Lecture Notes: SCSI (Small Computer Systems Interface)

Introduction to SCSI

SCSI (pronounced "scuzzy") stands for Small Computer Systems Interface.
It's a standard interface for connecting storage devices, scanners, printers, and other network devices.
Initially designed for daisy-chaining multiple devices to a single computer interface.
Many SCSI standards support up to 16 devices in one chain.

iSCSI: SCSI over IP, used in virtual networks.
Connectivity Options:
- PATA: Parallel connectivity.
- SATA: Serial connectivity.
SCSI supports both parallel and serial connectivity.

Before SATA and USB standards, SCSI connected peripherals like scanners, CD-ROM drives, and tape backups.
Both internal and external SCSI interfaces were used historically.
Daisy Chaining: A single interface could support multiple devices (up to 8 devices with narrow bus, 16 with wide bus).
Intelligent Connectivity: SCSI manages device identification and access over the connection.

Although less popular now, SCSI is still used, especially in virtual systems and some older hardware.
Example: Older motherboards might have a SCSI connector alongside floppy drive and PATA interfaces.
Different SCSI standards and connectors exist, such as the Ultra 3 68-pin connector.

SCSI ID: Each device on a SCSI cable is assigned a unique ID.
Example: Computer might be SCSI ID 0, hard drive SCSI ID 2, CD-ROM SCSI ID 3.
Logical Unit Number (LUN): Identifies individual drives within a larger SCSI ID device like a drive array.
Terminators are used at the end of SCSI cables to enable communication across multiple devices.

SAS: A newer SCSI standard, more simplified and doesn't require manual SCSI ID settings or terminators.
Point-to-Point Connection: Direct connection between the motherboard and the drive, no daisy chaining.
Provides higher throughput and easier implementation in modern systems.
SAS Drives: Similar in appearance to SATA drives but have different connectors.
Example: High-density internal SAS connectors and SAS arrays for multiple drives in a single chassis.

From PATA to SATA and SCSI to SAS: Evolution from parallel to serial communication increased speed and simplified implementation.
SCSI remains a robust protocol standard, with SAS offering modern enhancements in speed and ease of use.

Next Topic: Transition from PATA to SATA and SCSI to SAS.