Final answer:
A fixed length block of data in secondary memory is called a sector, which is a standard unit of storage on devices like hard drives and SSDs.
Step-by-step explanation:
A fixed length block of data that resides in secondary memory is a sector. Secondary memory, commonly referred to as external memory or auxiliary storage, typically includes devices like hard drives, solid-state drives, and magnetic tape systems. In these storage devices, data is organized into sectors, which are basic units of storage with a fixed capacity.
The size of a sector is determined by the physical geometry and the formatting of the disk, and it's often 512 bytes or, more recently, 4096 bytes in newer storage systems. When a computer reads or writes data, it does so in multiples of sector sizes to optimize memory access performance.