How to Buy a Hard Drive

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Key Features

Important: Capacity

Even the relatively inexpensive PCs on our Top 10 Value Business Desktop PCs chart typically come with hard drives of at least 250GB, which is far more space than you'll need for an operating system, applications, and several years' worth of e-mail messages and typical documents. Capacity matters most to people who archive or edit digital photos, digital audio, or digital video. Video in particular can be a space hog: For example, the contents of a 1-hour MiniDV camcorder tape consume 13GB.

If you want high capacity inside your desktop, remember that you don't have to get it all in a single package: Most PCs have room for at least two internal hard drives (including your primary drive), and a typical big tower can accept even more. You'll usually save money by purchasing two 500GB drives instead of a single 1TB model at a premium. But keep an eye out for rebates and advertised specials; for example, with promotions, you may be able to find a 1TB model for the same price as two 500GB models. And of course, make sure that you have available interface ports; if not, you may have to purchase an add-in card.

External direct-attached drives come in capacities of up to 1TB for single-drive models, some manufacturers achieve the same total capacity with two 500GB drives or four 250GB drives striped together in a RAID 0 or disk-spanning configuration. Portable external drives, which use a notebook-size 2.5-inch or 1.8-inch hard disk, currently max out at 250GB. Affordable, single-drive NAS boxes range from 160GB to 1TB, while more-sophisticated multiple-drive units can be configured in various ways for capacities of up to 3TB and/or for improved speed. It's wise to go for as much capacity as you can afford--especially for a shared network drive, since multiple users are likely to fill it relatively quickly.

Somewhat Important: RAID Setup

High-end desktops and multiple-drive NAS boxes often use RAID configurations. Your motherboard or add-in drive controller must support RAID in order to use this feature.

RAID 0, the most common setup, delivers faster performance by splitting or striping data across multiple drives. Its drawback is that if one drive fails, the data on all drives is lost--so you'll need to keep your backups current.

For systems that need to minimize down time, RAID 1--in which data is written redundantly or mirrored across multiple drives--is a popular alternative. If a drive goes bad, the system can continue to run on a good one until you have the opportunity to install a new drive and rebuild the array. The drawback to this approach is that the usable capacity is only as large as the smallest drive being used--two 250GB drive paired in RAID 1 provide 250GB of storage, not 500GB, and a 250GB drive paired with a 200GB drive yields only 200GB of mirrored storage.

Typically, dual-drive RAID boxes offer the choice of RAID 0 or RAID 1. Multiple-drive direct-attached or network-attached boxes--some enclosures support up to five drive bays--generally complement those basic RAID levels with RAID 5 (parity--offering your best bet for data redundancy) or RAID 0+ 1.

You can also set up a RAID for your internal drives; however, your motherboard or add-in drive controller must support RAID.

Important: Rotational Speed

All 3.5-inch, desktop-size internal SATA hard drives--as well as most current PATA drives--spin their disks at 7200 rpm. A handful of drives spin at 10,000 rpm; they are aimed at enthusiasts and enterprise users. Typically, the faster the disks spin, the faster the data is read and written--but the average buyer won't want to pay a price premium for a 10,000-rpm model.

Portable external drives have the biggest range in rotational speeds. Models are currently available in 4200-rpm, 5400-rpm, and 7200-rpm flavors. The most common of these is 5400 rpm. You'll see a difference in transfer speeds if you copy a lot of data--say, photos from a full 2GB memory card--to your hard drive, so keep a close eye on these specs, and beware of vendors that don't identify the drive's rotational speed.

Somewhat Important: Seek Speed

Average seek speed, measured in milliseconds, refers to how fast, on average, drives can find a particular piece of data. This is a minor consideration: For most people, the effect of differences on this measure in everyday use is negligible. The exception is when a drive is called upon to assemble many small pieces of data scattered in different areas of the hard drive, such as when copying large folders full of many small files. Jumbo drives tend to have somewhat longer seek times.

Important: Interface

Nearly all internal drives in new PCs use the SATA interface, which supports maximum transfer rates of either 150MB or 300MB per second. The drives with a 300MB-per-second maximum transfer rate cannot take advantage of their wider bandwidth in typical desktop use, though they shine in RAID combinations.

PATA drives, which support maximum transfer rates of either 100MB per second or 133MB per second, are still widely available. There's little advantage to one or the other; hard drives never sustain data-transfer rates approaching either maximum, though drives can sometimes push out of data at rates approaching the high-end speeds for brief bursts.

Both PATA and SATA interfaces are backward-compatible: For example, you can run an older ATA-33 drive on an ATA-133 bus or a 150MB-per-second SATA drive on a 300MB-per-second bus. But although PATA-to-SATA adapters are available, you should match a PATA drive to a PATA interface whenever possible, to get the best performance from it. SATA drives work with the SATA interface only. Inexpensive PCI Express and PCI add-in cards are available that let you add a SATA interface to a computer that lacks it; PATA and PATA/SATA models are available only for PCI.

Most external drives have a USB 2.0 interface or a dual USB/FireWire interface. Other interface configurations are dual USB2.0/FireWire 400; FireWire 800; and eSATA. USB 2.0 and FireWire 400 perform slightly slower than a comparable internal drive, but either is more than acceptable for auxiliary storage or backup. (A USB 2.0 drive will work with a USB 1.1 port, but its performance slows to an unacceptable level.)

FireWire 800 is quite fast, but this interface is relatively rare on desktop PCs. For high-performance external storage, go with an eSATA direct-attached drive. These drives are becoming increasingly popular; and while they don't offer the universal connectivity of a USB 2.0-enabled drive, they're as fast as an internal drive--and sometimes they include a USB connection, for good measure.

To install an eSATA drive, you'll need an open external port: Though eSATA drives come with a pass-through connector that provides an external port, you'll need an open internal SATA port to attach the connector to. If you don't have an open internal port but do have an available PCI slot, an inexpensive PCI add-in card can provide external SATA, USB 2.0, or FireWire ports for systems that lack them. Likewise, you can find PC Card adapters that add USB 2.0 and FireWire ports to a notebook, if your system is so old that it lacks these interfaces. However, FireWire and FireWire 800 use different connectors, so they are not cross-compatible.

Consumer-level NAS devices generally employ the TCP/IP protocol and a 10/100Base-T or gigabit ethernet connection to hook up to your network. As such, NAS devices are generally pokier than direct-attached external models. Look for NAS devices that provide USB 2.0 ports for accommodating additional hard drives so you can expand capacity or share attached printers across the network.

Somewhat Important: Buffer

When a system requests data, a hard drive will fetch what is requested and load its buffer memory with extra information that the processor is likely to ask for next. Theoretically at least, a larger buffer size should help keep the data flowing better, especially in disk-intensive tasks such as file searching. Most desktop drives--and all of the ones on our Top 5 charts--have buffers of either 8MB or 16MB. Value-priced PATA drives may have 2MB buffers.

Somewhat Important: Noise

If you are building your own PC to use in your living room as a media center hub, noise may be a significant issue. Many hard-drive makers offer versions of their drives designed for use in personal video recorder or media-streaming environments. Look for these specialty drives if you're looking to reduce the noise output by your system.

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