , silent move , hide in shadows
Fighter: Wears light armour and heavy armour keep sword , and axe and spear and mace
Paladin: Wears light armour . keep spear , make few cleric spells (Lay of hands or few heal)
Warrior: Wears light armour and heavy armour , keep axe , sword , not spear and make and charge (Critical Hit)
Barbarian: Wears only heavy armour , keep only axe , make charge (Critical hit)
Mage: Learn spells during the adventure , don't have spells after creation , keeps mace , mage need spell book to cast
Wizzard , Born as spell caster and cast spells , have spells after creation , keeps stuff , wizzard don't need spell book to cast
Cleric: Make heal spells , and counter spells , keeps mace and stuff , makes potions. Need holy cross to make spells
Archer: wears light armour , or leather only , keep bow and can keep and short weapons , not spears and long sword.
Ranger: wears light armour , or plate male or leather. Keep bow and can transform to some animal , like bear or wolf , can comunicate with animals.
Necromancer: Wears light armour , makes only undead spells , can make summon spells , keeps spellbook , keeps stuff , can make teleportation , can control an undead creature and can make and raise dead spells.(Like Cleric)
Also there is and the Warrior Priest , is similar to paladin , keeps only stuff and lond sword , wears plate male and chain male and light armour.
AD&D Second edition rules. This is a nice information of classes about Dungeons And Dragons or Generic RPG.