1 scsi. 2 scsi hard drives 3 scsi drives are faster. scsi drives are faster. more expensive. more...

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SCSISCSI

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SCSI Hard Drives

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SCSI Hard Drives

SCSI drives are faster.SCSI drives are faster. More expensive.More expensive. Require a separate host adapter.Require a separate host adapter. Connect in a daisy-chain.Connect in a daisy-chain. Allows multiple drives from a single host Allows multiple drives from a single host

adapter using a single PCI bus slot and a adapter using a single PCI bus slot and a single IRQ.single IRQ.

Allows multiple commands.Allows multiple commands.

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Motherboard

Slave

Master

ATA Drives

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Motherboard

PrimarySlave

SecondaryMaster

ATA Drives

SecondarySlave

PrimaryMaster

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MotherboardSCSI Drives

SCSI Host Adapter

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Internal SCSI Interface Cable

To Host Adapter To SCSI Drives

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Internal SCSI Interface Cable

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SCSI Host Adapter

Terminators

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SCSI Host Adapter

SCSIController

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Connecting External SCSI Devices

IN IN INOUT OUT OUT

From SCSI Host Adapter

TerminatorS

CS

I D

evic

e

SC

SI

Dev

ice

SC

SI

Dev

ice

SCSI Connectors

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IN OUT

SC

SI

Dev

ice

Adding a SCSI Device

NewDevice

IN IN INOUT OUT OUT

From SCSI Host Adapter

TerminatorS

CS

I D

evic

e

SC

SI

Dev

ice

SC

SI

Dev

ice

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SCSI Host Adapter

External

Internal

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Two Internal and Two External SCSI Peripherals

Host Adapter

Internal SCSI

Peripheral#1

External SCSI

Peripheral #1

Internal SCSIPeripheral #2

External SCSIPeripheral # 2

TerminatorTerminator

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SCSI-1

Bus WidthBus Width 8-bits (1 byte)8-bits (1 byte) Data Transfer RateData Transfer Rate 5 MB/s5 MB/s Devices supportedDevices supported 88

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SCSI-1Terminator

Terminator

HostAdapter SCSI Peripheral Devices

01234567

SCSI Cables

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SCSI-2

Fast SCSIFast SCSI Fast Wide SCSIFast Wide SCSI

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Fast SCSI

Bus WidthBus Width 8-bits (1 byte) 8-bits (1 byte) Data Transfer RateData Transfer Rate 10 MB/s 10 MB/s Devices supportedDevices supported 8 8

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Fast Wide SCSI

Bus WidthBus Width 16-bit (2 bytes)16-bit (2 bytes) Data Transfer RateData Transfer Rate 20 MB/s20 MB/s Devices supportedDevices supported 1616

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SCSI-3

SPI-1SPI-1 Ultra and Wide Ultra Ultra and Wide Ultra SPI-2SPI-2 Ultra2 and Wide Ultra2Ultra2 and Wide Ultra2 SPI-3SPI-3 Ultra3 or Ultra 160Ultra3 or Ultra 160 SPI-4SPI-4 Ultra 320Ultra 320 SPI-5SPI-5 Ultra 640Ultra 640

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SPI-1

Ultra SCSI (Sometimes called Narrow Ultra Ultra SCSI (Sometimes called Narrow Ultra SCSI or Fast-20 SCSI)SCSI or Fast-20 SCSI)

Wide Ultra SCSIWide Ultra SCSI

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Ultra SCSI

Bus WidthBus Width 8-bit 8-bit Data Transfer RateData Transfer Rate 20 MB/s 20 MB/s Devices supportedDevices supported 8 8

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Wide Ultra SCSI

Bus WidthBus Width 16-bit16-bit Data Transfer RateData Transfer Rate 40 MB/s 40 MB/s Devices supportedDevices supported 16 16

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SPI-2

Ultra2 SCSI (Sometimes called Fast-40 Ultra2 SCSI (Sometimes called Fast-40 SCSI or Ultra-40 SCSI)SCSI or Ultra-40 SCSI)

Wide Ultra2 SCSI (Sometimes called Wide Ultra2 SCSI (Sometimes called Ultra-80Ultra-80

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Ultra2 SCSI

Bus WidthBus Width 8-bit8-bit Data Transfer RateData Transfer Rate 40 MB/s40 MB/s Devices supportedDevices supported 88

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Wide Ultra2 SCSI


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SPI-3Ultra3 SCSI or Ultra-160 SCSI


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SPI-4Ultra-320 SCSI


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SPI-5Ultra-640 SCSI


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Data Transfer Rates(Megabytes per

second)

Tim

e

SCSI

FastSCSI

Ultra2SCSI

Wide Ultra2 SCSI

Ultra160SCSI

Wide Ultra SCSI

5 10 20 40 80 160

Ultra320SCSI

Ultra640SCSI

320 640

UltraSCSI

FastWide SCSI

31Data Transfer Rates

Tim

e

SCSI-1

FastSCSI

Ultra2SCSI

Wide Ultra2 SCSI

Ultra160SCSI

Wide Ultra SCSI

5MB 10MB 20MB 40MB 80MB 160MB

Ultra320SCSI

Ultra640SCSI

320MB 640MB

UltraSCSI

FastWide SCSI SCSI-2

SCSI-3SPI-1

SPI-2

SPI-3

SPI-4

SPI-5

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Narrow SCSI is 8-bits wide and Narrow SCSI is 8-bits wide and accommodates 8 devices.accommodates 8 devices.

Wide SCSI is 16-bits wide and Wide SCSI is 16-bits wide and accommodates 16 devices. accommodates 16 devices.

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One of the devices is always the SCSI host adaptor.


SCSIHostAdapter

76543210

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DisabledTerminator


SCSIHostAdapter

765430 21

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Passive SCSI Terminators

220-OhmResistor

330-OhmResistor

TERMPWR

SCSI Bus Line

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Active SCSI Terminator

Voltage Regulator

110-OhmResistor

TERMPWR SCSI Bus Line

2.8V

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Forced Perfect Termination (FPT)

A variation of active termination.A variation of active termination. Includes clamping diodes.Includes clamping diodes. Eliminates signal undershoot and overshoot.Eliminates signal undershoot and overshoot. Contributes to longer cable lengths.Contributes to longer cable lengths.

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SCSI Addressing Scheme or SCSI IDs

8 devices numbered 0 through 78 devices numbered 0 through 7 16 devices numbered 0 through 1516 devices numbered 0 through 15

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SCSI Priority

A kind of “pecking order” to determine A kind of “pecking order” to determine which device gets first shot at using the which device gets first shot at using the SCSI bus. SCSI bus.

Determined by the SCSI ID.Determined by the SCSI ID.

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The SCSI ID determines the priority of the SCSI device.

7 06 5 4 3 2 1

HighestPriority

LowestPriority

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SCSI ID determines priorityTerminator

Terminator

HostAdapter SCSI Devices

01234567

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Customary SCSI IDs

SCSI Host AdapterSCSI Host Adapter ID 7ID 7 Primary Hard DrivePrimary Hard Drive ID 0ID 0

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SCSI Priority

7 06 5 4 3 2 1

Highest Lowest

7 06 5 4 3 2 1

Highest

15 814 13 12 11 10 9

Lowest

Narrow SCSI

Wide SCSI

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SCSI Bus Arbitration

Device waits for bus to become free.Device waits for bus to become free. Device signals its intention to use the bus, Device signals its intention to use the bus,

indicating its address.indicating its address. If a second device attempts to use the bus at If a second device attempts to use the bus at

the same time, the device with the higher the same time, the device with the higher priority wins.priority wins.

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Setting the SCSI ID

Each SCSI device must have a unique ID.Each SCSI device must have a unique ID. The SCSI ID is set when a new SCSI device The SCSI ID is set when a new SCSI device

is installed.is installed. The SCSI Host Adapter should be given The SCSI Host Adapter should be given

SCSI ID 7. SCSI ID 7. May be set by hardware or in software.May be set by hardware or in software.

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Setting the SCSI ID

Jumpers Slide Switches

0 1

3

2

7

5

6

4

Rotary Switch

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Setting the SCSI ID with Jumpers

0 1

7654

32

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IDE

SCSI

WideSCSI

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Logical Unit Number (LUN)

A sub-level addressing scheme.A sub-level addressing scheme. Each SCSI ID can have up to 8 LUN Each SCSI ID can have up to 8 LUN

addresses.addresses. Narrow SCSI allows 7 SCSI IDs times 8 Narrow SCSI allows 7 SCSI IDs times 8

LUN addresses for 56 attached devices.LUN addresses for 56 attached devices. Wide SCSI allows 15 SCSI IDs times 8 Wide SCSI allows 15 SCSI IDs times 8

LUN addresses for 120 attached devices.LUN addresses for 120 attached devices.

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SCSI IDs and LUNs

SCSI ID 0

SCSI ID 1

SCSI ID 2

LUN0

LUN1

LUN2

LUN3

LUN0

LUN1

LUN2

LUN3

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Centronics 50-pin SCSI Connector

2 Rows of 25 Pins

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Centronics 50-pin SCSI Connector

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DB-25 SCSI Connector

1

1

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50-pin High-density SCSI Connector

Latch Latch

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50-pin High-density vs. 50-pin Centronics

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68-pin, High-density SCSI Connector

(HD68)

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68-pin SCSI Connector used on an Internal Ribbon Cable

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68-pin, Very High Density Micro Centronics Connector

(VHDCI68)

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80-pin SingleConnector Attachment

(SCA80)

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50-pin High Density

68-pin High Density

80-pin SCA

50-pin Centronics

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SCSI cable adapter

68-Pin Connector

50-Pin Connector

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01234567

Using the SCSI cable adapter

8-bit Data16-bit Data

68-pin to 50-pinAdapter

16-bitDevices

8-bitDevices

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68-pinCable

50-pin Cable68-pinCable

16-bitData8-bit Data

68/50Adapter

50/68Adapter

HostAdapter

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Mixing Ultra-2 and Ultra-3 SCSI Drives

Ultra-2

Ultra-3

HostAdapter

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SCSI Signaling

Single-ended (SE)Single-ended (SE) Low Voltage Differential (LVD)Low Voltage Differential (LVD) High Voltage Differential (HVD)High Voltage Differential (HVD) Low Voltage Differential/ Single-ended Low Voltage Differential/ Single-ended

Multimode (LVD/SE)Multimode (LVD/SE)

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Single-ended (SE) Signaling

Used by “standard” or normal SCSIUsed by “standard” or normal SCSI Low costLow cost Low performanceLow performance Prone to noise Prone to noise Also called “unbalanced” signalingAlso called “unbalanced” signaling

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Single-ended (SE) Signaling

0 V

+ V

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Single-ended (SE) signaling is prone to noise problems.

0 V

+ V

Signal

Noise

EMI

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6 Meters(About 20 feet)

Single-ended (SE) signaling is limited to a maximum bus

length of 6 meters.

01234567

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Single-ended SCSI vs. Maximum Bus Length

SCSISCSI

TechnologyTechnology Transfer RateTransfer Rate

Max. BusMax. Bus

Length (Meters)Length (Meters)

StandardStandard 5 Mbps5 Mbps 66

WideWide 10 Mbps10 Mbps 66

FastFast 10 Mbps10 Mbps 33

Fast/WideFast/Wide 20 Mbps20 Mbps 33

UltraUltra 20 Mbps20 Mbps 3 or 1.53 or 1.5

Ultra/WideUltra/Wide 40 Mbps40 Mbps 3 or 1.53 or 1.5

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Differential Signaling

0 V

+ V

0 V

- V

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Differential signaling is less prone to noise problems.

0 V

+ V

Signal

Noise

EMI

0 V

- V

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High-voltage Differential (HVD)

Low-voltage Differential (LVD)

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The Problems with High-Voltage Differential (HVD)

High-voltage circuits cost more than low-High-voltage circuits cost more than low-voltage circuits. voltage circuits.

Not compatible with single-ended and Not compatible with single-ended and LVD devices.LVD devices.

Will damage single-ended devices or LVD Will damage single-ended devices or LVD devices on the same bus. devices on the same bus.

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Low-voltage Differential (LVD)

Its differential signaling technique allows Its differential signaling technique allows bus lengths up to 12 meters. bus lengths up to 12 meters.

Requires an LVD terminator that is different Requires an LVD terminator that is different from the standard SCSI terminator.from the standard SCSI terminator.

It uses voltages that are compatible with It uses voltages that are compatible with single-ended SCSI devices.single-ended SCSI devices.

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Low-voltage Differential/ Single-ended (LVD/SE) Multimode

Can communicate with SE devices Can communicate with SE devices If one or more SE device is attached, the If one or more SE device is attached, the

bus length restrictions are those of the SE bus length restrictions are those of the SE device, not the 12 meters of LVD devices device, not the 12 meters of LVD devices

Requires the LVD terminator to work in Requires the LVD terminator to work in the LVD mode. the LVD mode.

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SCSI Symbol Icons

SCSI SE SCSI LVD

SCSIDIFF(HVD) SCSI LVD/SE

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The SCSI icons are important because:

They tell you if the device will work with They tell you if the device will work with your system by indicating the signal type.your system by indicating the signal type.

Putting a high-voltage differential (HVD) Putting a high-voltage differential (HVD) device in a bus with a single ended (SE) or device in a bus with a single ended (SE) or low-voltage differential (LVD) device will low-voltage differential (LVD) device will cause damage.cause damage.

1 scsi. 2 scsi hard drives 3 scsi drives are faster. scsi drives are faster. more expensive. more...

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