Small Computer System Interface (SCSI) pronounced as skuzzy. The SCSI system consists of the SCSI controller that communicates with the system. The SCSI cables are used to connect the SCSI drives to the SCSI controller and the SCSI devices. SCSI interfaces are mainly used to connect HDD, tape storage devices, printers and scanners. SCSI drives are more costly and faster as compare to IDE drives. SCSI enables fast communication between the system and the device.

1. SCSI DRIVES

2. Introduction
 Small Computer System Interface (SCSI) pronounced
as skuzzy.
 The SCSI system consists of the SCSI controller that
communicates with the system.
 The SCSI cables are used to connect the SCSI drives to
the SCSI controller and the SCSI devices.
 SCSI interfaces are mainly used to connect HDD, tape
storage devices, printers and scanners.
 SCSI drives are more costly and faster as compare to
IDE drives.
 SCSI enables fast communication between the system
and the device.

3. Advantages of SCSI
 The SCSI devices have data transmission speeds that can
reach about 320 MB per second between the system and
device.
 It allows you to attach up to a single SCSI port.
 The SCSI controller on the SCSI device boots the signals and
enables the devices to be connected at a distance of about
25 meters from the system.
 The SCSI devices reduce the processing load on the
microprocessor, as they have a micro – controller built into
the device.
 The communication problems between the system and SCSI
device due to data signals reflecting back when cables are
left open are reduced, as the ends of the SCSI have
terminators.

4. Types of SCSI Interface
 SCSI – 1.
 SCSI – 2.
 SCSI – 3.

5. SCSI variations
 Narrow SCSI.
 Wide SCSI.
 Fast SCSI.
 Fast wide SCSI.
 Wide Ultra SCSI.

6. SCSI variations
variation Bandwidt
h
Bus
speed
MHz
DTR
MBs
Type of
SCSI
Connector used
SCSI 8 5 5 SCSI 1 50 pin connector.
Fast SCSI 8 10 20 SCSI 2 50 pin internal or
external
connector.
Fast wide
SCSI
16 10 20 SCSI 2 Wide 68 pin
connector (I/E)
Wide ultra 1
SCSI
16 20 40 SCSI 3 Wide 68 pin
connector.
Wide ultra 2
SCSI
16 16 4080 SCSI 3 Wide 68 pin,
VHDCI 68pin
Wide ultra 3
SCSI
20 16 40 SCSI 3 Wide 68 pin,
VHDCI 68 pin
Wide ultra 3 16 40 320 SCSI 3 68 pin connector

7. SCSI drive speeds
 The speed of a hard disk
is depends on the speed
of the platters.
 Faster the platter rotates,
faster the data will be
written and accessed
from the hard disk.
 SCSI drives are available
at speeds of 10,000 RPM
and 15000 RPM.

8. SCSI drives
 Universal HDD make it easier
to upgrade the server hard
disk drive.
 It is hot swappable.
 It is based on ultra320 , ultra
3 or ultra 2 technology.
 It supports Self Monitoring
Analysis and Reporting
Technology (SMART).
 SMART feature monitors the
working of the HDD and
warns about any potential
damage to the hard disk.
 SAS is a serial
communication protocol
for computer storage
devices.
 It is backward
compatible with SATA
technology.
 It is designed for
corporate and
enterprise markets.
 SAS uses serial
communication instead
of parallel
communication.
Universal Hard Disk Drive Serial Attached SCSI (SAS)

9. Types of SCSI Bus signals
 SCSI bus signal specifies the method that is
used by the SCSI devices to communicate
with each other.
Single – Ended (SE)
Low – Voltage Differential (LVD)
High – Voltage Differential (HVD)
Low – Voltage Differential / Single – Ended Multi – mode
(LVD/SE)

10. Working with SCSI connectors
 SCSI connectors enables the user to connect
the SCSI cable to the SCSI adapter or the
SCSI device.
 We have two kinds of SCSI connectors.
 1. Internal SCSI connectors.
 2. External SCSI connectors.

11. Internal connectors
Number of pins Description
50 pin connector Used to connect SCSI 1 and
SCSI 2 internal devices.
68 pin connector Used to connect SCSI 3 ultra
wide and LVD internal devices.

12. External connectors
Number of pins Description
50 pin connector Used to connect 8 – bit SCSI for
external devices.
25 pin connector 8 – bit connector used on Apple
computers. It looks similar to parallel
port.
68 pin connector Used to connect 16 – bit and 32 – bit
SCSI 2 devices.
80 pin connector It is also known as Alternative 4. used
to attach hot swappable SCSI 3
devices.

13. SCSI cables
Internal SCSI cables External SCSI cables
SCSI cables are used to connect the system, the SCSI controller and the
SCSI devices.

14. Termination Requirement
 The SCSI terminator is
used to terminate the
SCSI chain of devices.
 Terminator enables that
the signal transmitted
by last device does not
reflect backwards into
the SCSI chain.
 Data does not disturb
by last device signal.
 The SCSI devices uses
Active and passive
terminators.

15. Working with SCSI Drives
 SCSI devices transfer
data between the
device and the system
at great speeds.
 SCSI enables to
connect multiple hard
disks together to form a
single unit by
implementing RAID
technology.
 We can connect an
other device to the
SCSI chain with out
switching off the
system.

16. RAID
 Redundant Array of Inexpensive Disks.
 It is a technology that uses a collection of hard
disks to share and replicate data.
 In this technology OS recognizes multiple hard
disks as a single hard disk.
 It keeps your data safe by enabling you to
recover data lost due to hard disk crashing.

17. Levels of RAID
 RAID Level 0.
 RAID Level 1.
 RAID Level 2.
 RAID Level 3.
 RAID Level 4.
 RAID Level 5.
 RAID Level 6.
 RAID Level 0 + 1.
 RAID Level 10.
 RAID Level 53.
 Linear RAID.

18. Hot swappable devices
 Hot swappable
devices enable you
to connect and
disconnect devices
to the system with
out shutting down or
restarting the
system.