9 - IDE Controllers

8/13/2019 9 - IDE Controllers

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How IDE Controllers Workby Jeff Tyson

The hard drive and circuit board combinationthat typify IDE devices

Usually, these devices connect to the computer through an Integrated Drive Electronics(IDE) interface. Essentially, an IDE interface is a standard ay for a storage device toconnect to a computer. IDE is actually not the true technical name for the interface standard.The original name, AT Attachment(!T!), signified that the interface as initially developedfor the I"# !T computer. In this article, you ill learn about the evolution of IDE$!T!, hatthe pinouts are and e%actly hat &slave& and &master& mean in IDE.

IDE EvolutionIDE as created as a ay to standardi'e the use of hard drives in computers. The basicconcept behind IDE is that the hard drive and the controller should be combined. Thecontroller is a small circuit board ith chips that provide guidance as to e%actly ho the harddrive stores and accesses data. #ost controllers also include some memorythat acts as abuffer to enhance hard drive performance.

"efore IDE, controllers and hard drives ere separate and often proprietary. In other ords,a controller from one manufacturer might not or ith a hard drive from anothermanufacturer. The distance beteen the controller and the hard drive could result in poorsignal uality and affect performance. *bviously, this caused much frustration for computerusers.

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+o matter hat you do ith your computer, storage is an important part of your system. In fact, mostpersonal computershave one or more of the folloing storage devices

-loppy drive ard drive

/D01*# drive
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The birth of the IDE interface led to combining a controller likethis one with a hard drive

I"# introduced the !T computer in 2345 ith a couple of ey innovations.

The slots in the computer for adding cards used a ne version of the Industry

!tandard Architecture(I6!) bus. The ne bus as capable of transmittinginformation 27bitsat a time, compared to 4 bits on the original I6! bus.

I"# also offered a hard drive for the !T that used a ne combined drive$controller. !

ribbon cable from the drive$controller combination ran to an I6! card to connect tothe computer, giving birth to the !T !ttachment (!T!) interface.

In 2347, /ompa introduced IDE drives in their Despro 847. This drive$controllercombination as based on the !T! standard developed by I"#. "efore long, other vendorsbegan offering IDE drives. IDE became the term that covered the entire range of integrated

drive$controller devices. 6ince almost all IDE drives are !T!0based, the to terms are usedinterchangeably.

/ontrollers, Drives, ost !dapters#ost motherboardscome ith an IDE interface. This interface is often referred to as an IDEcontroller, hich is incorrect. The interface is actually a host adapter, meaning that itprovides a ay to connect a complete device to the computer (host). The actual controller ison a circuit board attached to the hard drive. That9s the reason it9s called Integrated DriveElectronics in the first place:

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A close"up of the primary and secondary IDE interfaceson a motherboard

;hile the IDE interface as originally developed for connecting hard drives, it has evolvedinto the universal interface for connecting internal floppy drives, /D01*# drives and evensome tape bacup drives. !lthough it is very popular for internal drives, IDE is rarely used for

attaching an e%ternal device.

There are several variations of !T!, each one adding to the previous standard andmaintaining bacard compatibility.

The standards include

ATA"#0 The original specification that /ompa included in the Despro 847. It

instituted the use of a master$slave configuration. !T!02 as based on a subset ofthe standard I6! 370pin connector that uses either 5< or 55 pin connectors andcables. In the 550pin version, the e%tra four pins are used to supply poer to a drivethat doesn9t have a separate poer connector. !dditionally, !T!02 provides signal

timing for direct memory access(D#!) and programmed input$output (=I*)functions. D#!means that the drive sends information directly to memory, hile =I*means that the computer9s central processing unit(/=U) manages the informationtransfer. !T!02 is more commonly non as IDE.

ATA"$0 D#! as fully implemented beginning ith the !T!0> version. 6tandard

D#! transfer rates increased from 5.27 megabytes per second (#"ps) in !T!02 toas many as 27.7? #"ps. !T!0> provides poer management, =/#/I! cardsupportand removable device support. !T!0> is often called EIDE (Enhanced IDE), -ast

!T! or -ast !T!0>. The total hard drive si'e supported increased to 28?.5

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gigabytes. !T!0> provided standard translation methods for Cylinder Head !ector(/6) for hard drives up to 4.5 gigabytes in si'e. /6 is ho the system determineshere the data is located on a hard drive. The reason for the big discrepancybeteen total hard drive si'e and /6 hard drive support is because of the bit si'esused by the basic input$output system ("I*6) for /6. /6 has a fi%ed length foreach part of the address. @oo at this chart

Cylinder 2A7

!ector 70bit %&'

Bou ill note that the number of sectors is 78 instead of 75. This is because a sector

cannot begin with (ero. Each sector holds A2> bytes. If you multiply 2,5 % >A7 %78 % A2>, you ill get 4,5AA,?27,475 bytes or appro%imately 4.5 gigabytes. +eer"I*6 versions increased the bit si'e for /6, providing support for the full 28?.5

gigabytes. ATA"&0 ;ith the addition of 6elf0#onitoring !nalysis and 1eporting Technology

(6#!1T), IDE drives ere made more reliable. !T!08 also adds passordprotection to access drives, providing a valuable security feature.

ATA")0 =robably the to biggest additions to the standard in this version are Ultra

D#! support and the integration of the AT Attachment *rogram Interface(!T!=I)standard. !T!=I provides a common interface for /D01*# drives, tape bacupdrives and other removable storagedevices. "efore !T!05, !T!=I as a completelyseparate standard. ;ith the inclusion of !T!=I, !T!05 immediately improved theremovable media support of !T!. Ultra D#! increased the D#! transfer rate from

!T!0>9s 27.7? #"ps to 88.88 #"ps. In addition to the e%isting cable that uses 5A 0I*1

5 Data "it 4 >7 round

A Data "it 7 >? I$* /hannel 1eady

7 Data "it 3 >4 6=6B+/ /able 6elect

? Data "it A >3 0D!/ 8

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2< Data "it 22 8> 0I*/6 27

22 Data "it 8 88 !ddress "it 2

2> Data "it 2> 85 0=DI!

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23 round 52 HA olts (@ogic) (*ptional)

>< /able ey (pin missing) 5> HA olts (#otor) (*ptional)

>2 D1F 8 58 round (*ptional)

>> round 55 0Type (*ptional)

+ote that the last four pins are only used by devices that reuire poer through the ribboncable. Typically, such devices are hard drives that are too small (for e%ample, >.A inches) toneed a separate poer supply.

#asters and 6laves! single IDE interface can support to devices. #ost motherboards come ith dual IDEinterfaces(primary and secondary) for up to four IDE devices. "ecause the controller isintegrated ith the drive, there is no overall controller to decide hich device is currentlycommunicating ith the computer. This is not a problem as long as each device is on aseparate interface, but adding support for a second drive on the same cable too someingenuity.

To allo for to drives on the same cable, IDE uses a special configuration called masterand slave. This configuration allos one drive9s controller to tell the other drive hen it cantransfer data to or from the computer. ;hat happens is the slave drive maes a reuest tothe master drive, hich checs to see if it is currently communicating ith the computer. Ifthe master drive is idle, it tells the slave drive to go ahead. If the master drive iscommunicating ith the computer, it tells the slave drive to ait and then informs it hen itcan go ahead.

The computer determines if there is a second (slave) drive attached through the use of =in83 on the connector. =in 83 carries a special signal, called Drive Active,!lave *resent(D!6=), that checs to see if a slave drive is present.

!lthough it ill or in either position, it is recommended that the master drive is attached tothe connector at the very end of the IDE ribbon cable. Then, a Cumper on the bac of thedrive ne%t to the IDE connector must be set in the correct position to identify the drive as themaster drive. The slave drive must have either the master Cumper removed or a special slave

Cumper set, depending on the drive. !lso, the slave drive is attached to the connector nearthe middle of the IDE ribbon cable. Each drive9s controller board loos at the Cumper settingto determine hether it is a slave or a master. This tells them ho to perform. Every drive iscapable of being either slave or master hen you receive it from the manufacturer. If onlyone drive is installed, it should alays be the master drive.

#any drives feature an option called Cable !elect(/6). ;ith the correct type of IDE ribboncable, these drives can be auto configured as master or slave. /6 ors lie this ! Cumper

on each drive is set to the /6 option. The cable itself is Cust lie a normal IDE cable e%ceptfor one difference 00 =in >4 only connects to the master drive connector. ;hen yourcomputer is poered up, the IDE interface sends a signal along the ire for =in >4. *nly thedrive attached to the master connector receives the signal. That drive then configures itselfas the master drive. 6ince the other drive received no signal, it defaults to slave mode.

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9 - IDE Controllers