Hard disk drives use magnetic platters to store data in binary form. An actuator uses a read-write arm and head to read and write data by detecting transitions in magnetic fields on the platters. Data is organized into tracks and sectors for efficient access. Performance is determined by seek time, latency, and transfer time. Common interfaces are PATA, SATA, SCSI, and USB. RAID configurations like striping and mirroring provide redundancy and performance benefits. A disk controller manages communication and data movement between the disk and host system.

1. Hard Disk Drives

3. HDD Parts
1. Actuator
2. Read-write arm swings read-write head back and forth across
platter.
3. Central spindle allows platter to rotate at high speed.
4. Magnetic platter stores information in binary form.
5. Plug connections link hard drive to circuit board in personal
computer.
6. Read-write head is a tiny magnet on the end of the read-write
arm.
7. Circuit board on underside controls the flow of data to and from
the platter.
8. Flexible connector carries data from circuit board to read-write
head and platter.
9. Small spindle allows read-write arm to swing across platter.

4. IBM’s DASD

6. HDD Data Access Method
• HDD records data by magnetizing a thin film of
ferromagnetic material on a disk.
• Sequential changes in the direction of
magnetization represent binary data bits.
• The data is read from the disk by detecting the
transitions in magnetization.

9. HDD Data organization

10. HDD Data organization
• Each platter is consist of no. of invisible concentric
circles which are called Tracks.
• A set of such corresponding tracks in all the surfaces is
called Cylinder.
• Tracks are further divided into Sectors. (512 bytes)
• Group of sectors on same track can be identified as
Clusters. (64 sectors in 1 cluster)
• The Outer tracks has greater circumference then inner
tracks but each track consist of same no. of characters.
Hence the data density of outer tracks is less as
compare to inner tracks.

12. Zone Bit Recording

15. HDD Performance Characteristics
• Seek Time
– Time to move from current track to desired track
• Latency
– Time to reach to the start of the sector
• Transfer Time
– Time to access data
• Access Time
= (Seek time) + (Latency) + (Transfer time)

16. Access Time = (Seek time) + (Latency) + (Transfer time)

17. HDD Interfaces
• PATA/IDE
• SATA
• USB/Firewire
• SCSI
• RAID
• SSD

18. HDD Interfaces
• PATA/IDE/EIDE
– Since 1986
– Parallel signaling (multiple bits simultaneously)
– Max Transfer speed : 133MB/s
– Advantage: Compatible, cost effective
– Disadvantages: slow data transmission speed,
short cable length, fewer connected devices, no
support for hot swap, poor upgrading ability of
interface speed.

19. HDD Interfaces
• SATA
– Serial signaling (bit by bit)
– Speed up to 300 MB/s
• USB/Firewire – For external hard disks
• SCSI
– Small Computer System Interface
– Connect multiple devices simultaneously internally as well
as externally
– Speed up to 320MB/s
– Widely replaced by USB Standards

20. HDD Interfaces
• RAID
– Redundant Array of Independent Disks
– Major 3 approaches
• Striping
• Mirroring
• Error Handling

22. RAID 0
Striping
RAID 1
Mirroring
RAID 2
Striping and error correcting
mechanism striped

23. RAID 3
Byte level striping
RAID 4
Block level Striping
RAID 5
Parity interleaving

25. Hard Disk Controller

26. provide a
standard
protocol for the
Disk Drive to talk
to a host system
contain logic for
moving data to and
from the host sequencer pulls
data from
registers, data
buffers, and the
ECC block
general logic for
spinning of the discs
and in the positioning
of the actuator