When i entered #fdisk -l in unbuntu 9.04

following is the result

```
Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0xe9ffe9ff

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1       10199    81923436    7  HPFS/NTFS
/dev/sda2           10200       19457    74364885    f  W95 Ext'd (LBA)
/dev/sda5           10200       19457    74364853+   7  HPFS/NTFS

Disk /dev/sdb: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0xf16cf16c

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1       10199    81923436    7  HPFS/NTFS
/dev/sdb2           10200       19457    74364885    f  W95 Ext'd (LBA)
/dev/sdb5           10200       19457    74364853+   7  HPFS/NTFS

```

But somewhat i can't understand following result.

What is sdb?
I searched through internet and knew 'sdb' is the primary slave.
What is the primary slave though? What is the primary master? What is different between the two?

and why sda2, sda5 start at same location?