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

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Original

Zone Bit

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 datastorage involves three steps:– Low-Level formatting (LLF)– Partitioning– High-level formatting (HLF)

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Low Level Formatting

• 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

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Track

Sector

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).

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.

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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.

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• 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 8-inch (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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8-inch, 5¼-inch, and 3½-inch floppy disks

Floppy

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Disk format Year introducedFormattedStorage capacityin KB (1024 bytes) if not stated

Marketedcapacity¹

8-inch - IBM 23FD (read-only) 1971 79.7 ?

8-inch - SSSDIBM 33FD / Shugart 901 1973 237.25 3.1 Mbits unformatted

8-inch - DSSDIBM 43FD / Shugart 850 1976 500.5 6.2 Mbits unformatted

8-inch DSDDIBM 53FD / Shugart 850 1977 980

- 1200 (MS-DOS FAT) 1.2 MB

5¼-inch DD 1978 360 or 800 360 KB3½-inchHP single sided 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

5¼-inch HD 1982 YE Data YD380 1,182,720 bytes 1.2 MB

3-inch DD 1984 720 ?2-inch 1985 720 ?5¼-inch Perpendicular 1986 100 MB ?

3½-inch HD 1987 1440 1.44 MB (2.0 MB unformatted)

3½-inch ED 1987 2880 2.88 MB3½-inch Floptical (LS) 1991 21000 21 MB3½-inch LS-120 1996 120.375 MB 120 MB3½-inch LS-240 1997 240.75 MB 240 MB3½-inch HiFD 1998/99 150/200 MB 150/200 MB

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.

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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.