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 SCSI Disk
EIDE vs SCSI - Why purchase SCSI by P.A.P. Den Haan
Why use SCSI by Michael Neuffer
How to install SCSI Hard Drive by Rad
Determining Single-Ended SCSI or Differential (HVD) SCSI Interface by Paralan Corporation
SCSI - A game with many rules and no rulebook by Gary Field
SCSI Interface by David Risley
The Ten Commandments of SCSI by Gary Field
The Complete Guide to SCSI for the Powerbook by Charled Moore


Why Should you use SCSI?

The article published below is part of a complete article from Michael Neuffer.


With the SCSI interface making such great strides in features, performance and user acceptance, the proponents of the IDE have proposed several enhancements to maintain its viability as an acceptable architecture. The resultant specification is called "Enhanced IDE" (EIDE).


IDE was designed as a low-cost, easy to use interface. Although EIDE has broken the original IDE 528 MB limitation, EIDE transfer rates are still limited to between 9 and 16 MB/s and can only support 4 devices. These devices can only be two hard disk drives, a CD-ROM and a tape drive. Conversely, SCSI is designed for optimum performance and flexibility. Wide Fast SCSI-2 subsystems are capable of transferring data at up to 20 MB/s by utilizing an intelligent SCSI adapter. Disk throughput has always been important in high-end, multi-user systems but until recently has not been an issue with single-user PCs. With the availability of a new generation of operating systems like Linux, *BSD* and other multi-tasking systems and the popularity of software using the CD-ROM, the task of keeping up with the data requirements of these applications has become more challenging. Faster SCSI drives coupled with bus mastering SCSI adapters have begun to look more attractive to users of EIDE drives.


Other advantages of SCSI over EIDE include its ability to process multiple overlapped commands, support for command queuing and support for scatter/gather data transfers. These features combine to optimize and maximize throughput. Since EIDE is still tied to the old WD1003 (ST506) interface, overlapped I/O and command queuing functions cannot be executed and only single task operations are possible.


The performance disadvantages of EIDE, although not so apparent under DOS, still severely limit the performance of multi-tasking operating systems such as Linux, FreeBSD, SCO, OS/2, NetWare and Windows NT. These operating systems benefit significantly from SCSI's ability to perform overlapped I/O and command queuing.


Unlike EIDE, SCSI supports devices connected to your computer externally. With EIDE, all devices that you connect must reside inside the computer box. This can present some obvious configuration and capability limitations. SCSI also offers parity-based error checking to maximize the probability of error-free data transmission. Additionally, the choice of EIDE devices is limited currently to hard disk drives, CD-ROMs and tape drives, while SCSI devices include hard disk drives, CD-ROMs, WORMs, Optical devices, scanners, tape drives, and many others.


In consideration of SCSI's feature and performance advantages over EIDE, it is the view of industry analysts today that EIDE will continue to be dominant on the low-end, price-sensitive DOS-based PCs, while SCSI will be the peripheral interface of choice for all other platforms, particularly those that are sensitive to performance issues, or any multi-user system.