Sections Offered In This Course...

The Basics Your PC's hard disk drive holds all information that you "save" as well as all applications. Any time you load a program or save a file, it is given an address on your hard drive and stored for later retrieval. The hard drive differs from the main memory, or RAM in that the RAM holds information only temporarily. When you turn off your PC, the information being held in RAM are lost, unless saved to the hard drive.

The hard drive is the only component that relies on moving parts, and thereby it can slow the entire system. There are many recent improvements in hard drive technology that have made hard drives faster. This performance increase can be seen in booting your PC, saving and retrieving information, processing information and more.

In our opinion, the most important coonsideration for hard drive is its reliability. Early drives were prone to too-frequent crashes, which would make them inaccessible, and the data on them was lost. Today's hard drives are far more reliable, yet not completely infallible.

Hard Drive Glossary.
The Individual Parts And What They Do.
An average hard drive may be made up of one or many hard disks. These disks are referred to as "Platters." Normally, up to four platters are used in the average hard drive. The platters are coated with a special magnetic material on both sides. The platters are stacked together on a spindle, and they all move together as data is stored and retrieved.

Information is accessed by the electromagnetic read/write heads. These heads write, or record magnetic patterns onto the platters when you save data, then read the patterns from the platters when you retrieve data. Data written to a hard disk can be erased (when you delete files or applications) and rewritten.

Information is highly organized as it is written onto the hard disk, with each platter in the hard drive divided into "tracks" and "sectors." The tracks are circular rings, ass illustrated below. Today's hard drives may include tens of thousands of tracks on each platter. Each circular track is the divided into sectors, each of which can hold a specific amout of data, measures in bytes. Groups of sectors are known as clusters.

Performance is increased in hard drive technology as more tracks and sectors can be squeezed onto the disk. Here's the equation: the more sectors there are per track, the more information the drive can read in a SINGLE ROTATION of the platter on the spindle, which means more can be written or retrieved in a shorter period of time. The result is better performance. You'll spend less time waiting for data is the hard drive gathers it faster.

While the platters are highly sophisticated, and the other components
are comprised of advanced technology, it is the read/write heads that are the most expensive part of the hard drive. They are designed and manufactured to incredible specifications. Here's how they work: When the read/write heads are not active, they are "parked" in the hard drive's landing zone, which is a portion of the platter that contains no data. When a command is received from the controller, the read/write heads move to the area of the platter that is populated with data. The read/write heads never actually touch the platter. When the platter begins to spin (at ultra-high rates, some up to 7200 rpm), a cushion of air lifts the read/write heads to just a few millionths af an inch above the platter as it moves. Undestandably, hard disks must remain free any any foreign particles, which would disrupt this air flow and ultimately case the disk to crash, and damage data. Hard drives are sealed to prevent contamination.

The other critical component of a hard drive is the cache buffer, which is a "holding area" made up of memory. When you write to your hard disk, data is transferred from the motherboard to the hard drive where it is deposited into the cache buffer. From the cache buffer, the data is transferred to the platters, where it is written onto the tracks. When information is being read from the disk, the data is transferred from the platters to the cache buffer, then to the motherboard. The cache buffer, in effect, is the pick-up and delivery point for data moving to and from the hard drive. Data that has been recently accessed from the hard drive can be instantly moved from cache memory to the motherboard, without re-accessing the hard drive.

Most moden drives have cache buffers of 2MB, while some less expensive drives have just 1MB.

Let's say you're working on a Microsoft Word document called "Year-End Sales Goals" (remember, as you work, the document is temporarily stored in the PC's main memory). When you complete the document and hit "save," this is what happens next...

1. Microsoft Word sends a command to the operating system (Windows 98 or Windows Me, for example) to store your document in the hard drive.

2. Your document (still in main memory on the motherboard) is moved to the hard drive interface, and transferred to the hard drive's cache buffer.

3. When the document arrives at the cache buffer, the hard drive controller is alerted of its arrival.

4. The hard drive controller is instructed by the operating system to "save" the document to the appropriate address.

5. Upon receiving instructions from the controller, the read/write heads move into position over the appropriate track on the platter and wait for the correct sector to pass under it. When the sector is in position under the read/write heads, one of the read/write heads begins to record the document onto the platter.

6. You have successfuly saved the document to the hard drive.

This simple explanation occurs when you have a relatively small file. However, if you're saving a large graphic file, it may not fit into one sector. If the next sector is empty, the drive will simply continue to write the document into as many sectors as needed. If the entire track fills up, with more information left to be written, the drive will switch heads. Since the heads all move in unison, all the other heads are positioned over the same track on their respective platter surfaces. It is much faster to use an alternate head to record the remaining data than to reposition the heads over a new track. This sequential group of tracks is known as a cylinder, referencing the fact that they are on top of each other, rather than side by side.


One aditional note on hard drives. After you've owned a hard drive for a while, the availability of large stretches of unused platter space will become scarce. The drive be cluttered with bits and pieces of data as you delete old files and add new ones.. Over time, this clutter will begin to affect performance. Your hard drive will experience fragmentation. As fragmentation grows worse, it will force the drive to spend more time repositioning the read/write heads. Eventually, performance will slow your drive's performance significantly, and can possibly cause crashes.

We recommend using a de-fragmentation software application for reorganize the files on your drive. It's automatic, easy and it can return your hard drive to maximum efficiency.

Selecting A Hard Drive.
What To Consider.
While most of our customers ask first about the capacity of the hard drive, we often take them through a quick checklist of factors to consider. The fact is, there may be differences between drives in the same "class" (i.e.: speed, interface, price).

Here is that checklist:

1. The Form Factor
Be sure to ask about the physical size of the drive. Are you utilizing a 3.5-inch bay or a
5.25-inch bay in your PC case. Currently, the best choice is a 3.5-inch drive, since
they are faster. If you have an open 5.25-inch bay and would like to install a 3.5-inch
drive, you can purchase an adapter kit. Notebook PCs use 2.5-inch drives.

2. Internal or External?
Do you have an open bay in which to install an internal drive? If not, you may consider
an external drive, which simply plugs into an adapter in the rear of your PC. External
drives are also useful when switching between PCs. NOTE: External hard drives are
normally more expensive than internal models, and offer less variety in sizes and
performance features.

3. Interface.
As mentioned earlier, information that you "save" to your hard drive travels from the PC's. main memory to the hard drive via the interface. The speed of this interface may vary
on different hard drives. Here's an explanation...

External hard drives feature two common interface types; USB (Universal Serial Bus) and IEEE 1394 (also known as FireWire or iLink). FireWire is a higher performance interface than USB, with a maximum bandwidth (the amount of data that can flow across the interface in one second) of 50MB per second. USB's maximum bandwidth is 1.5MB per second.

USB and FireWire are "plug-and-play" interfaces. This means the drives can be connected and disconnected without turning the computer off. Older PCs may not support USB or FireWire, but you can purchase an adapter card for your PC (into a PCI slot).

Internal drives are avialble in two distinct types: EIDE (Enhanced Integrated Drive Electronics) and SCSI (Small Computer Systems Interface). For performance, you'll want to go with SCSI, which is later technology and more advanced. SCSI is also more expensive than EIDE. EIDE is the most common type of interface used in personal computers today. Increasingly, many internal drives may also use the IEEE 1394 (FireWire) interface.

WHAT TO BUY: For most computer users, EIDE is the best buy. It is inexpensive and very common. If your PC activities are limited to the Internet, word processing, games, etc., EIDE is adequate. In addition, most motherboards are are equipped to handle EIDE drives. (However, many older motherboards may support only the IDE standard, which is an earlier version of EIDE).

If you require better performance, SCSI is an excellent solution. However, you may have to purchase a SCSI "Host Adapter" (sometimes called a SCSI controller card).

EIDE And SCSI Comparison

EIDE Drives				SCSI Drives
Advantages Most motherboards are set up to support EIDE drives. EIDE is easier to configure, provided you are not connecting more than 4 drives (hard drive, DVD, CD-RW, etc.). EIDE drives and other devices are much less expensive than SCSI drives. If you only have a single drive connected, EIDE is often faster than SCSI! This is due to the fact that SCSI includes a lot of additional hardware/softwqare "overhead." Disadvantages EIDE delivers slower throughput than SCSI. However newer ATA/66 and ATA/100 EIDE drives have increased performance. EIDE motherboards include 2 EIDE channels. Two drives may be connected to each channel, but only one channel can actually transfer data at a time. The second drive on the channel must wait. Although EIDE drives can be configured as part of a RAID, it is not as effective as using SCSI drives in a RAID.				Advantages Superior technology gives SCSI a faster data throughput than EIDE. This is particularly important when working with large video or audio files. More than one SCSI device can transfer data along the interface at one time, for better efficiency. SCSI has a much larger bandwidth that is fully utilized. EIDE's bandwidth is not fully utilized. SCSI devices enable you to connect up to 15 devices to a single SCSI bus. SCSI supports a wide range of peripherals, including scanners, etc. SCSI is a better choice for multitasking, configuring a RAID, extensive development work and multiple-user support. Disadvantages EIDE delivers slower throughput than SCSI. However newer ATA/66 and ATA/100 EIDE drives have increased performance. EIDE motherboards include 2 EIDE channels. Two drives may be connected to each channel, but only one channel can actually transfer data at a time. The second drive on the channel must wait. Although EIDE drives can be configured as part of a RAID, it is not as effective as using SCSI drives in a RAID.

There are two factors that dramatically affect the drive's internal data transfer rate. They
are: Areal Density and Spindle Speed. Areal Density refers to the amount of data that is
packed onto a sector. More sectors per track means that more data can be read in a
single revolution of the platter. Spindle Speed refers to the speed at which the drive spins
it platters, measured in RPM (revolutions per minute). So, the faster the platters spin,
the faster data can be read (or written). This is the basis of internal data transfer rate.

When selecting a hard drive, be sure to check the drive's "sustained transfer rate"
(STR) or "sequential transfer rate" specification. This specification tells you the amount of
data that can be read from or written to a seqential series of tracks in one second. The
specifications may also include information on "head switch time" and "cylinder switch
time." Today, high-end EIDE drives have a maximum STD of about 37MB per second.
Maximum STD will be higher than Average STD. And of course, SCSI drives will have
much higher STD rates than EIDE drives.

You may be wondering: If EIDE has a maximum STD of 37MB, what is the performance
advantage of ATA/66 or ATA/100? Most of the time, there is no speed advantage.
However, if the information you're requesting is already in the cache buffer, it can be
transfered directly at what's known as a "burst transfer rate," which can exploit the
ATA/66 or ATA/100 speed. We recommend opting for the higher ATA/66 or ATA/100
rates, since there are speed increases made when available.

Positioning Performance is the speed at which the read/write heads need to achieve
proper position over the appropriate sector for recording.

When selecting a drive, check the drive's "seek time" and "rotational latency"
specifications. Seek time is the time required to position the read/write heads over the
correct track. Rotational latency is the time it takes the drive to rotate he required sector
into position under the read/write head.

TECH NOTES: Rotational latency is determined solely by the spindle speed. The faster the platters spin, the less rotational latency. Most of today's popular drives spin at 5400 rpm or 7200 rpm. Increasingly, manufacturers are moving to 10,000 rpm, and many are available. Most 10,000 rpm models, however, are SCSI drives, and some SCSI drives spin at up to 14,000 rpm.

Obviously, the faster the platters spin, the better the performance. While 7200 rpm drives are more expensive than 5400 rpm drives, the performance is quite noticeable.

5. Capacity.
How much storage space do you need? This is simple. The bigger the drive, the better.
Just a few years ago, a 1GB drive was adequate for most users. Today. the industry
reports that 30GB is the average drive capacity. With software applications requiring an
ever-increasing amount of space to perform more complex functions---and the need for
space to download materials from the Internet, you should buy the largest hard drive
you can afford. And the larger the hard drive, it usually follows that you'll pay less per GB.

6. Manufacturer.
Spend more and get a premium brand. They offer better reliability, better warranty and
technical support.