PC Hardware

Lesson Summary

The following points summarize the main elements of this lesson:

  • Originally, hard disk drives were limited to storage capacity that did not exceed 528 MB.

  • Using new technology, the old hard disk drive limit has been exceeded.

  • Modern computers allow up to four IDE drives to be installed on built-in controllers.

  • Properly setting PIO will enhance the performance of a drive.

  • 32-bit disk access provides a major speed improvement for disk drives.

Lesson 3: SCSI Drives

The Small Computer System Interface (SCSI) has become the mass-storage device of choice for large network installations. SCSI was first introduced in Tutorial 8, Lesson 2: Hard Disk Drives, and has many advantages over standard IDE and EIDE drives. SCSI is the favored drive for high-end workstations, network and Internet servers, and the Macintosh line of personal computers. In many installations, the advantages far outweigh the slight extra effort in configuration. In this lesson, we explore the advantages and uses of a SCSI system.

After this lesson, you will be able to:
  • Define the advantages and disadvantages of a SCSI system.

  • Determine whether a SCSI system is best for your client.

  • Set up a SCSI system.

Estimated lesson time: 30 minutes

SCSI was introduced in 1979 as a high-performance interface, allowing connection of both internal and external devices. Because it runs on virtually any operating system, it was adopted by the ANSI Standards Committee and is now an open standard in its third generation.

At its core, SCSI is a simple design. A single card, the host adapter, (or a chip set on the motherboard) connects up to 15 devices. These devices can be attached inside or outside the PC using standard cables and connectors. SCSI is the only interface that can connect such a wide variety of devices. Communication between the devices and the host adapter is done without involving the CPU or the system bus until data must be passed to one or the other.

This design frees expansion slots and reduces the number of interrupts and memory addresses needed, while cutting down the number of drivers required. Less-robust solutions, such as IDE and EIDE, are little more than switching stations, relying on the PC's CPU to manage the data bus. SCSI host adapters are true subsystems with advanced commands that can order and route data to improve performance.