A storage device whose contents cannot is modified,except by a particular user,or when operating under particular condition,for example,a storage device in which writing is prevented by a lockout.

• 内容不能进行修改的一种存储设备，除非是一个特殊用户或者在特定条件下方可进行写操作。例如，通过锁定而防止写入内容的存储设备。同fixed storage, permanent storage, read only memory。