Computer Hard Drive

8/11/2019 Computer Hard Drive

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COMPUTER HARD DRIVE

Pham Ngoc Thai HoaDepartment of English

[email protected]


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CONTENT

Introduction to Hard drive

Hard drive basics

Capacity & Performance

Inside the hard drive

Storing the data

Manufacturers

More information


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INTRODUCTION TO

HARD DRIVE Commonly refered to:

hard disk, fixed disk

drive, HDD (Harddisk drive)

A common magneticstorage device that

reads and writes dataon metal disks inside a

sealed case.


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HARD DISK BASICS

The first was invented in 1956 byIBM with the RAMAC hard diskwith 20 platters which could store

100,000 bytes. In the 1980s, desktop computer

hard disks introduced with 5 MBusing 5.25 platters.

Todays hard disks have at least100,000 times more capacity.Platter sizes reduced to

3.5 for desktops 2.5 or 1.8 for laptops 1 for handheld devices


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A NOT-EVEN-ONE-INCH DISK

Toshiba introduced 1st0.85 hard drive withcapacity of 24 GB in 2005

Size: a postage stamp


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STANDARD ELECTRONIC

INTERFACE IDE (Integrated Drive Electronics): a standard electronic

interface used between a computer motherboard's datapaths or bus and the computer's disk storage devices. It

refers to the types of cables and ports. SATA (Serial ATAAdvanced Technology Attachment):

an IDE standard for connecting devices like optical drivesand hard drives to the motherboard.

IDE & SATA: interfaces for PCs.

SCSI (Small Computer System Interface): standardelectronic interface for servers (mainly) & powerfuldesktops.


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SATA vs. IDE


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CAPACITY & PERFORMANCE

Capacity: the number of bytes that a drive canhold

Capacity of typical PCs: 40GB1000GB Data stored on disks as files

Three ways to measure performance: Data rate: number of bytes per second that the drive

can deliver to CPU Seek time: Amount of time when CPU requests a file

& when the 1stbyte of the file is sent to CPU.

Disk Cache: 8Mb capacity


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INSIDE THE DISK: PHYSICAL

COMPONENTS Platters (a)

Read/Write heads

(u c/ghi) Spindle (trc)

Actuator (c cu

truyn ng) Electronics (mch

in)


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PLATTERS

Platter: A hard disk hasone or more platters - or

disks - and each platter

usually has a head on eachof its sides.

Modern drive: platters aremade of ceramic or glass

Magnetic coating coversplatters


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SECTOR & TRACK

Sector (Cung): A formattedsection of a circular magnetictrack used for storing data on adisk. (512 Bytes)

Track (Rnh): A formattedcircular magnetic storage areaon a disk.

Cluster (lin cung): the smallestlogical amount of disk spacethat can be allocated to hold afile.

Cylinder (Tr): All tracks withthe same radius are referred toas a cylinder.

Shaft (trc): The rotating part inthe center of a motor thattransfers power.


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READ/WRITE HEAD

A tiny electromagnetic coiland metal pole used to writeand read magnetic patterns ona disk.

Read/Write head mounted onarms which can move ittowards the central spindles ortowards the edge

As the read/write heads passover the spinning platters theymagnetize the surface in a

pattern which represents thedata in digital form.


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SPINDLE

The plattersaremounted on the spindle

which is turned by thedrive motor.

Most current hard disk

drives spin at between5,400 and 10,000 RPM.


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ACTUATOR


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HEAD SLIDER

Head slider: Read/Writeheads are too smalleachhead is mounted to a headslider (slider).

Function: Physically supportthe head & hold it in correct

position relative to the platteras the head floats over itssurface.

Each slider is mounted onto ahead arm to allow it to bemoved over the surface of the

platter to which it is mated.


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HEAD ARM

Thin pieces of metal, usually triangular in shape ontowhich the head sliders (carrying the read/write heads) are

mounted. Newer designs: replaced solid arms with structural shapesreduce weight & improve performance.


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HEAD ACTUATOR

The device used to position the head armsto different tracks on the surface of the

platter. Two kinds of actuators:

Stepper Motors(ng c bc)

First hard disksVoice Coils(ng dy)Modern hard disks


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STEPPER MOTORS vs. VOICE COILS


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VOICE COILS ACTUATOR

Voice coilmoves the head arms in andout over the surface of the platters, anda closed-loop feedback system called a

servo system (h thng ph)to positionthe heads directly over data tracks.

The voice coil works usingelectromagnetic attraction andrepulsion.

By controlling the current, the headsmove in or out more precisely than a

stepper motor. Voice coil" comes from theresemblance of this technology to thatused to drive audio speakers.

All PC hard disk voice coil actuatorsare rotary: the actuator changes

position by rotating on an axis.


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SERVO TECHNIQUES

Modern hard disks use voice coil actuatorsto position the heads on the surface of the

hard disk's platters. This actuatorservo system (a type of

closed-loop feedback system)


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THERMAL RECALIBRATION

Every few minutes, the heads are moved and thedistance between tracks measured.

This information is recorded in the drive's memory

& used to aid in positioning the heads whenreading or writing needs to be done.

When the recalibration occurs you can hear thedisk operate as if you were reading or writing to it,even if you are not.

Side-effect: if you attempt to access the disk whilea recalibration cycle is taking effect, there is aslight pause until it completes.


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STORING THE DATA

Data stored on surface ofplatter in sectors & tracks.

Sectors are often groupedtogether in clusters (lin cung)

Storing small files on afilesystem with large clusterswill therefore waste disk space;such wasted disk space is

called slack space. Two formatting types:

Low-level format High-level format

A: Track

B: Sector Track

C: Sector

D: Cluster


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LOW LEVEL FORMATTING

Turns platter from blank slatedividedslate

Defines data areas: creates tracks, seperatesinto sectors, assigns ID numbers to the

sectors.

Done with a specific utility frommanufacturer (BIOS).


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PARTITION

& HIGH LEVEL FORMATTING Partitioning segments diskseparate areas (C &

D drive)

Drive cant be used without high-level formatting High-level formatting (usually thought asformatting) uses FAT (File Allocation Table)

High-level formatting can be done with DOSFORMAT command or 3rdparty utility (CD-

ROM)


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FILE SYSTEMS

FATFAT12

FAT16FAT32

HPFS

NTFS Ext2/Ext3


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FAT

FAT12: old 12-bit file system for floppies & reallysmall drives.

FAT16: used by DOS, WINDOWS95 & WIN98

support 8-letter file name & 3-letter extensionunder DOS & 256 characters under WINDOWS.A partition capacity =< 2GB

FAT32: Allows partitions up to 2,048GB; mostused in todays PCs FAT32 clusters: 4Kreduce wasted space (Original

clusters: 32K)

Slack: The wasted space of a cluster


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HPFS, NTFS, ext2/ext3

HPFS (High Performance File System):used with OS/2 or early versions of NT,

supports 256 characters in a file name. NTFS (Windows NT File System): Used

with Windows NT, 2000 & XP

Ext2/Ext3 (Extended File System Version2-3): Used by Linux


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MANUFACTURERS

Seagate (now owns Maxtor)

Western Digital

Samsung Hitachi

Fujisu (mobile & server)

Toshiba (major manufacturer of 2.5 & 1.8) ExcelStor (small HDD manufacturer)


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COMMON TERMS

Boot sector: a single sector (normally thefirst in the active partition) that contains the

code to boot the operating system. Rpm (rounds/revolutions per minute)

PC hard disk: 7,200 rpm

Laptop hard disk: 5,400 rpmServer hard disk: 15,000 rpm


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REFERENCES

Oxford English for Information Technology, 2ndedition http://computer.howstuffworks.com/hard-disk7.htm http://news.bbc.co.uk/2/hi/technology/6677545.stm

http://www.ranish.com/part/primer.htm#inside http://www.pcguide.com/ref/hdd/op/act-c.html http://en.wikipedia.org/wiki/External_hard_disk_drive http://www.vnexpress.net/GL/Vi-tinh/Hoi-

dap/2007/07/3B9F822A/ http://it.moj.gov.vn/forum/PrintPost.aspx?PostID=373

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Computer Hard Drive