Hard-Disk Buyers' Guide (JC)

Let's face it—your hard disk is full. How do we know? Well, if you're like us, you've probably built up a massive collection of MP3s and digitally edited a cinematic masterpiece of your vacation in Hawaii, and now you don't have enough space to install the latest version of Quicken. Even if you don't fall into that category, in general you need more disk space to do more things. But should you buy an internal hard disk to replace the shrinking one you currently own, or simply add another hard disk and use them both? Perhaps you want to connect your new drive externally to one of your Mac's peripheral ports. Buying a new hard disk is a hard choice, but sit tight as we help you make an informed decision.

What's Inside?

If you don't already know what kind of hard drive you have installed inside your Mac, your first mission is to find out. Knowing this will aid in choosing the proper interface and help you decide whether you need an internal or external drive.

The manual that shipped with your Mac is a good place to start, as Apple frequently provides details on storage-expansion capabilities. If your manual is missing in action, you can get a copy from Apple Support at www.info.apple.com/manuals/manuals.taf. (You'll need Adobe Acrobat Reader to open the file—download the software free from www.adobe.com/products/acrobat/readermain.html.) Find more details at Apple's Tech Info Library (http://til.info.apple.com).

Another useful tool to assist in your quest is the Apple System Profiler, installed as part of your system software. It provides detailed information about your Mac, its components, and your installed software. Find it in the Apple menu in Mac OS 9 and earlier and in the Utilities folder in Mac OS X.

To get technical information about your hard disk, launch the Apple System Profiler and select the Devices And Volumes tab. Click the triangle next the hard drive to reveal details like capacity and interface. Note that your Mac's internal hard drive is either an ATA or a SCSI device.

Many Macs have a bar-code label affixed on the back that details what's installed inside, such as memory configuration, processor speed, and cache size, hard-drive capacity.

Besides your internal hard disk, your Mac has other ways of addressing storage devices. These technologies may include SCSI, USB, or FireWire. Again, the Apple System Profiler is likely the best way to find out what kind of connections your Mac supports. Beyond that, you can also inspect your Mac visually and check out its expansion ports.

The Eternal Question: Internal vs External

One burning question that frequently crosses the minds of storage-seeking Mac users is what kind of hard drive to buy, internal or external.

Internal drives are installed inside your Mac. Sometimes known as hard-disk mechanisms, they are self-contained units—that is to say, they come equipped with everything they need to function. As you've probably discovered, your internal hard disk uses only one of two types of interface for communication—ATA or SCSI.

It may surprise you to know that Apple doesn't actually manufacture your hard disk. As is the case with many other components, Apple buys drives from all the major vendors—Western Digital, Seagate, Quantum, IBM, and others—and brands them with an Apple label before installing them inside your Mac. So if you decide to replace your internal hard drive tomorrow, rest assured that whatever brand of drive mechanism you choose, it will likely be fully Mac compatible.

Sometimes choosing an internal drive means you must simultaneously replace your current hard disk and move your data to a new drive (for more on this subject, see “Backup Devices and Removable Storage,” later in this chapter). This is true if you own an iMac, an iBook, or a PowerBook because these models don't offer any internal space for an additional hard drive.

No matter which Mac you own, you have options for connecting external drives. An external drive houses the hard-disk mechanism in a box known as an enclosure. A drive with this extra feature typically costs $70 to $100 more than an internal, uncased hard-disk mechanism. The enclosure has a fan, a power supply, and sometimes additional electronic circuitry to run the drive. Because you can attach external drives to your Mac via the USB, SCSI, or FireWire port, you have your pick of a wide variety of devices.

Although they cost slightly more, external drives offer some real advantages over internal models. Specifically, you can transport the drive easily if you need to move large amounts of data between Macs. Adding an external drive is also easier than installing an internal one, and when you graduate to a new Mac, you won't have to remove the drive—just unplug it and go.

What's an Interface?

The interface refers to the method by which peripherals connect to your Macintosh. In this case we're talking exclusively about storage devices. USB, SCSI, ATA, and FireWire devices use different kinds of interfaces to communicate with your Mac.

Each of these technologies is unique and has its own set of benefits and limitations. The following section offers an overview of the various storage interfaces. The sidebars expand on useful technical tidbits.

ATA and IDE.

If you've bought a Macintosh in the last eight years, it probably has a built-in IDE hard disk connected to the ATA bus. Sometimes known as ATA or EIDE (Enhanced Integrated Drive Electronics, the second generation of IDE) drives, these devices are the least expensive type (current prices hover around $200 for 20 GB and up), offering high capacity at a low cost. An excellent value, they provide moderate to very good performance.

SCSI.

Die-hard Mac fanatics are already familiar with the many faces of SCSI (pronounced scuzzy, even though it isn't). The most significant advantage SCSI drives have over ATA drives is performance, but you may not notice if you use your Mac for commonplace tasks like Web browsing or word processing. The key to SCSI's performance is throughput (something we cover in more depth below).

Realistically, you should invest in a SCSI drive if you crave maximum perfor-mance. These drives are almost a necessity for digital-audio and video editing, 3D rendering, and other disk-intensive applications. Performance comes at a price, as always, so expect these drives to cost roughly $200 more than more-economical IDE drives with identical capacities. You might also have to add a PCI SCSI card, which ups the price a bit more.

ATA and IDE: Simple but Limited (KD) Apple introduced its first ATA drive on a Mac in 1994. ATA (AT Attachment; the “AT” is a vestige from the early PC days) and IDE (Integrated Drive Electronics) are interchangeable terms. The first ATA drives, though plentiful and inexpensive, were slower than the SCSI drives Apple had been using. However, newer generations of ATA are substantially faster. ATA is cheaper because it integrates the controller onto the disk drive itself. PC (meaning non-Mac) manufacturers adopted this cost-efficient technology early on in the development of the personal computer. Since parts always cost less when a vendor can make many simultaneously, ATA drive prices kept falling as the technology became more popular. You can now buy an ATA drive for $100 less than a SCSI drive with the same rotation speed and capacity. ATA comes in different types. The first version of ATA supported one or two hard drives on a 16-bit interface. ATA-2, also known as Fast ATA or Enhanced IDE (EIDE), is faster and supports ATAPI, a protocol for attaching CD-ROM, Zip, tape, and other non-hard drives. Ultra-ATA, also called Ultra-DMA, ATA/33, or DMA-33, supports multiword DMA and can transfer data at as fast as 33 MBps. (A “word” is 2 bytes, so a single-word DMA moves data a word at a time. Multiword DMA moves data in bursts.) ATA/66 doubles ATA's throughput to 66 MBps. Apple currently includes ATA/66 in its latest systems. Although the specifications for a 100 MBps version of ATA are not final, ATA/100 drives and chips are on the market, and it is only a matter of time before Apple incorporates them into new Macs. Although originally designed as a simple way to install a single hard drive in a computer, ATA currently supports as many as four devices—a master and a slave on each of two ATA channels. The master drive doesn't actually dominate the slave drive; these are simply distinguishing names. The first Mac to allow slave drives was the beige Power Macintosh G3 with the second motherboard revision. The simplest way to find out if you can add a slave drive to your beige G3 is to run the Apple System Profiler. If the ATI graphics chip on your motherboard is an ATI Rage Pro chip, not a plain ATI Rage, you can add a slave drive. Adding a second internal ATA drive is a fabulous way to increase your storage for a reasonable price. A Power Macintosh typically comes with the hard drive on the first channel and the CD-ROM drive on the second. You can use the Apple System Profiler to check how many ATA or ATAPI devices you already have. You should add the second drive to the same channel as the first drive. Set your startup drive as the master and the second drive as the slave by changing their jumper connections. Often the drive has a small diagram showing you the proper jumper settings. If not, consult the drive manufacturer's Web site. Once you've set the jumpers properly, you can connect them in any order. When it comes to ATA drives, Mac users needn't feel PC envy—practically every current ATA hard drive is Macintosh compatible. You can purchase a drive at outlets ranging from Costco to an online retailer such as Outpost.com (www.outpost.com). Like SCSI, ATA is backward and forward compatible, meaning you can put an ATA/33 or ATA/100 drive on your ATA/66 bus. Once you've added a new drive, use Apple's Drive Setup in the Utilities folder to format it. For more tips on installing an ATA drive, check the Macworld Web site (www.macworld.com) or Accelerate Your Mac (www.xlr8yourmac.com). Unless you decide to add an internal hard drive or replace your CD-ROM drive, you may never have to worry about your ATA bus at all. All of the drive utilities (with the exception of RAID software) work the same way with ATA and SCSI drives. ATA is a convenient, straightforward technology for use inside your computer, but for external connectivity, FireWire, USB, or even SCSI is a better choice.

SCSI: Gone but Not Forgotten (KD) In 1986, when Apple built SCSI into the Mac Plus, it was a revelation in connectivity. SCSI was the first easy way to connect multiple devices such as hard drives, scanners, or printers to a computer. However, as peripherals became faster and more plentiful, SCSI aged less than gracefully. Since 1999 Apple has been abandoning the familiar SCSI DB-25 connector. In its place are USB and FireWire connectors for external devices and ATA for internal drives. Although Apple had good reasons to forgo SCSI, reasons remain for considering it. Anyone with an older computer can continue to use this handy connection option. Those who have recently purchased a newer system may want to preserve their investment in SCSI devices. Last, the latest versions of SCSI, though expensive, are blindingly fast. People often refer to configuring SCSI as black art or voodoo. Don't let them scare you; the basic rules are simple. However, the more devices you add to your SCSI chain, the more likely you are to encounter troubles with termination and cable length. Each SCSI device must have a unique SCSI ID between 0 and 6. Most external devices provide a simple dial or wheel to set the ID. On an internal drive, you use jumpers the size of a grain of rice. On older systems—made before Apple switched to ATA for internal devices—both internal and external SCSI devices use the same SCSI bus, with the internal hard disk set to ID 0 and the internal CD-ROM to ID 3. Rules of SCSI Termination You must terminate the first and last devices on a SCSI bus. Termination stops the electrical data signal when it gets to the end of the SCSI chain, thus preventing it from reflecting back across the bus and causing data errors. If the first device on the Macintosh is an internal hard disk, you must terminate that device. Apple installs internal drives with termination. SCSI also has restrictive cable rules. The faster the type of SCSI, the shorter the allowed cable lengths. SCSI I, the type of SCSI on the back of the Macintosh, transfers data at a maximum 5 MBps and allows as much as 18 feet of cable. However, the more modern Ultra SCSI—which supports 20 MBps—allows a total cable length of just 3 feet. SCSI comes in two major types, Narrow and Wide, which describe both the bus and the type of device. Wide is double the speed of standard SCSI and uses denser cables and connectors. Wide also allows as many as 15 devices. The fastest flavor of SCSI is Wide Low Voltage Differential Ultra 3, which can move data at a blazing 160 MBps. That translates into 1,280 Mbps, making FireWire's 400 Mbps look pokey. Before you get dizzy at the thought of all that speed, remember that you can only use it if you have peripherals that also go 160 MBps. As SCSI has gone through many generations, it has managed to remain backward and forward compatible. You can put an old, slow device on the newest SCSI card. Likewise, you can connect a new device to your old Mac. Although you won't get optimum speed if you mix generations, this compatibility does preserve your investment in peripherals. One exception—don't hook up a Wide device to a Narrow card. If you have an older computer with built-in SCSI, you may not want to invest in new SCSI devices. The SCSI on the back of your Mac transfers data at 5 MBps, much slower than FireWire or current SCSI. Also, when you do buy a newer system, you will have difficulty moving over your SCSI devices. A better idea is to buy a PCI FireWire card for less than $100 and then get the latest FireWire devices. SCSI Cards If you own a desktop Mac such as a Power Mac G3 or G4, you've got lots of room for PCI-card expansion, including a high-speed SCSI card (sometimes known as a SCSI adapter). SCSI cards fill the void Apple left when it abandoned SCSI as its standard drive interface in favor of low-cost IDE drives. In the last few years, Apple has made SCSI cards an option on many of its G3 and G4 models. But if you weren't lucky enough to get one when you bought your Mac, you can easily add it later. Adaptec (www.adaptec.com), ATTO Technology (www.attotech.com), and other third-party manufacturers offer SCSI cards with transfer rates as fast as 160 MBps.

FireWire.

Also known as IEEE 1394, FireWire is capable of moving data at 400 Mbps, but realistically most of today's drives can't deliver this kind of performance. FireWire drives plug into the external FireWire port (although some Power Mac G4 models offer an internal port as well). High-capacity drives start around 20 GB and increase from there.

You can hot-swap FireWire drives—that is, unplug or plug them in while the Mac is running—and they don't involve the hassles of ID, termination, and limited cable lengths. FireWire drives offer decent performance, are supereasy to hook up and use, and are available at modest prices.

USB.

This is currently the slowest method of moving your data, but it may be your only option if you own an early iBook or iMac with a USB port. Most USB hard drives can move data at a top speed of just 1.5 MBps, which is very slow when you compare it with any of the other technologies we've described. But USB drives offer some real benefits. For one thing, they tend to cost less than any other type of external drive, and like FireWire they are extremely easy to hook up and use. A new USB specification (USB 2.0 or Hi-Speed USB) promises to push performance up to 480 Mbps (60 MBps).

Capacity.

After figuring out how your new hard disk will connect to your Mac, you should next think about capacity—the amount of storage space you need for current data and free space you require for future expansion. First and foremost, purchase the largest-capacity drive you can afford, especially if you work with graphics, databases, and video or sound files. Buying a hard disk with more space than you currently need is a good idea, since your requirements will keep expanding.

When looking at the capacity of a new hard disk, keep in mind that some areas of the disk contain directories and other data, so you never get to use the drive's entire capacity. It's not uncommon to lose about 5 percent of the total capacity on an initialized (formatted) drive.

FireWire: Setting the Macintosh Ablaze (KD) Apple has pushed SCSI out of the nest in favor of FireWire. This standard has a lot going for it, including speed and ease of use. Many computer companies agree with Apple—it has become very common on the PC side as well. Although this Apple-developed technology was adopted as a standard in 1995, Apple didn't include FireWire on a Macintosh until January 1999. The first Macintosh with FireWire was the Blue-and-White Power Macintosh G3. Apple has included FireWire on subsequent Power Macintoshes, as well as the iMac DV, iBook (FireWire), and the second-generation PowerBook G3. You can add FireWire to older Macs by installing a PCI card or PC Card. FireWire cabling is simple and hot swappable. The cables are thin and come in more-generous lengths than SCSI ones. FireWire also frees you from termination and setting IDs. FireWire is much faster than USB, which operates at only 12 Mbps—FireWire operates at 400 Mbps. If that isn't fast enough for you, 800 and 1,600 Mbps versions of FireWire are on the drawing board. The maximum cable length between devices is 4.5 meters; from the computer to the last device the limit is a whopping 72 meters. Although FireWire supports 63 devices, it will only connect 16 devices or hubs in a row. You can reach 63 devices by adding hubs. For example, after connecting 14 devices in a row, you could add a 5-port hub, putting all devices connected to that hub just 16 hops from the computer. FireWire also provides limited power—as much as 60 watts—over the cable. Low-power devices, such as small hard drives, don't need an external power source. FireWire particularly suits consumer-oriented digital products, including digital camcorders, because it provides both high-bandwidth and isochronous transfers. When you copy a file to a hard drive, you probably won't notice if the transfer pauses for half a second. However, if your favorite song stops for this long, it's infuriating. Isochronous transfers guarantee that a stream of data will get a certain amount of bandwidth, so that the stream won't get interrupted. Today you can buy FireWire hard drives, scanners, printers, camcorders, and CD-R drives. However, many of these devices contain a bridge chip that translates from the device's native interface—for instance, IDE—to the FireWire interface. This extra bit of electronics means that you pay a modest premium for FireWire devices and that they may not deliver their maximum performance. The FireWire specifications include peer-to-peer connections, which offer the potential for a slew of convenient and powerful features. Someday soon, you may be able to connect a FireWire camcorder to a FireWire hard drive and start a download—without a CPU. You can use FireWire in place of Ethernet to connect computers to each other or to a shared peripheral. Indeed, FireWire may be the home-electronics connection of the future, connecting your stereo, TV, DVD player, and game console.

So What's ATAPI? Earlier we mentioned the Apple System Profiler as an important tool, useful for identifying the type of hard drive you have installed. If you had an opportunity to look at the information provided, you may have noticed that it lists your CD-ROM, DVD-RAM, and even DVD-ROM drives as ATAPI (AT Attachment Packet Interface) devices. ATAPI is a low-cost interface that relies on an ATA connection and almost exclusively serves removable-media drives. The basic facts are as follows: You can have just one ATAPI device in your Mac, and in most cases it is a CD-ROM, DVD-RAM, DVD-ROM, or Zip drive. Drives that use ATAPI are typically inexpensive and require internal installation.

Sizes and shapes (HN, JC).

Two physical dimensions commonly categorize drives: the diameter of the platters inside and the height of the whole sealed mechanism. Known as the form factor, these dimensions constitute the standard sizes that make units from different manufacturers interchangeable.

There are five form factors: full height, 5.25-inch diameter; half height, 5.25-inch diameter; half height, 3.5-inch diameter; low profile, 3.5-inch diameter; and low profile, 2.5-inch diameter.

Most modern hard disks are 3.5-inch low-profile models only 1 inch high; you'll find these inside almost every desktop Mac from the SE/30 to the Cube and beyond. The 2.5-inch drives are installed inside PowerBooks and iBooks. Removable drives such as CD-ROM and DVD-ROM are half-height 5.25-inch devices.

Drive performance (HN).

There's no single index for measuring hard-disk performance. If you care about maximum speed, pay attention to several variables and weigh them differently depending on your Mac and what you plan to do with it.

The simplest variables are the average seek time and the average access time, both measured in milliseconds (ms). The average seek time is how long it takes the heads to move to the desired track; nowadays, it can be anywhere between 3 and 12 ms, depending on the type of drive interface (SCSI or ATA). The average access time is the sum of that figure plus an additional, smaller amount (normally about 2 to 3 ms) for latency, the average wait for the desired sector to come around under the heads once they get to the right track. Unfortunately, many vendors use these terms inconsistently; some will even tell you they mean the same thing. If milliseconds matter to you, make sure you're using the same standard when comparing products. A drive with an average access time of 15 ms is actually faster than one with an average seek time of 12 ms.

Throughput or transfer rate.

Data transfer rate is a measure of how fast a drive can deliver data to the Mac once it gets to the sectors it's looking for. The transfer rate is counted in megabytes per second (or sometimes, just to confuse things, megabits per second). Today's drives have transfer rates from 5 all the way up to 320 MBps. This figure depends on the interface—ATA or SCSI, for example.

If you deal mostly with small files like word-processing documents, transfer rate is less important than seek or access time, because your drive will spend more time getting to the data you need than transferring it to the Mac. When you open a letter created in Word, your Mac doesn't have to read large amounts of data, so even large differences in the transfer rate have negligible consequences. But if you work with large scanned images in Adobe Photoshop or with big QuarkXPress layouts or giant QuickTime files, transfers actually take whole seconds, so differences in the transfer rate matter—in terms of seek or access time, you won't encounter differences of more than a few thousandths of a second.

There's also a difference between burst transfer rates and sustained transfer rates. The former measures how fast a drive can pump out a small amount of data loaded into memory buffers on the drive controller; the latter is how fast it can deliver larger amounts even after the buffers are empty. Burst rates are much higher, so some vendors focus on those, but for most purposes the sustained rate is more important because it is a better indicator of real-world performance.

Spindle speed.

The standard spindle speed—the rate at which a hard disk's platters rotate—used to be 5,400 rpm. In the last few years drive manufacturers have been delivering drives that spin at 7,200, 10,000, even 15,000 rpm. The extra speed reduces latency, but its main benefit is to boost sustained transfer rates: The faster the disks are spinning, the faster the drive should read in all the data it's after. You'll notice the difference mainly with big files.

Reliability.

Drive manufacturers measure the durability of their drives in terms of mean time between failures (MTBF)—the number of average power-on hours a drive will last before some component gives out. For most new drives the figure runs from about 500,000 hours to 1.2 million hours.

However, 500,000 hours works out to 57 years and 1.2 million hours adds up to 137 years, so these claims are not based on actual field experience— lab testers derive them by running a bunch of drives simultaneously and extrapolating from the rate of breakdown during the test period.

Still, MTBF probably means something, at least as an indicator of relative reliability, so it's worth considering when you are choosing a product. But try to supplement this rating with reviews in Mac publications and first-hand reports from users.

Warranty.

The length of time a drive remains under warranty is an extremely important consideration. Expect a warranty period of at least one year for most drives and as long as five years for some.

Should the drive mechanism or any components inside an external case fail (the power supply, fan, and so forth), the vendor will typically replace the drive at no charge. It will not, however, cover the cost to recover or re-create any data lost as a result of a drive failure, so back up your hard drive religiously.

Disk Images: So Real, You Just Click (SA) Disk images often serve as the medium of transfer for software downloads from Web sites: You obtain the disk image, put it on a floppy or mount it as a virtual floppy, and access the information. The Disk Copy utility that comes with your system software creates and later interprets all disk images. The file Disk Copy makes and interprets is called a disk image file. Its icon looks like a document (it has a turned-down corner) with an image of a floppy icon on it. Disk Copy can also make disk images of floppy disks and CD-ROMs.