Learn about Hard Drives

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What Size Should I Buy?
The Bigger the Better—Usually

How Do I Choose Between IDE, SATA and SCSI?
When to Choose IDE
The basics of SATA
Storage Interface Evolution
Why SATA
When to Choose SATA
Glossary
When to Choose SCSI

What Specs Should I Look For?
Take Specs With a Grain of Salt
Transfer Rate
Average Access vs. Average Seek (and Latency)
Rotational Speed
Density
Interface
Capacity
Form Factor

How Much Should I Spend?
Replacement or Additional Drive: $200 to $300
Extending the Life of an Old PC: $100 to $200
Shipping: $10 to $15

What Do I Need to Install a New Drive?
Available Drive Bay
SCSI Card for SCSI Drives
Consider File-System Limitations

What Storage Alternatives Do I Have?
Removable Drives

Can I Upgrade the Drive in My Notebook?
Probably, But Check With the Manufacturer

How Should I Pay?
Always Use a Credit Card
Avoid Restocking Fees

How Do I Choose a Reliable Brand?
Know Thy Warranty
Ask Other Buyers

What Size Should I Buy?

The Bigger the Better—Usually

The rule of thumb for hard drives has always been that you can never have too much storage, so you should buy as much as you can afford. In general, that's still true, even though you can now buy 100GB or more of storage for well under $200.

Buying lots of capacity is smart because data files tend to grow to fill the available space. Careful users try not to clutter up their disks with unnecessary files, but more and more software fills up the space for you, on the grounds that with today's hard drives you can lose 1GB or so without noticing it. As the trend continues, however, it's likely that a drive that seems overly generous today will run out of room at some point in its lifetime. The bigger the drive, the less likely that will happen—or, at least, the longer it will take.

There are some limitations on capacity. The obvious one is that higher-capacity drives cost more than low capacity drives, even though the price per gigaabyte goes down. Another issue is that for any given budget, you may decide to go with a slightly lower capacity for the sake of better performance. Note too that if you have an older computer, you may run up against BIOS limitations for how large a capacity the computer can handle.

How Do I Choose Between IDE, SATA, and SCSI?

When to Choose IDE

If you need a drive for a workstation or stand-alone system, you'll generally want an IDE drive for a simple reason: Given Identical drives, IDE will offer the same performance for a lot less money.

An IDE drive can actually save money in two ways. First, the drive itself will be less expensive because other interfaces costs more than an IDE interface—often as much as $200 more for an otherwise identical drive. Second, if you don' t already have a SATA or SCSI controller in your system, you'll have to buy one at prices ranging from under $100 to several hundred dollars, depending on the type of connection you need. Unless you have a truly ancient system, your computer can almost certainly support up to four IDE drives with no additional hardware.

The basics of SATA

Serial ATA (SATA) is the next-generation interface standard for low-cost direct-attached storage in desktop PC, workstation, and entry-level server environments. As a serial technology (bits transmitted in a single stream, rather than along parallel paths) SATA eliminates the restrictions on performance, reliability, and scalability that are inherent in today?s parallel ATA (IDE) standard. Because SATA cost-effectively enables RAID protection, is easily scalable, and has a high performance roadmap, it will become the dominant direct-attach storage interface for budget-conscious users.

Storage Interface Evolution

When it was introduced nearly twenty years ago, parallel ATA, also known as IDE, provided a simple low-cost storage interface standard that met the performance and flexibility needs of desktop PCs. Concurrently, the more robust and costly SCSI interface evolved to fulfill the higher performance, reliability, and scalability requirements of enterprise-class applications. However, as CPU capabilities and the complexity of applications and data types accelerate, technology restrictions limit the future applicability of parallel interfaces. To better meet future processing needs, both ATA and SCSI are moving to more flexible and capable serial technology. Over time, SATA for the low-end and Serial-Attached SCSI (SAS) for the high-end will become the industry standard storage interfaces.

Parallel vs. Serial Interfaces

Interface Technology Transfer Rate Cabling Connectivity Connectivity

Current Planned

ATA/IDE - Parallel - 133 MB/s - At max today - Wide ribbon
- 40-pin
- 18-inch length - 2 drives per channel
- Master/slave relationship
- Shared bandwidth among drives

SATA - Serial - 150 MB/s - 600 MB/s - Thin, round ribbon
- 4-pin
- 1-meter length - Single drive per channel
- Point-to-point connection
- Full bandwidth per drive

SCSI - Parallel - 320 MB/s - None planned - Wide, round ribbon
- 68-pin
- 12.5 meter (LVD) length - Up to 15 devices per channel

SAS - Serial - 300 MB/s - 1200 MB/s - Thin, round ribbon
- 6-meter length - 128 devices
- Expanders allow up to 16,000 devices

Why SATA?

SATA has been developed as a backward compatible, evolutionary replacement for ATA. Employing a serial technology version of the ATA design, SATA offers compelling technology, performance, and usability benefits for data-intensive applications in direct-attached storage environments. Within the next three years SATA will replace ATA/IDE as the low-cost interface-of-choice.

Serial ATA

Features Benefits

- High performance roadmap
(1.5 to 6.0 gigabits/sec) - Scalable performance growth

- Lowest-cost per megabyte - Wide market appeal

- Command optimization - Makes SATA RAID more practical

- Point-to-point connections - Greater data reliability

- Full backward compatibility - Easier, faster, cheaper migration

- Single thin 1-meter cable - Greater flexibility; space savings

- Backplane connection Hot-plug/hot-swap flexibility - Hot-plug/hot-swap flexibility

When to Choose SATA

The low-cost/high-benefit nature of SATA makes it an ideal fit for budget-conscious desktop, high-end workstation, and entry-level server users whose application needs require high performance without either the additional robustness, or the external connectivity features of SCSI technologies.

Interface	Cost	Optimal Data Type	Storage Environment	Application Environments
ATA/IDE	- Low	- Reference data: low frequency access, sequential data; e.g., file sharing, email, web, backup, archive	- Internal DAS	- Desktop PCs
SATA				- Desktop PCs, workstations, entry-level servers
SCSI	- Moderate	- High-frequency transactional & random access data; e.g., database, online purchases, OLTP, CRM	- Internal DAS & External NAS/SAN	- Mission critical enterprise servers, networked storage
SAS				- Mission critical enterprise servers, large-scale networked storage

Glossary

ATA "Advanced Technology Attachment," a storage interface designed over 15 years ago and now the de facto I/O standard for desktop PCs. Though adequate for low data-demand applications, the combination of increased CPU capabilities, greater application through-put demands, and faster, more capable hard drives, severely limits the future usefulness of this interface.

Command Optimization Commands to a device are queued for immediate execution, without having to wait for responses, increasing performance and making RAID more practical.

CRM "Customer Resource Management" software.

IDE "Integrated Device Electronics," the current low-cost storage interface standard for desktop and portable PCs, synonymous with ATA.

NAS "Network Attached Storage," a storage design that connects a server to externally enclosed hard drives via a local area network.

OLTP "Online Transaction Processing" database.

Parallel Technology A design that allows a device (hard drive) to receive multiple bits of information at the same time. Parallel interfaces use short, wide cables carrying multiple signals, and pose inherent design limitations on data transfer speed and multiple device connections.

Point-to-Point Direct connection between the backplane and the storage device, allowing for the high-performance, full utilization of bandwidth.

SAN "Storage Area Network," a storage design that connects all the storage devices on a network with all the servers on a network for enhanced reliability and performance.

SAS "Serial Attached SCSI," the serial imple-mentation of the SCSI standard, providing greater flexibility, performance, reliability, and connectivity.

SATA "Serial ATA" is an evolutionary replacement for the Parallel ATA physical storage interface.

SCSI "Small Computer System Interface," the predominant storage I/O technology for high-reliability, high-performance server applications.

Serial Technology A design that allows data to be sent one bit at a time. Serial interfaces use thin cables, and are capable of faster speeds, greater reliability, and more flexibility in attaching multiple drives.

When to Choose SCSI

SCSI is the obvious choice for a good choice for power users and server builders. A key advantage for networks is that the SCSI interface is designed to handle simultaneous data requests—from multiple users, for example. It calculates the most efficient way to processes the requests, then processes them with the minimum necessary head movement and drive rotation. SCSI also allows more drives than IDE's maximum of four. Most SCSI cards let you add up to fifteen SCSI devices per channel.

Of course, better performance costs more, so for any given capacity, you may have to pay several hundred dollars more for a faster SCSI drive over and above the $150 to $200 premium you'll pay for SCSI compared to an IDE drive of identical capacity. Note too that if you get a SCSI drive, you'll also have to get a SCSI adapter if you don't already have one. The adapter can cost anywhere from $90 to several hundred dollars, depending on the highest SCSI version it supports.

What Specs Should I Look For?

Take Specs With a Grain of Salt

When you look at drive specifications, keep in mind that there are only two easy cases for predicting performance based on specifications. If one drive outdoes another on every single performance specification, it's a safe bet that it will offer better performance. Similarly, if two drives match in all but one specification, the one that does better in that one specification will be the better performer. Beyond that, judging performance by specifications is almost impossible, because the performance depends on several factors and the balance between them. Still, there are some basic indicators that can help you make rough comparisons.

The two specifications you should care most about are two that you'll rarely see advertised: average sustained transfer rate and average access time. All the performance specifications you see most often—burst transfer rate, internal transfer rate, rotation speed, average seek time, latency, and density of data on the disk—matter only because they affect these two key specifications.

Transfer Rate

There are several kinds of transfer rate, and they are not interchangeable, so be careful when comparing drives.

Internal transfer rate measures the speed that data can move between the drive head and the drive platter. This is usually the limiting factor in transferring data to and from the drive.
Burst transfer rate is the maximum speed of the interface. This is always faster than the internal transfer rate. The only time a drive will transfer data at the burst rate is when moving data to and from the memory buffer in the drive
Sustained transfer rate measures the speed that data can move between the drive and the computer for sustained periods of time.

The transfer rate you'll see most often is the burst transfer rate, because it's the most impressive number of the three. But the number that matters most is the sustained transfer rate, which essentially tells you how quickly large amounts of data can move to and from the drive. Most of the time, the drive will have to read from or write to the disk platter itself, which means the sustained transfer rate depends primarily on how quickly the drive can move data between the drive head and the disk. The sustained transfer rate is equal to the internal transfer rate minus whatever overhead the drive needs for transfer operations.

You'll sometimes see specifications that give a minimum, maximum, and average sustained transfer rate. The difference comes from the fact that the outer tracks of a disk platter have more data, so more data passes under the drive head during a single rotation when reading from the outside tracks than when reading from the inside tracks. The maximum sustained transfer rate is the transfer rate for the outer tracks. The minimum is the transfer rate for the inner tracks. The average is the average over the entire disk. Other factors that affect transfer rate include the density of the data on the disk and the speed of rotation.

Average Access vs. Average Seek (and Latency)

Access time tells you how long, on average, it takes the drive head to reach a designated spot on the disk. The faster the access time, the faster the drive will find a collection of small pieces of data, like a selection of records when you search a database or suggested alternatives for a misspelled word.

Access time consists of two components: seek and latency. Seek time is the amount of time it takes the drive head to move along the diameter of the disk to reach the right track. Latency is the amount of time it takes for the disk to rotate under the drive head to bring the right spot on the track under the head. The faster the rotation rate, the lower the latency. When you look at a drive's specifications, be sure you know whether you're looking at average seek time or average access time (sometimes seek is mislabeled as access time), and be careful not to compare the seek time from one drive to the access time of another.

Rotational Speed

The rotation rate tells you how fast the disk spins under the drive head. Typical rates for mainstream desktop drives are between 7,200 rpm and 10,000 rpm. High-performance drives often offer 15,000 rpm, and faster.

All other things being equal, the faster the rotation rate, the more data will move under the head in a given amount of time, the more data the head will read, and the higher the sustained throughput will be. However, rotation rates don't compare as neatly as they might, because all other things are not usually equal.

Rotation rate also affects average access time, because one of the two components of access time—latency—is determined by the amount of time it takes the disk to rotate the right spot on a track underneath the drive head after the drive head has reached the right track. The faster the rotation rate, the lower the latency, and the faster the access time.

Density

The density of data along a track, or linear density, obviously affects the capacity of a drive, because denser data means more data. Less obvious is that linear density affects performance. A drive with a higher linear density than an otherwise identical drive will have more data passing under the drive head with each rotation. That means the drive head can read more data in a given amount of time, and the drive will have a faster transfer rate. If one drive has a high enough density compared to another, it can have more data passing under the head even with a slower rotation rate; therefore, a high-density drive with a low rotation rate can have a faster transfer rate than a lower-density drive with a faster rotation rate. You'll rarely see the linear density specification for a drive, but you should keep this fact in mind when comparing rotation rates.

Interface

Internal drives for desktop systems come in many choices: IDE, SCS and SATAI. They all come in several variations. One of the key differences between one IDE or SCSI version and another is the transfer rate, with the interface transfer rate serving as the maximum rate, or burst rate, for the drive. Although adding a faster interface to a slow drive won't necessarily improve performance, a slow interface can slow performance down for a fast drive. Every time drive design improves to the point where the transfer rate at the drive head is in danger of catching up with interface transfer rate, the industry comes up with a newer, faster version of each interface, which is why there are several versions of hard drives.

Capacity

Capacity is obviously an important issue in picking a drive. In addition to getting enough capacity, however, you need to make sure your system can handle the drive capacity you get. The BIOSs in some older systems have a problem with any drive larger than 80GB. Some systems will recognize only 60GB of a larger drive. Other systems have similar capacity ceilings at 100GB, or some higher level. It's best to check with your system vendor beforehand to find out if there's a problem with the drive capacity you want. If there is, you may be able to fix the problem with a flash upgrade if your system uses a flash BIOS or even a simple download .exe file.

Form Factor

Form factor is just a way of describing how large a drive is and telling you what size drive bay you need. The vast majority of internal hard drives for the desktop are 3.5 inches. A few exceptions, typically including the largest capacity drives available, are half-height 3.5-inch drives. When you choose a drive, make sure you have an appropriate-size bay available for whatever drive you get. A 3.5-inch drive can fit in either a 3.5-inch or half-height 5.25-inch bay, but you may have to buy a separate mounting kit to install it in a 5.25-inch bay.

Related to form factor is the issue of internal versus external drives. The rule for choosing between the two is simple: Unless you have a good reason for getting an external drive—like not having a drive bay available—get an internal drive. It will save room on your desktop and typically save you $100 or more, because you won't have to pay for a external case. Consider an external drive if you don't have a drive bay available, want to move the drive between systems, or you want the convenience of plugging in the new drive without opening the case.

How Much Should I Spend?

Replacement or Additional Drive: $200 to $300

If you're looking for a state-of-the-art drive with good performance and high capacity, you should generally expect to spend a minimum of $200, with the actual price depending on the performance, capacity, and interface you want.

Extending the Life of an Old PC

If you're looking to extend the life of an old computer for another year or two, there's no reason to spend money on extra performance that an older computer probably can't take advantage of in any case. If at all possible you'll want to limit yourself to IDE drives with a top price of about $200. If you already have SATA or SCSI drives in your system, you should either consider limiting yourself to a relatively inexpensive, relatively low-capacity drive, or, if that's not possible, consider a state-of-the-art drive that you can move to your next system.

In this circumstance, the total cost of the drive will likely be more important than the cost per gigabyte. Even staying under $200, however, you can often get a lot more capacity for only a little more money, and lower the cost per gigabyte dramatically.

Shipping: $10 to $15

When you compare prices for drives from different vendors, don't forget to include the shipping cost. Hard drives are reasonably lightweight, so you won't find a lot of variation. You can generally expect a $10 to $15 charge

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What Do I Need to Install a New Drive?

Make Sure You Have a Drive Bay Available

Before you get an internal drive, take the cover off your system and make sure you have a bay available. Keep in mind that a 5.25-inch drive requires a 5.25-inch bay, but a 3.5-inch drive can fit in either a 3.5-inch or 5.25-inch bay. If you're planning to put a 3.5-inch drive in a 5.25-inch bay, however, you'll need a mounting kit to span the distance between the sides of the drive and the sides of the bay. If you need a mounting kit, be sure to order one with your drive.

SCSI Card for SCSI Drives

If you're getting a SCSI drive, make sure that you either already have an appropriate SCSI card in your system, or that you have a slot free for a card and that you get the card along with the drive.

Consider Possible File-System Limitations

If your BIOS can handle a larger capacity than 100GB, you can still use the entire drive by creating partitions of 30GB (or less), and letting your operating system treat each partition as a separate drive. If you're using Windows XP you have a choice of setting the drive to use a FAT or NTFS.

There are some benefits to partitioning your drive into several logical drives. You can use the partitions to help organize files, for instance reserving one logical drive for data, creating another for applications, and reserving drive C: for Windows and system utilities. Dividing your files this way also lets you easily maintain different backup schedules. For example, you may want to back up your data drive every day, your Windows and system-utilities drive once a week, and your programs drive only after installing a new program. Decide which approach you like before installing your new drive.

What Storage Alternatives Do I Have?

Removable Drives

Keep in mind that for some purposes you may be better off getting a removable drive rather than a hard drive. Among other advantages, a removable drive will let you change disks, giving you effectively unlimited storage space. Removable drives come in many variations. Capacities range from a mere 60GB to multiple gigabytes, prices range from under $100 to well over $1,000, and performance ranges from 7200 rpm to 15000 rpm hard drive, because some removable drives are actually standard hard drives mounted in removable cartridges. Some of the removable drives worth particular attention include CD-R and CD-RW drives, which let you write data to CDs that you can share with others, and DVDR+-RW+- drives, which offer essentially the same for DVD format.

Can I Upgrade the Drive in My Notebook?

Probably, But Check With the Manufacturer

Upgrading the hard drive in your notebook is a little different from upgrading one in a desktop system, mostly because you're limited to whatever the notebook supports. Chief among these limitations are form factor, number of drives, interface, and even specific disk capacities. Most notebooks, for example, can only accept 2.5-inch drives (though some take 3.5 inch drives), most are limited to only one drive, and, of course, they're limited to using whatever interface is built into the notebook. Even more limiting is that the BIOSs in many notebooks accept only those drives with specific, predefined parameters. Unlike most desktop BIOSs, you won't find a user-defined choice to let you set the number of cylinders, heads, and sectors per track to match the drive you want to install. If you want to replace your notebook hard drive, you should check with the notebook manufacturer to find out what choices you have, or should look for drives that specifically say they are meant for your model notebook.

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How Should I Pay?

Always Use a Credit Card

You don't forfeit your rights as a consumer if you pay by check, money order, check card, or debit card, but you forfeit the most practical way to enforce those rights—credit-card companies' clout—if there's a problem with the product or its delivery. Under the Fair Credit Billing Act, you have 60 days from the occurrence of the problem in which to report the details in writing. No credit-card company guarantees it will solve every problem or issue a chargeback for every disputed purchase, but the power of the creditor is often the heaviest weapon you can wield. Many debit cards now limit your liability to $50 in the event of fraud, but the money is already out of your checking account. It's the same with checks and even worse with money orders—they're the equivalent of cash.

Avoid Restocking Fees

It's the sometimes shocking reason you should always read the fine print: Restocking fees—often 15 to 20 percent of your total purchase price—can take a big bite out of a money-back return policy. Be sure to ask about the existence and terms of any restocking policies before you buy. Often, different restocking fees apply to different types of products or even to different parts of a system purchase. PC hardware, for instance, might be returnable without a restocking fee, but bundled software may be subject to a fee or nonreturnable once opened.

How Can I Choose A Reliable Brand?

Know Thy Warranty

All things being equal, a three-year warranty is obviously more attractive than a one-year warranty. But sometimes, a solid one-year plan—one that covers parts and labor on all components, not just some—can be better than three years of haggling and headaches. Ask questions like: Must you install replacement parts yourself? Who pays for return shipping for major repairs? Is a loaner unit available during downtime?

Ask Other Buyers

Advice from trusted colleagues is always a good recourse, as long as you keep in mind that a single person's experience with a company doesn't guarantee that yours will be the same.

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Interface	Technology	Transfer Rate		Cabling Connectivity	Connectivity
Interface	Technology	Current	Planned	Cabling Connectivity	Connectivity
ATA/IDE	- Parallel	- 133 MB/s	- At max today	- Wide ribbon - 40-pin - 18-inch length	- 2 drives per channel - Master/slave relationship - Shared bandwidth among drives
SATA	- Serial	- 150 MB/s	- 600 MB/s	- Thin, round ribbon - 4-pin - 1-meter length	- Single drive per channel - Point-to-point connection - Full bandwidth per drive
SCSI	- Parallel	- 320 MB/s	- None planned	- Wide, round ribbon - 68-pin - 12.5 meter (LVD) length	- Up to 15 devices per channel
SAS	- Serial	- 300 MB/s	- 1200 MB/s	- Thin, round ribbon - 6-meter length	- 128 devices - Expanders allow up to 16,000 devices

Features	Benefits
- High performance roadmap (1.5 to 6.0 gigabits/sec)	- Scalable performance growth
- Lowest-cost per megabyte	- Wide market appeal
- Command optimization	- Makes SATA RAID more practical
- Point-to-point connections	- Greater data reliability
- Full backward compatibility	- Easier, faster, cheaper migration
- Single thin 1-meter cable	- Greater flexibility; space savings
- Backplane connection Hot-plug/hot-swap flexibility	- Hot-plug/hot-swap flexibility

ATA	"Advanced Technology Attachment," a storage interface designed over 15 years ago and now the de facto I/O standard for desktop PCs. Though adequate for low data-demand applications, the combination of increased CPU capabilities, greater application through-put demands, and faster, more capable hard drives, severely limits the future usefulness of this interface.
Command Optimization	Commands to a device are queued for immediate execution, without having to wait for responses, increasing performance and making RAID more practical.
CRM	"Customer Resource Management" software.
IDE	"Integrated Device Electronics," the current low-cost storage interface standard for desktop and portable PCs, synonymous with ATA.
NAS	"Network Attached Storage," a storage design that connects a server to externally enclosed hard drives via a local area network.
OLTP	"Online Transaction Processing" database.
Parallel Technology	A design that allows a device (hard drive) to receive multiple bits of information at the same time. Parallel interfaces use short, wide cables carrying multiple signals, and pose inherent design limitations on data transfer speed and multiple device connections.
Point-to-Point	Direct connection between the backplane and the storage device, allowing for the high-performance, full utilization of bandwidth.
SAN	"Storage Area Network," a storage design that connects all the storage devices on a network with all the servers on a network for enhanced reliability and performance.
SAS	"Serial Attached SCSI," the serial imple-mentation of the SCSI standard, providing greater flexibility, performance, reliability, and connectivity.
SATA	"Serial ATA" is an evolutionary replacement for the Parallel ATA physical storage interface.
SCSI	"Small Computer System Interface," the predominant storage I/O technology for high-reliability, high-performance server applications.
Serial Technology	A design that allows data to be sent one bit at a time. Serial interfaces use thin cables, and are capable of faster speeds, greater reliability, and more flexibility in attaching multiple drives.