Transcript Slide 1

Introduction to hard disk drive
Conference 2
From: Wikipedia, the free
encyclopedia
Architecture
• The motor has an external rotor; the stator windings are
copper-colored.
• The spindle bearing is in the center.
• To the left of center is the actuator with a read-write head
under the tip of its very end (near center); the orange
stripe along the side of the arm, a thin printed-circuit cable,
connects the read-write head to the hub of the actuator.
• The flexible, somewhat 'U'-shaped, ribbon cable barely
visible below and to the left of the actuator arm is the
flexible section, one end on the hub, that continues the
connection from the head to the controller board on the
opposite side.
Architecture
• The head support arm is very light, but also rigid; in
modern drives, acceleration at the head reaches 250
g's.
• The silver-colored structure at the upper left is the top
plate of the permanent-magnet and moving coil
"motor" that swings the heads to the desired position.
• Beneath this plate is the moving coil, attached to the
actuator hub, and beneath that is a thin neodymiumiron-boron (NIB) high-flux magnet.
• That magnet is mounted on the bottom plate of the
"motor".
Architecture
• The coil, itself, is shaped rather like an arrowhead, and
made of doubly-coated copper magnet wire.
• The inner layer is insulation, and the outer is thermoplastic,
which bonds the coil together after it's wound on a form,
making it self-supporting.
• Much of the coil, sides of the arrowhead, which points to
the actuator bearing center, interacts with the magnetic
field to develop a tangential force to rotate the actuator.
• Considering that current flows (at a given time) radially
outward along one side of the arrowhead, and radially
inward on the other, the surface of the magnet is half N
pole, half S pole; the dividing line is midway, and radial.
Capacity and access speed
• Using rigid disks and sealing the unit allows
much tighter tolerances than in a floppy disk
drive.
• Consequently, hard disk drives can store much
more data than floppy disk drives and can
access and transmit it faster.
Capacity and access speed
• As of January 2008:
– A typical desktop HDD, might store between 120
and 300 GB of data (based on US market data[10]),
rotate at 7,200 revolutions per minute (RPM) and
have a media transfer rate of 1 Gbit/s or higher. (1
GB = 109 B; 1 Gbit/s = 109 bit/s)
– The highest capacity HDDs are 1 TB[11].
Capacity and access speed
– The fastest “enterprise” HDDs spin at 10,000 or 15,000
rpm, and can achieve sequential media transfer
speeds above 1.6 Gbit/s.[12] Drives running at 10,000
or 15,000 rpm use smaller platters because of air drag
and therefore generally have lower capacity than the
highest capacity desktop drives.
– Mobile, i.e., laptop HDDs, which are physically smaller
than their desktop and enterprise counterparts, tend
to be slower and have less capacity. A typical mobile
HDD spins at 5,400 rpm, with 7,200 rpm models
available for a slight price premium. Because of the
smaller disks, mobile HDDs generally have lower
capacity than the highest capacity desktop drives.
Capacity and access speed
• The exponential increases in disk space and data access speeds of
HDDs have enabled the commercial viability of consumer products
that require large storage capacities, such as digital video recorders
and digital audio players.[13] In addition, the availability of vast
amounts of cheap storage has made viable a variety of web-based
services with extraordinary capacity requirements, such as free-ofcharge web search and email (Google, Yahoo!, etc.).
• The main way to decrease access time is to increase rotational
speed, while the main way to increase throughput and storage
capacity is to increase areal density. A vice president of Seagate
Technology projects a future growth in disk density of 40% per
year.[14] Access times have not kept up with throughput increases,
which themselves have not kept up with growth in storage capacity.
Capacity and access speed
• As of 2006, some disk drives use perpendicular
recording technology to increase recording
density and throughput.[15]
• The first 3.5" HDD marketed as able to store 1 TB
was the Hitachi Deskstar 7K1000. It contains five
platters at approximately 200 GB each, providing
935.5 GiB of usable space.[16] Hitachi has since
been joined by Samsung (Samsung SpinPoint F1,
which has 3 × 334 GB platters), Seagate and
Western Digital in the 1 TB drive market.[17][18]
Capacity and access speed
Form factor
Width
Largest capacity
Platters (Max)
5.25" FH
146 mm
47 GB[19] (1998)
14
5.25" HH
146 mm
19.3 GB[20] (1998)
4[21]
3.5"
102 mm
1 TB[16] (2007)
5
2.5"
69.9 mm
500 GB[22] (2008)
3
1.8" (PCMCIA)
54 mm
160 GB[23] (2007)
1.8" (ATA-7 LIF)
53.8 mm
1.3"
36.4 mm
40 GB[24] (2008)
1
Capacity measurements
• The capacity of an HDD can be calculated by
multiplying the number of cylinders by the
number of heads by the number of sectors by the
number of bytes/sector (most commonly 512).
• Drives with ATA interface bigger and more than
eight gigabytes behave as if they were structured
into 16383 cylinders, 16 heads, and 63 sectors,
for compatibility with older operating systems.
Capacity measurements
• Unlike in the 1980s, the cylinder, head, sector
(C/H/S) counts reported to the CPU by a modern
ATA drive are no longer actual physical
parameters since the reported numbers are
constrained by historic operating-system
interfaces and with zone bit recording the actual
number of sectors varies by zone.
• Disks with SCSI interface address each sector with
a unique integer number; the operating system
remains ignorant of their head or cylinder count.
Capacity measurements
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