Why do you need blocks when you have sectors and why is the block size a multiple of sector size?

Question

On reading through disc structure, I come across this statement that blocks size is a multiple of sector size. First thought is why do u even need blocks when u have sectors, and secondly why is the block size a multiple of sector like 1,2,4?

Why can't it be half of sector? What's the rationale here? This is not for homework.

Answer 1

Block is an abstraction of filesystems. All filesystem operations can be accessed only in multiple of blocks. In other terms , smallest logically addressable unit to filesystem is block , not a sector.

The smallest addressable unit on a block device is a sector.The sector size is physical property of a block device and is the fundamental unit of all block devices.

Most block devices have 512-byte sectors (although other sizes are common. For example, some CD-ROM discs have 2-kilobyte sectors) while block sizes are commonly of size 512 bytes , 1 KB or 4KB. This is the reason block size is a multiple of sector.

Answer 2

Early in the computing industry, the term "block" was loosely used to refer to a small chunk of data. Later the term referring to the data area was replaced by sector, and block became associated with the data packets that are passed in various sizes by different types of data streams.

read more here: http://en.wikipedia.org/wiki/Disk_sector