Begin With The BasicsSCSI (pronounced “skuzzy”) stands for Small Computer System Interface. SCSI is the technology that allows you to connect various peripheral devices to your PC. It is available in two flavors: Parallel SCSI and Serial Attached SCSI.

Parallel SCSI has been the standard in connectivity for more than 20 years, and is known for its stability and reliability.

Serial Attached SCSI (SAS) is the newest generation of SCSI, extending its reliability and stability into environments that demand better performance, scalability, and flexibility, with both Serial ATA (SATA) and SAS drives.

Thes of SCSI

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PerformanceFast I/O connectivityMaximum I/O speedSupports these solutions that require high speed and large amounts of data throughput

ConnectivityPoint-to-point connectionMaximum connectivityConnectivity for internal and external peripheralsBackward compatible with older SCSI versions

FlexibilityExtends the benefits of writing to and reading from multiple devices simultaneously to peripheral devicesCan connect to high-capacity Serial ATA (SATA) drives

Parallel SCSI

Yes320MB/sCD recorders, scanners, tape drives, disk drives

No15 devicesYesYes

Yes

No

Serial Attached SCSI

Yes3Gb/sHigh-performanceSAS disk drives, tape drives

Yes128 devicesYesNo

Yes

Yes

Memorize The Benefits

MB/s

300

250

200

150

100

320

MB/

s

300

MB/

s(3

Gb/

s)

A History of SCSI

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Thes of SCSI

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Study Up On Cable Length

Here’s the general rule for determining the maximum usable cable length for each of the current types of SCSI.

TypeSCSI-1Fast SCSIFast Wide SCSIUltra SCSIWide Ultra SCSI

Ultra2 SCSIUltra 160 SCSIUltra 320 SCSISerial Attached SCSI

Cable Length6 meters (19.5 feet)3.0 meters (9.5 feet)3.0 meters (9.5 feet)1.5 meters (4.5 feet)1.5 meters for ≥ 4 devices3 meters for ≤ 3 devices12 meters (39 feet)12 meters (39 feet)12 meters (39 feet)10 meters (30 feet)

Connect with Adaptec SCSIFrom the early days, more than 25 years ago, when Adaptec was a pioneer in SCSI technology, we have been a leading supplier of SCSI controllers. Today, we build this expertise into a wide range of parallel and serial SCSI solutions for all your connectivity needs.

BIOS Basic Input/Output System. A motherboard BIOS controls the basic functions of the computer, such as the keyboard, monitor, etc. With a SCSI card, the BIOS controls the SCSI disk drives and performs the hard disk boot function.

Bus Mastering or Direct Memory Access (DMA) The fastest method of data transfer available for multi-tasking operating systems using parallel SCSI. Data is transferred from SCSI devices to system memory (RAM) via the SCSI card without using the system’s CPU.

Daisy Chain A cable configuration in which internal and external SCSI devices, such as hard drives, CDs, scanners, and tape drives are connected in series to the SCSI card.

I/O. Input/Output Refers to an operation, program, or device that enters data into or extracts data from a computer.

Point to Point The connectivity protocol used in SAS, in which each device has a dedicated connection to the controller. If a device fails, the failure is isolated at that device.

SAS Expander A switch which allows maximum SAS expansion, enabling a single card to connect to 128 devices and multiple hosts to connect to multiple devices.

SCSI Bus An expansion bus used by parallel SCSI devices to send data to and receive data from system memory (RAM) and the CPU.

SCSI ID A unique identification number used for each device.

Seamless Streaming Unique Adaptec technology that optimizes Ultra 320 SCSI performance by minimizing the command overhead and maximizing the speed as multiple commands are transferred in a single connection.

Termination A feature that stops the data signal at the beginning and end of the parallel SCSI bus. The first and last devices on the SCSI bus must be terminated.

SCSI Glossary

Compare the interfacesLearn the Types of SCSI

SCSI Type

SCSI-1

Fast SCSI

Fast Wide SCSI

Ultra SCSI

Wide Ultra SCSI

Ultra2 SCSI

Wide Ultra2 SCSI

Ultra 160 SCSI

Ultra 320 SCSI

Serial Attached SCSI

Speed

5MB/s

10MB/s

20MB/s

20MB/s

40MB/s

40MB/s

80MB/s

160MB/s

320MB/s

3Gb/s

Connector

IDC50, Centronics 50, and DB25

IDC50, Centronics 50, and 50-pin High Density

68-pin High Density

IDC50, 50-pin High Density

68-pin High DensityPrimarily used for hard drive connections

IDC50, 50-pin High Density

68-pin High DensityPrimarily used for hard drive connections

68-pin High DensityPrimarily used for hard drive connections

68-pin High DensityPrimarily used for hard drive connections

x4 and x8 SAS ConnectorsPrimarily used for hard drive and storage device connections

Compatible Disk Drives

SCSI

SCSI

SCSI

SCSI

SCSI

SCSI

SCSI

SCSI

SCSI

SATA, SAS

Bus Width(bits)

8

8

16

8

16

8

16

16

16

N/A