Most mechanical storage systems are simple, composed either of a single sequence of stored objects (like a bookshelf) or a series of sequences, one level deep (like a file cabinet).

• 大多数机械存储系统是简单的，不是由简单的存储对象序列（诸如书架）组成的。 即使是一系列的序列，深度只有一层（好比文件柜）。