1) The possessive case indicates that one noun belongs to another noun or somehow associates with it. It's the most commonly used form of genitive case, but not the only one. The nouns can refer to people or any other objects. 2) The word "дедов" in "дедов карандаш/дедова книга" etc is an adjective and not a noun in possessive form. Adjectives correspond with nouns in gender and number. The possessive form would be "карандаш деда", "книга деда" etc

compare - дедОВА книга( the related word is in female gender ) and книга деда ( genitive case ) ДедOВ костюм ( male gender) ДедОВЫ книги ( both genders in plural ) no difference in meaning they are just different grammar structures in colloquial speech possessive case is preferable on my opinion

Thank you! Alexander^_^

What is the difference between 1) дедова книга and 2) книга деда? When you use the first case you note not just a physical belonging/legal rights of the book, but you note also a mental/soul "relation". For ex, if grandfather will give a book as a present to grandmother it will be книга бабушки but will probably remain дедова книга.