integrated device electronic and scsi

8/7/2019 Integrated Device Electronic and SCSI

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IDE & SCSI



Wirth's Law: Software

gets slower faster thanHardware gets faster!



How IDE Controllers Work

storage is an important part of your system. In fact,

most personal computers have one or more of the

following storage devices:

Floppy drive

Hard drive

CD-ROM drive



Usually, these devices connect to the computer through an Integrated Drive Electronics (IDE) interface.

Essentially, an IDE interface is a standard way for astorage device to connect to a computer. IDE is actually not the true technical name for the interface standard.

The original name, AT Attachment (ATA), signified that the interface was initially developed for the IBM AT computer.



you will learn about the evolution of IDE/ATA, what

the pinouts are and exactly what "slave" and

"master" mean in IDE.



IDE Evolution

IDE was created as a way to standardize the use of

hard drives in computers. The basic concept behind

IDE is that the hard drive and the controller should

be combined.

The controller is a small circuit board with chips that

provide guidance as to exactly how the hard drive

stores and accesses data.



Before IDE, controllers and hard drives were

separate and often proprietary. In other words, a

controller from one manufacturer might not work

with a hard drive from another manufacturer. The distance between the controller and the hard

drive could result in poor signal quality and affect

performance. Obviously, this caused much frustration

for computer users.



Hard drive controller



IBM introduced the AT computer in 1984 with a couple of key innovations.

The slots in the computer for adding cards used a newversion of the Industry Standard Architecture (ISA) bus. The new bus was capable of transmitting information 16bits at a time, compared to 8 bits on the original ISA bus.

IBM also offered a hard drive for the AT that used a

new combined drive/controller. A ribbon cable from the drive/controller combination ran to an ISA card toconnect to the computer, giving birth to the ATAttachment (ATA) interface.



Since almost all IDE drives are ATA-based, the two

terms are used interchangeably.



Controllers, Drives, Host Adapters

Most motherboards come with an IDE interface. This

interface is often referred to as an IDE controller,

which is incorrect. The interface is actually a host

adapter, meaning that it provides a way to connect a complete device to the computer (host). The actual

controller is on a circuit board attached to the hard

drive.



While the IDE interface was originally developed

for connecting hard drives, it has evolved into the

universal interface for connecting internal floppydrives, CD-ROM drives and even some tape backup

drives. Although it is very popular for internal drives,

IDE is rarely used for attaching an external device.



several variations of ATA

ATA-1

The original specification that Compaq included in

the Deskpro 386.

It instituted the use of a master/slave configuration.

Additionally, ATA-1 provides signal timing for direct

memory access (DMA) and programmed

input/output (PIO) functions.



ATA-2 - DMA was fully implemented beginning with

the ATA-2 version.

Standard DMA transfer rates increased from 4.16megabytes per second (MBps) in ATA-1 to as many

as 16.67 MBps.

ATA-2 provides power management



ATA-3 - With the addition of Self-Monitoring

Analysis and Reporting Technology (SMART), IDE

drives were made more reliable. ATA-3 also adds password protection to access

drives, providing a valuable security feature.



ATA-4 Ultra DMA support and the integration of the

AT Attachment Program Interface (ATAPI) standard.

ATAPI provides a common interface for CD-ROM

drives, tape backup drives.

Before ATA-4, ATAPI was a completely separate

standard. With the inclusion of ATAPI, ATA-4immediately improved the removable media support

of ATA.



ATA-5 - The major update in ATA-5 is auto

detection of which cable is used: the 40-conductor

or 80-conductor version. Ultra DMA is increased to 66.67 MB/sec with the

use of the 80-conductor cable.

ATA-5 is also called Ultra ATA/66.



Cable Key

IDE devices use a ribbon cable to connect to each other. Ribbon cables have all of the wires laid flat next to each other instead of bunched or wrapped together in a bundle.

IDE ribbon cables have either 40 or 80 wires. There is aconnector at each end of the cable and another one about two-thirds of the distance from the motherboard connector.

This cable cannot exceed 18 inches (46 cm) in total length (12 inches from first to second connector, and 6 inches from

second to third) to maintain signal integrity. The three connectors are typically different colours and

attach to specific items:



The blue connector attaches to the motherboard.

The black connector attaches to the primary

(master) drive.

The grey connector attaches to the secondary

(slave) drive.



Masters and Slaves

A single IDE interface can support two devices. Most

motherboards come with dual IDE interfaces

(primary and secondary) for up to four IDE devices.

Because the controller is integrated with the drive, there is no overall controller to decide which device

is currently communicating with the computer.



This is not a problem as long as each device is on a

separate interface, but adding support for a second

drive on the same cable took some ingenuity.



To allow for two drives on the same cable, IDE uses aspecial configuration called master and slave. This configuration allows one drive's controller to tell the other drive when it can transfer data to or from the computer. What happens is the slave drive makes arequest to the master drive, which checks to see if it is currently communicating with the computer. If the master drive is idle, it tells the slave drive to go

ahead. If the master drive is communicating with the computer, it tells the slave drive to wait and theninforms it when it can go ahead.



The computer determines if there is a second

(slave) drive attached through the use of Pin 39

on the connector.

Pin 39 carries a special signal, called Drive

Active/Slave Present (DASP), that checks to see if a

slave drive is present.



Although it will work in either position, it is

recommended that the master drive is attached to

the connector at the very end of the IDE ribbon

cable. Then, a jumper on the back of the drive next to the IDE connector must be set in the correct

position to identify the drive as the master drive.



The slave drive must have either the master jumper removed or a special slave jumper set, dependingon the drive. Also, the slave drive is attached to the connector near the middle of the IDE ribbon cable. Each drive's controller board looks at the jumper setting to determine whether it is a slave or amaster. This tells them how to perform. Every drive is

capable of being either slave or master when youreceive it from the manufacturer. If only one driveis installed, it should always be the master drive.



How SCSI Works

A computer is full of busses -- highways that take

information and power from one place to another.

For example, when you plug an MP3 player or

digital camera into your computer, you're probablyusing a universal serial bus (USB) port. But that bus

isn't big enough to support a whole computer, a

server or lots of devices simultaneously.



(Small Computer System Interface) Pronounced

"scuzzy." SCSI is a hardware interface that allows

for the connection of up to 15 peripheral devices to

a single PCI board called a "SCSI host adapter"that plugs into the motherboard.

SCSI allows any two devices to communicate at

one time (host to peripheral, peripheral to

peripheral).



It's a fast bus that can connect lots of devices to a

computer at the same time, including hard drives,

scanners, CD-ROM/RW drives, printers and tape

drives.



Other technologies, like serial-ATA (SATA), have

largely replaced it in new systems, but SCSI is still in

use.



RAID (Redundant Array of

Independent Disks orRedundant Array of

Inexpensive Disks)Telecom Definition



A storage technology that distributes data across a

group of physically separate hard drives configured as

a single logical memory unit.

As RAID stores all data on redundant drives, it provides a considerable level of fault tolerance.

RAID may involve drives on multiple servers in a cluster

connected via a storage area network (SAN).

A simpler and less expensive approach is known as just

a bunch of disks (JBOD), which essentially is a bunch of

disk drivers not configured as a RAID.



(Redundant Array of Independent Disks) A disk subsystem that increases performance or provides fault tolerance or both. RAID uses two or more

hard drives and aRA

ID controller, which isplugged into motherboards that do not have built-in RAID circuits. Today, most motherboards have RAID built in. In the past, RAID was alsoaccomplished by software only, but was much slower. In the late 1980s, the "I" in RAID stood for "inexpensive," but was later changed to"independent."



SCSI is often used to control a redundant array of

independent discs (RAID). Other technologies, like

serial-ATA (SATA), can also be used for this

purpose. Newer SATA drives tend to be faster and cheaper than SCSI drives.



RAID is a series of hard drives treated as one big

drive. These drives can read and write data at the

same time, known as striping. The RAID controller

determines which drive gets which chunk of data. While that drive writes the data, the controller

sends data to or reads it from another drive



SCSI Types



All of these SCSI types are parallel -- bits of data

move through the bus simultaneously rather than one

at a time. The newest type of SCSI, called Serial

Attached SCSI (SAS), uses SCSI commands but transmits data serially. SAS uses a point-to-point

serial connection to move data at 3.0 gigabits per

second, and each SAS port can support up to 128

devices or expanders.



SCSI Explained

SCSI is pronounced "skuzzy". Now that is out of the way, here is the technical explanation. Every computer needs tobe connected with peripheral devices once in a while. Basically, peripheral devices are those devices that are connected externally to the computer. Now where does SCSIfit in over here? SCSI is set of standards that are used tocommunicate with the peripheral devices. These standards are also used while transferring the data between computer and external devices. SCSI is generally used for communicating with hard drives. It is also used for

communicating with other peripheral devices such as USBflash drives, CD ROM, printers and many data storagedevices.



IDE Explained

Integrated Drive Electronics(IDE) has a history of

gradual development. After going through many

technological advancements, it has evolved into

what is today known as PATA. The underlayingstandard for IDE is AT attachment and hence the

name PATA. The name PATA has been the retronym

for IDE since the introduction SATA.



SATA Explained

If you think SATA is any different than SCSI or IDE, well their end result in functionality is pretty much the same. Just as SCSI is different from IDE, SATA also has some of its owncharacteristics. SATA is an acronym for Serial AT attachment. The work on SATA began with an aim of replacing the older IDE technology. The developers of SATA interface were successful in using the same commands that were used for IDE. As explained above, IDE is a parallel technology, while SATA is a serial technology. SATA also has an IDE emulationmode, which means that SATA interface can operate as IDE,

if the computer motherboard is of old technology and does not support advanced host control interface. Basically its the PATA mode.



SCSI vs SATA vs IDE: Reliability

In the context of comparison, SATA is significantly

more reliable than IDE. If the comparison has to

made between SCSI and IDE again SCSI is far more

reliable than IDE. SATA has already left IDE behind, now it is gaining major grounds against SCSI.



SCSI vs SATA vs IDE: Performance

Continuous research on all three interfaces has

increased their performance, but SATA has shown to

be the most promising of all. SATA has greatly

improved its performance in recent years, but SCSIhas not been able to match such increase. SCSI is

still out performing SATA, but it had high

performance to begin with. SCSI still remains on top

of the three interfaces, but the coming versions ofSATA should out perform SCSI.

integrated device electronic and scsi

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