Por que precisamos formatar um cartão de memória antes de usá-lo?
Para gravar dados do usuário (arquivos ou diretórios) em um cartão de memória (ou outros tipos de dispositivos de armazenamento), precisamos ter um Sistema de arquivos para receber os dados.
A formatação prepara o meio de armazenamento para receber arquivos e adiciona um sistema de arquivos.
O que é um sistema de arquivos?
In computing, a file system or filesystem is used to control how data is stored and retrieved.
Without a file system, information placed in a storage medium would be one large body of data with no way to tell where one piece of information stops and the next begins.
By separating the data into pieces and giving each piece a name, the information is easily isolated and identified.
Fonte Sistema de arquivos
O que um formato realmente faz?
Disk formatting is the process of preparing a data storage device such as a hard disk drive, solid-state drive, floppy disk or USB flash drive for initial use. In some cases, the formatting operation may also create one or more new file systems.
The first part of the formatting process that performs basic medium preparation is often referred to as "low-level formatting".
Partitioning is the common term for the second part of the process, making the data storage device visible to an operating system.
The third part of the process, usually termed "high-level formatting" most often refers to the process of generating a new file system.
In some operating systems all or parts of these three processes can be combined or repeated at different levels and the term "format" is understood to mean an operation in which a new disk medium is fully prepared to store files.
Fonte Formatação de disco