Hard Disk Storage
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Objectives
• In this chapter, you will:
– Understand how hard drives read and write data
– Know the difference between tracks, sectors, and cylinders
– Understand the difference between high-level and low-level
formatting
– Identify the major internal components and understand the
workings of a typical hard drive
– Identify cables and connectors used with hard drives
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Definition
• A hard disk drive is a
sealed unit that a PC uses
for nonvolatile data
storage.
• A hard disk drive contains
rigid, disk-shaped platters,
usually constructed of
aluminum or glass
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Drive Operation
• The basic physical construction of a hard disk drive consists of
spinning disks with heads that move over the disks and store data in
tracks and sectors.
• The heads read and write data in concentric rings called tracks, which
are divided up into segments called sectors, which normally store 512
bytes each.
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Drive Operation
• One side of a platter is called
a “head”.
• Hard drives can have different
numbers of platters,
depending on their design
and storage capacity.
• On the heads, you will see
concentric rings (tracks) and
pieces of rings (sectors) just
like on the floppy disks.
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Drive Operation
• Many hard drives today use a technology
called “zone bit recording”
• Which enables the hard drive to have
more sectors on the outer tracks, where
there is more room than on the inner
tracks.
• This allows more room for storage
Original
Zone Bit
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Drive Operation
• Another logical unit of a
hard drive is the cylinder.
• Let’s say we have a disk
drive with three platters.
Imagine passing a cylinder
down through both sides
of each platter (6 tracks).
• These 6 tracks make up a
logical cylinder on the disk.
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Computer Data Storage
• The read/write head on the drive moves very close to the spinning disk
as it goes by and writes to specific concentric rings on the disk, called
tracks.
• The electrical particles on the disk are arranged according to the charge
given to them by the head.
• The head can read the magnetic data as it passes by, or write to it by
using an electrical charge.
• Preparing a disk drive for data
storage involves three steps:
– Low-Level formatting (LLF)
– Partitioning
– High-level formatting (HLF)
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Low Level Formatting
Sector
• Low level formatting
marks the tracks and
sectors of the disk.
• A sector is a small section
of a track that stores 512
Bytes of information
Track
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Partitioning
• Partitioning a disk is the act of
defining areas of the disk for an
operating system to use.
• Partitioning is required because a
hard disk is designed to be used
with more than one operating
system.
• Partitioning enables a single hard
disk drive to run more than one
type of operating system (dual
boot), or it can enable a single
operating system to use the disk as
several volumes or logical drives.
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Partitioning
• You decide you want to break the 10GB space into
three logical partitions: one with 5GB of space, one
with 3GB, and one with 2GB.
• The operating systems will logically view these three
partitions as three separate drives and gives them
separate drive letters C:, D:, and E:.
• Physically all you have is one hard drive with three
logical drives.
• Hard drive partitions must always begin at C:;
because the A: and B: drives are reserved for
floppies.
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High Level Formatting
• A part of the system area is called the “Master boot sector”.
– This is the process of creating the disk's logical structures such as the
file allocation table and root directory.
• The Master boot sector is:
– Always the first sector (sector 0) of the first track (track 0) of the first
cylinder (cylinder 0) disk.
– 512 bytes long, just like any other sector
– Contains information on all logical drives, regardless of whether they
are bootable.
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High Level Formatting
• Formatting also creates the root directory.
(C:\)
• If the disk is to be made bootable,
COMMAND.COM and two system files
(io.sys and msdos.sys) must be in the root
directory of the bootable drive.
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Components
• The basic components of a typical
hard disk drive are as follows:
– Disk platters
– Read/write heads
– Head actuator mechanism-Spindle
motor (inside platter hub)
– Logic board (controller or Printed
Circuit Board)
– Cables and connectors
– Configuration items (such as
jumpers or switches)
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The platters, spindle motor,
heads, and head actuator
mechanisms usually are
contained in a sealed
chamber called the Head
Disk Assembly (HDA).
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Platters
• A hard disk drive has one or more platters, or disks.
• Most hard disk drives have two or more platters, the number of platters
a drive can have is limited by the drive's vertical physical size.
• Platters have traditionally been made from an aluminum/magnesium
alloy, which provides both strength and light weight. However,
manufacturers' desire for higher and higher densities and smaller drives
has led to the use of platters made of glass.
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Recording Media
• No matter which substrate is used, the platters are covered with a
thin layer of a magnetically retentive substance, called the medium,
on which magnetic information is stored. Two popular types of
magnetic media are used on hard disk platters:
-Oxide medium
-Thin-film medium
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Drive Operation: magnetization
• HDDs record data by magnetizing ferromagnetic material directionally, to
represent either a 0 or a 1 binary digit.
• The Co-based alloy thin films are polycrystalline and the size of grains has
an order of 10 nm.
• In practice, a group of grains (about 100) are magnetized as one bit.
• The read-and-write head is used to detect and modify the magnetization of
the material immediately under it. There is one head for each magnetic
platter surface on the spindle, mounted on a common arm.
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Read Write Heads
• A hard disk drive usually has one read/write head for each platter surface
These heads are connected, or ganged, on a single movement
mechanism.
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Air Filters
• Nearly all hard disk drives have
two air filters.
• One filter is called the
recirculating filter, and the other
is called either a barometric or
breather filter.
• These filters are permanently
sealed inside the drive and are
designed never to be changed for
the life of the drive.
HD heads are kept from contacting the platter surface by the
air that is extremely close to the platter; that air moves at, or
close to, the platter speed.
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Spindle Motors
• The motor that spins the platters is called the spindle
motor because it is connected to the spindle around
which the platters revolve. Spindle motors in hard disk
drives are always connected directly; no belts or gears are
involved.
• The spindle motor also must be precisely controlled for
speed. The platters in hard disk drives revolve at speeds
ranging from 3,600 rpm to 15,000 rpm or more.
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Logic Boards
• All hard disk drives have one or more logic boards mounted on them.
• The logic boards contain the electronics that control the drive's
spindle and head actuator systems and present data to the controller
in some agreed-upon form.
• On ATA drives, the boards include the controller itself, whereas SCSI
drives include the controller and the SCSI bus adapter circuit.
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Cables and Connectors
• Hard disk drives typically have several connectors for interfacing to the
computer, receiving power, and sometimes grounding to the system
chassis. Most drives have at least these three types of connectors:
-Interface connector(s)
-Power connector
-Optional ground connector (tab)
• The interface connectors are the most
important because they carry the data
and command signals between the
system and the drive.
• The power connector is usually the same four-pin type that is used in
floppy disk drives, and the same power-supply connector plugs into it.
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Configurations Items
• To configure a hard disk drive for
installation in a system, you
usually must set several jumpers
(and, possibly, terminating
resistors) properly.
• Master, Slave, and Cable Select
are different configurations you
can select with jumpers
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IDE Hard Drive
• Originally hard drives required a separate plug-in controller to
connect the drive to the rest of the system.
• IDE: Integrated Device Electronics.
– Today’s hard drives have the controller built onto the drive rather than using a
separate controller. This shortens the distance between the controller and the
hard drive and eliminates the interference problem inherent with older drives.
– It is the most widely-used hard drive interface on the market.
– The fancy name refers to how the IDE technology "integrates" the electronics
controller into the drive itself.
• The IDE interface, which could only support drives up to 540
MB has been replaced by the superior EIDE (Enhanced-IDE)
technology which supports over 50 GB and allows for over
twice as fast data transfer rates.
• The other most common hard drive interface is SCSI, which is
faster than EIDE, but usually costs more.
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ATAPI Devices
• ATA: AT Attachment.
– The specification, formulated in the 1980s by a consortium of
hardware and software manufacturers, that defines the IDE drive
interface.
– AT refers to the IBM PC/AT personal computer and its bus
architecture. IDE drives are sometimes referred to as ATA drives or AT
bus drives.
• Shortly after the introduction of the IDE drive, CD ROM
drives were being added to the system to add multi-media
capabilities.
– With the new ATAPI (Advanced Technology Attachment Packet
Interface) standard devices like CD ROM drives, Tape Drives, Zip
Drives, and DVD Drives could share the same IDE hard drive cable.
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SATA Drives
•
•
•
Serial ATA was designed to replace the older ATA (AT
Attachment) standard (also known as EIDE).
It is able to use the same low level commands, but serial ATA
host-adapters and devices communicate via a high-speed serial
cable over two pairs of conductors.
Serial ATA has distinct key advantages over its predecessor.
Cables are very thin with small 7-pin connectors. They can be
up to 3 feet (1 meter) in length, and are easily routed to stay
out of the way allowing maximum airflow inside the case.
–
•
•
ATA cables limited to 18 inches (46 cm) in length often made connections
difficult and also clogged cases blocking airflow, while cooling has become
crucial.
SATA also has a far lower power requirement of just 250 mV
compared to PATA's 5-volt requirement, and with chip core
voltages declining, this speaks well of SATA's future.
First generation SATA has a maximum transfer rate of 150 MBps,
and second generation SATA delivers 300 MBps. A third
generation SATA set for 2009, "SATA 6Gb/s" will deliver roughly
twice the speed of the previous SATA iteration.
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SATA Drives
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Floppy
8-inch, 5¼-inch, and 3½inch floppy disks
• A floppy disk is a data storage
medium that is composed of a disk of
thin, flexible ("floppy") magnetic
storage medium encased in a square
or rectangular plastic shell.
• Invented by IBM, floppy disks in 8inch (200 mm), 5¼-inch (133.35 mm),
and 3½-inch (90 mm) formats
enjoyed many years as a popular and
ubiquitous form of data storage and
exchange, from the mid-1970s to the
late 1990s.
• They have now been largely
superseded by USB flash drives
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Floppy
Disk format
8-inch - IBM 23FD (read-only)
8-inch - SSSD
IBM 33FD / Shugart 901
8-inch - DSSD
IBM 43FD / Shugart 850
8-inch DSDD
IBM 53FD / Shugart 850
5¼-inch DD
3½-inch
HP single sided
Year introduced
Formatted
Storage capacity
in KB (1024 bytes) if not stated
Marketed
capacity¹
1971
79.7
?
1973
237.25
3.1 Mbits unformatted
1976
500.5
6.2 Mbits unformatted
1978
980
- 1200 (MS-DOS FAT)
360 or 800
1982
280
264 kB
3-inch
1982
360
125 kB
3½-inch (DD at release)
1984
720 (400 SS, 800 DS on Macintosh,
880 DS on Amiga)
1 MB
1,182,720 bytes
1.2 MB
?
?
?
1.44 MB (2.0 MB
unformatted)
2.88 MB
21 MB
120 MB
240 MB
150/200 MB
5¼-inch HD
1977
1982 YE Data YD380
3-inch DD
2-inch
5¼-inch Perpendicular
1984
1985
1986
720
720
100 MB
3½-inch HD
1987
1440
3½-inch ED
3½-inch Floptical (LS)
3½-inch LS-120
3½-inch LS-240
3½-inch HiFD
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1987
1991
1996
1997
1998/99
2880
21000
120.375 MB
240.75 MB
150/200 MB
1.2 MB
360 KB
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Floppy
• The A: and B: drives on a desktop
computer are reserved in the BIOS
for floppy disk drives.
– As most computers only come with one
floppy disk drive only the A: drive will be
visible in file explorer.
– If a second floppy disk drive is fitted then
both A: and B: drives will be visible.
Ribbon cable used
to connect floppy.
To indicate which
end of the cable is
pin 1 on a drive
cable, a stripe is
drawn on the edge
of the cable.
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