SCSI Overview

Definition

• SCSI: Small Computer Systems Interface
• Standard interface for connecting storage devices, scanners, printers, and more.
• Allows daisy-chaining of multiple devices.
• Supports up to 16 devices in a single chain.

History and Evolution

• Established standard with multiple versions over time.
• Original purpose was to connect peripherals and storage devices before SATA and USB.
• Transitioned from parallel to serial communication similar to SATA evolution.

Types of SCSI

• Parallel SCSI: Original form, supports daisy-chaining with multiple connectors.
• Serial Attached SCSI (SAS): Newer form, simplifies connections with point-to-point configuration.
• iSCSI: SCSI over IP, used in virtual networks.

SCSI Connectivity

• Cable and Connectors: Various connector types including Ultra 3 with 68 pins.
• SCSI ID: Each device has a unique ID for differentiation on the same cable.
• Logical Unit Number (LUN): Used to identify individual drives within a large array.
• SCSI Terminator: Used at the end of the cable to manage data flow and prevent signal reflection.

Advantages

• Intelligent connectivity – auto-identifies and manages devices.
• Still used in certain environments, especially virtual systems.

Serial Attached SCSI (SAS)

• No need for terminators or SCSI ID settings.
• Simplified configuration compared to parallel SCSI.
• Offers point-to-point connections improving speed and simplicity.
• Example: SAS drive looks similar to SATA but with slightly different connectors.

Practical Application

• Motherboard Integration: Older motherboards may still have SCSI connectors.
• External Storage Devices: Can daisy-chain via SCSI in/out ports.
• Modern Systems: Use of SAS for enhanced speed and simplified connections.

Future Considerations

• Transition from parallel to serial has increased throughput and simplified implementation.
• SAS provides modern speeds and maintains SCSI protocol benefits.

Conclusion

• SCSI remains relevant in specific applications and continues to evolve with updated standards like SAS.
• Next focus: Transition from PATA to SATA, paralleling SCSI evolution.