EIDE or SCSI: Which one should you choose?

EIDE or SCSI: Which one should you choose?

By Zatni Arbi

JAKARTA (JP): Just two months ago I assembled a 120 MHz Pentium system for a client. We put in 16 MB of RAM made by Kingston, a fast Winfast SuperVGA card from Leadtek, and a 540 MB IDE hard disk from Quantum. The motherboard we chose was the one made by Intel, called Advanzed/ZP. We loaded Win-95. The expensive system turned out to be a clunker!

After some retrospection, we realized that the culprit was the old-fashioned IDE hard disk. While a hard disk of this type was adequately fast for a 486-based machine, it sure creates a bottleneck to data flow in a fast Pentium machine. The matter was aggravated because we used Win-95 as its operating system. Win-95 pages to the swap file on the hard disk more often than Windows 3.x because it is more memory-hungry.

So, no matter how screaming fast the CPU is, as long as the data comes from a slower hard disk the machine will run just slightly faster -- if at all any faster -- than a 486DX-100 machine.

IDE vs EIDE

But, which hard disk subsystem should we choose? At the moment, in addition to IDE, we have Enhanced IDE and SCSI. Each of these has different flavors, too. We have fast SCSI, wide SCSI, fast and wide SCSI. The coming generation is Ultra SCSI. So, let's explore them briefly so that we can have some idea of what to look for when buying a high-end Pentium PC.

The history of IDE goes back to the 1987 era, when this hard disk interface standard replaced the slow ST-506 standard used in earlier generations of PCs. As you can easily guess, the only significant competitor for the IDE standard was, and still is, the SCSI standard. But, at that time, the SCSI hard disks cost much more than the IDE ones of the same size.

As hard disk capacity grew, so did users' appetites for faster performance. The original IDE standard had to be modified to enable it to control bigger and faster hard disks. An original IDE drive could offer only up to 528 MB storage space. To break this 528 MB barrier, we now have Enhanced IDE, or EIDE standard, which was the brainchild of the people at Western Digital.

What are the benefits of EIDE? Well, for starters, most new motherboards now come with an on-board EIDE interface. There's no more need to buy a separate EIDE controller card. Most of these built-in EIDE interface can handle four EIDE devises, so that you can have three hard disk and one CD-ROM driver (such as Sony CDU- 55E) without having to buy an additional interface card. It saves one slot on the motherboard.

Other benefits include faster performances than the old IDE and bigger hard disk capacity than IDE (an EIDE hard disk capacity can be over 8 GB large).

SCSI

Still, few motherboards come with a SCSI adapter built-in. Therefore, you will need to spend some money and buy a SCSI adapter card if you opt for the SCSI subsystem. On my own PCs, I use AdvanSys AdvanSCSI cards; they are lightning fast but they fare rather poorly in compatibility. For future expandability, you'd better use Adaptec 2940, which is the favorite among serious computer users nowadays. An Adaptec 2940 card is widely available here in Jakarta for less than Rp 600,000 (PCI).

You may ask whether we need an IDE hard disk if we have a SCSI one? The answer is no. We can use a SCSI drive as the primary, or boot, drive, as long as we assign the device number 0 to it and the machine does not have any IDE drive on it. We can even use a removable storage drive, such as SyQuest, as the boot drive as long as it has been assigned SCSI device number 0.

Now, what are the benefits of SCSI? Well, if you have a SCSI adapter card on your system, you can daisy-chain up to seven SCSI devices to your system. These may include a SCSI CD-ROM drive, a SCSI tape backup, a high-capacity SCSI hard disk, and a scanner. You can even attach a ZIP drive or a SyQuest external drive very easily to your system if you already have a SCSI host adapter (EIDE cannot handle external devices).

Final world

If you multitask a lot -- for instance, you send out faxes while working on CorelDRAW! 6.0 -- you'd be better off using a SCSI hard disk than an EIDE one since Win 95 will be able to multitask more smoothly. From the ground up, SCSI devices are designed to handle multiple data requests simultaneously.

By the way, in case you are really into CD-ROM and you would like to burn your own platter, you will need two SCSI adapters (it is possible to add more than one SCSI adapters to your system). One of the two will control the hard disk where a copy of the contents of the CD-ROM will be created, and the other will control the CD-ROM writer. If you control both devices with one SCSI adapter, you'll be wasting your blank CD-ROMs because conflicts will occur.

The array of nomenclatures of the EIDE and SCSI standards are really daunting. However, we might as well just ignore them. Ultra SCSI will become the mainstream in the near future, and further down the alley we even see the so-called fiber-channel SCSI coming. However, Fast SCSI 2 is more than sufficient for most current desktop PCs. In general, based on the reports I've read, there's no significant performance advantage from either EIDE or SCSI. Either one will be fine for most applications of Windows 95.

But SCSI does have brighter promises for the future. So, whether you choose to stick to Enhanced IDE or not, it seems that any new system you buy will eventually require a SCSI adapter. In fact, I use one on each of my two PCs in my home office.

If you want to keep cost down by delaying the purchase of a SCSI adapter plus a SCSI hard disk, then you should make sure that you buy an EIDE, not just an IDE, a hard disk like the one we put in our so-so Pentium 120 MHz.

An EIDE hard disk will probably cost you just slightly less than a SCSI one for the same storage capacity. That means that the most significant difference between EIDE and SCSI hard disk subsystem is the cost of the SCSI adapter.

Finally, keep in mind, too, that not all SCSI hard disks are the same. In general, the faster the hard disk mechanical spin, the better the performance. One good choice for SCSI drive today is the new Quantum Fireball, which spins at 5400 revolutions per minute (rpm).