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There are two main interfaces used today: Enhanced Integrated Drive Electronics (EIDE), and Small Computer System Interface (SCSI, pronounced "scuzzy"). SCSI drives perform better and have features that provide for higher reliability than EIDE drives. Not surprisingly, they are much more expensive than EIDE drives, and thus are used mostly in mission-critical business applications, and rarely in standard PCs. Because of this, SCSI devices are generally beyond the scope of this book, although some of the information in this chapter applies to SCSI also. There is a new interface, just becoming available as of this writing: Serial ATA (SATA). SATA drives are set to replace EIDE drives, and many new motherboards have connectors for both types.
We divide the factors to consider when selecting a hard drive into two categories: compatibility and quality.
The following factors must be considered to make sure a hard drive will work in a given system:
Form factor: Hard drive form factors aren't the same as other form factors. They have to do only with fitting the drive in the case, and thus are applicable only with internal hard drives. Desktop and tower computers are standardized for the 3.5-inch form factor, although it is possible to use smaller drives in one of these computers. (We discuss installing a small hard drive in a full-sized system later in this chapter). Laptops take 2.5-inch drives or smaller; check with the laptop documentation or Web site, or remove the drive and look at the label.
Ultra Direct Memory Access (UDMA) speed rating: This refers to the speed of data transfer between system memory and the hard drive buffer measured in megabytes per second and, at the time of this writing, has possible values of 33, 66, 100, and 133. Check the motherboard's maximum transfer speed and select the fastest hard drive the user can afford. Motherboards can accept any drives rated at their maximum speed or slower.
EIDE or SATA: As of this writing, some new motherboards have connectors for both, but older boards accept EIDE only. SATA expansion cards for PCI slots are available.
Any time you are purchasing a hard drive that is to be the main or only hard drive in a computer, you should take the following quality indicators into account. A cheap hard drive will provide poor performance in most cases, but might be well suited for file archiving when the files aren't accessed often.
Here are factors to consider when attempting to purchase the highest quality hard drive for the money:
Warranty: Previously, many hard drives came with a three-year manufacturer's warranty. More recently, one-year warranties have become most common. Try to get three years if possible.
Buffer (cache memory): This is high-speed memory that is used to store a small amount of data while it is waiting to be read from or written to the drive. As this significantly improves performance of the computer, the bigger the buffer, the better. 2MB is good; 8MB is much better, especially when the user works with graphics-intensive programs such as video editing or games, or other high-stress programs. Drives with less than 2MB of cache will likely provide poor performance.
Platter speed: The most common speeds are 5400 and 7200 revolutions per minute (RPM). The faster the platter spins, the faster data can be accessed and transferred.
EIDE or SATA: EIDE drives are the ones that PCs have been using for many years now. SATAs are just being introduced as this is written. SATA drives perform faster and more accurately than EIDE. An added advantage is that SATA cables are small, making for easier installation and better airflow than the standard ribbon cables used on EIDE devices. The smaller cables also allow for smaller computers.
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