磁盘空间划分的问题

["水静流深" <1248283536@qq.com>]

我在给磁盘划分区，请看

root@debian:/home/tiger# fdisk /dev/sdb

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to

         switch off the mode (command 'c') and change display units to

         sectors (command 'u').

Command (m for help): c

DOS Compatibility flag is not set

Command (m for help): u

Changing display/entry units to sectors

Command (m for help): n

Command action

   e   extended

   p   primary partition (1-4)

p

Partition number (1-4): 1

First sector (2048-7567359, default 2048): 

请问，default first sector 从2048开始，那1到2048的空间为何不可以使用？