Overview
This lecture explains the SCSI (Small Computer Systems Interface) standard, its evolution, configurations, and its role in connecting multiple devices, with a focus on both traditional and modern implementations like SAS.
SCSI Basics
- SCSI (pronounced "scuzzy") stands for Small Computer Systems Interface.
- It is a standard interface to connect storage devices, scanners, printers, and other peripherals.
- SCSI allows multiple devices (up to 16) to connect via daisy chaining on a single interface.
- Different SCSI standards employ different connectors and cables.
- SCSI supports both parallel and serial connectivity.
SCSI Device Management
- Each device on a SCSI chain is assigned a unique SCSI ID for identification.
- SCSI chains require terminators at the end to maintain communication integrity.
- Logical Unit Numbers (LUNs) are used to identify individual drives within a device like a drive array.
- SCSI manages device detection and access automatically.
Parallel SCSI vs. Serial SCSI (SAS)
- Traditional SCSI uses parallel communication and requires manual SCSI ID setup and terminators.
- Serial Attached SCSI (SAS) uses point-to-point serial communication, removing the need for daisy chaining and terminators.
- SAS simplifies configuration and increases data transfer speeds.
- SAS connectors and cables are different from older SCSI and SATA connectors.
Usage and Evolution
- SCSI was widely used before SATA and USB, especially for connecting scanners, CD-ROMs, and backup tape systems.
- SCSI is still found in some systems and is used in virtual environments.
- Ultra 3 SCSI uses a 68-pin connector and cable to support multiple devices.
- SCSI standards have evolved to support modern storage needs and higher speeds.
Key Terms & Definitions
- SCSI (Small Computer Systems Interface) — A standard for connecting multiple devices to a computer.
- Daisy Chaining — Connecting multiple devices in series on a single cable.
- SCSI ID — A unique identifier assigned to each device on a SCSI chain.
- Terminator — A device placed at the end of a SCSI chain to enable proper communication.
- LUN (Logical Unit Number) — Identifies individual devices within a larger SCSI device.
- SAS (Serial Attached SCSI) — Modern serial version of SCSI, simplifying connections and increasing speed.
Action Items / Next Steps
- Review the differences between SCSI, PATA, and SATA.
- Prepare for the next lecture on the evolution from parallel to serial communication in storage interfaces.