integrated device electronic and scsi
TRANSCRIPT
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IDE & SCSI
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Wirth's Law: Software
gets slower faster thanHardware gets faster!
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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
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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.
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you will learn about the evolution of IDE/ATA, what
the pinouts are and exactly what "slave" and
"master" mean in IDE.
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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.
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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.
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Hard drive controller
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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.
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Since almost all IDE drives are ATA-based, the two
terms are used interchangeably.
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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.
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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.
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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.
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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
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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.
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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.
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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.
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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:
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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(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).
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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.
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Other technologies, like serial-ATA (SATA), have
largely replaced it in new systems, but SCSI is still in
use.
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RAID (Redundant Array of
Independent Disks orRedundant Array of
Inexpensive Disks)Telecom Definition
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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.
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(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."
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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.
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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
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SCSI Types
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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.
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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.
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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.
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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.
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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.
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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.