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1
SCSISCSI
2
SCSI Hard Drives
3
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
7
Internal SCSI Interface Cable
To Host Adapter To SCSI Drives
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Internal SCSI Interface Cable
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MotherboardSCSI Drives
SCSI Host Adapter
Terminators
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MotherboardSCSI Drives
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
12
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
Bus WidthBus Width 16-bit16-bit Data Transfer RateData Transfer Rate 80 MB/s80 MB/s Devices supportedDevices supported 1616
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SPI-3Ultra3 SCSI or Ultra-160 SCSI
Bus WidthBus Width 16-bit16-bit Data Transfer RateData Transfer Rate 160 MB/s160 MB/s Devices supportedDevices supported 1616
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SPI-4Ultra-320 SCSI
Bus WidthBus Width 16-bit16-bit Data Transfer RateData Transfer Rate 320 MB/s320 MB/s Devices supportedDevices supported 1616
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SPI-5Ultra-640 SCSI
Bus WidthBus Width 16-bit16-bit Data Transfer RateData Transfer Rate 640 MB/s640 MB/s Devices supportedDevices supported 1616
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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.
TerminatorTerminator
SCSIHostAdapter
76543210
34
DisabledTerminator
TerminatorTerminator
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
68
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
70
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
71
Differential Signaling
0 V
+ V
0 V
- V
72
Differential signaling is less prone to noise problems.
0 V
+ V
Signal
Noise
EMI
0 V
- V
73
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.