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).