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|Computer Hardware Outline - Spring Week #13|
Solid State Hard Drives
What is a Solid State Drive-NAND Flash Memory
How SSDs Save data-Cell with two transistors
Advantages of SSDs
Speed, Long Life, Consumes Less Power, Quiet, Droppable
Disadvantages of SSDs
Expensive, Finite Number of Writes, Fail Without Warning
Hybrid Hard Drives
discrete SSD to hold the operating system and frequently used data, augmented by a more capacious conventional hard drive for less frequently accessed data and large collections of documents and digital media
SSDs vs. Hard Drives vs. Hybrids
Hard Drives-Magnetic Storage with Moving Parts
SSDs-Solid State Storage
Hybrids-Combination of Hard Drive and SSD
DIY Hybrids-Link Standard Hard Drive & SSD with Caching Software
3DGameMan Video on SSD
Newegg Solid State Drive
PC Assembly - Hard Drive
Online Documents How Solid State Drives Work
Hybrid Hard Drives
SSDs vs. Hard Drives vs. Hybrids
Homework - Wish List Hard Drive
How Solid-state Drives Work
by William Harris
Introduction to How Solid-state Drives Work
In 1956, IBM shipped the world's first hard disk drive, or HDD, in the RAMAC 305 system. The drive used 50 24-inch (61-centimeter) platters, stored a meager 5 megabytes of data and took up more room than two refrigerators. Oh, and the cost? Just $50,000 ($421,147 in 2012 dollars).
Since then, hard drives have grown smaller, more capacious and, thankfully, less expensive. For example, the Seagate Momentus laptop hard drive, with a form factor of just 2.5 inches (6.4 centimeters), offers 750 gigabytes of storage for less than $100. But even with advanced protection technologies, the Momentus drive, like all HDDs, can crash and burn, taking precious data with it. That's because hard drives have mechanical parts that can fail. Drop a laptop, and the read-write heads can touch the spinning platters. This almost always results in severe data loss.
Luckily, a new kind of computer drive could make crashes as obsolete as your Apple IIe. Known as a solid-state drive, or SSD, it uses semiconductor chips, not magnetic media, to store data. Your computer already comes with chips, of course. The motherboard contains some that house your device's system memory, or RAM, which is where information is stored and processed when your computer is running. Computer types refer to such memory as volatile memory because it evaporates as soon as your machine loses power. The chips used in a solid-state drive deliver non-volatile memory, meaning the data stays put even without power. SSD chips aren't located on the motherboard, either. They have their own home in another part of the computer. In fact, you could remove the hard drive of your laptop and replace it with a solid-state drive, without affecting any other essential components.
But why would you want to? And what exactly would the drive look like -- a green, printed circuit board or a brushed-metal box resembling a traditional hard drive? We'll answer those questions on the following pages, but before we give your machine a makeover, let's review a few computer science basics.
Memory Sticks and Thumbdrives
If flash memory sounds vaguely familiar, then you probably have at least one or two thumbdrives -- or memory sticks -- in your computer bag. The little devices, which have surprisingly large capacity and allow you to transfer data quickly between machines, are known officially as USB flash drives. They use the same NAND flash technology and, in many ways, can be thought of as the predecessors of today's solid-state storage devices.
What Is a Solid-state Drive?
In computer lingo, there's a difference between memory and storage. Random-access memory, or RAM (or simply memory), holds the program a computer is executing, as well as any data. Like a person's short-term memory, RAM is fleeting and requires power to do its job. Storage, on the other hand, holds all the stuff of your digital life -- apps, files, photos and music. It retains that stuff even if the power is switched off. Both RAM and storage boast their capacity based on the number of bytes they can hold. For a modern computer, RAM typically comes in 4, 6 or 8 gigabytes. Storage can have almost 100 times more capacity -- the hard drive of a typical laptop, for example, can hold 500 gigabytes.
Here's where it gets a little sticky. Some storage devices have what's referred to as flash memory, a confusing term that blurs the line between RAM and storage. Devices with flash memory still hold lots of info, and they do it whether the power's on or not. But unlike hard drives, which contain spinning platters and turntable-like arms bearing read-write heads, flash-memory devices have no mechanical parts. They're built from transistors and other components you'd find on a computer chip. As a result, they enjoy a label -- solid state -- reserved for devices that take advantage of semiconductor properties.
There are two types of flash memory: NOR and NAND. Both contain cells -- transistors -- in a grid, but the wiring between the cells differs. In NOR flash, the cells are wired in parallel. In NAND flash, the cells are wired in a series. Because NOR cells contain more wires, they're bigger and more complex. NAND cells require fewer wires and can be packed on a chip in greater density. As a result, NAND flash is less expensive, and it can read and write data much more rapidly. This makes NAND flash an ideal storage technology and explains why it's the predominant type of memory in solid-state drives. NOR flash is ideal for lower-density, high-speed, read-only applications, such as those in code-storage applications.
Armed with this background, we can offer a more precise definition of a solid-state drive: It's a device that uses NAND flash to provide non-volatile, rewritable memory. In computers, a solid-state drive can be used as a storage device, replacing the traditional hard disk drive. In fact, manufacturers produce SSDs with shapes and footprints that resemble HDDs so the two technologies can be used interchangeably. But that's where the similarities end. If you cracked open the shell of a solid-state drive, you wouldn't see platters and actuator arms. Let's do that next.
In this picture, it's easy to see this hard drive's platters, which look a bit like CDs stacked one on top of another, and an actuator arm.
How Solid-state Drives Save Data
On the outside, solid-state drives look just like HDDs. They're rectangular in shape, covered in a brushed-metal shell and sized to match industry-standard form factors for hard drives -- typically 2.5 and 3.5 inches (6.4 and 8.9 centimeters). But beneath the silver exterior, you'll find an array of chips organized on a board, with no magnetic or optical media in sight. Much of that stuff could fit into a smaller space, but SSD manufacturers dress up their components in extra "housing" to make sure they fit into existing drive slots of laptops and desktop PCs.
Compared to the stark simplicity of a solid-state drive, the innards of a hard drive are a marvel of motion, sound and activity. Round platters, arranged on a spindle, can spin at 7,200 revolutions per minute. An actuator arm, branching into multiple read-write heads, races across the platters in too-fast-to-be-seen bursts of speed. The arm connects to the actuator block, which holds the instructions for moving the read-write heads. As those instructions are called up, sometimes up to 50 times a second, the arm pivots at one end and moves the heads in unison over the platters. Once a head arrives at a certain location on a platter, an electromagnet produces a magnetic field, which aligns data-carrying domains in the underlying track. Each domain can be aligned in one of two possible directions -- 1 or 0. As these alignments change, they form patterns that correspond to discrete chunks of digital information.
The NAND flash of a solid-state drive stores data differently. Recall that NAND flash has transistors arranged in a grid with columns and rows. If a chain of transistors conducts current, it has the value of 1. If it doesn't conduct current, it's 0. At first, all transistors are set to 1. But when a save operation begins, current is blocked to some transistors, turning them to 0. This occurs because of how transistors are arranged. At each intersection of column and row, two transistors form a cell. One of the transistors is known as a control gate, the other as a floating gate. When current reaches the control gate, electrons flow onto the floating gate, creating a net positive charge that interrupts current flow. By applying precise voltages to the transistors, a unique pattern of 1s and 0s emerges.
NAND flash comes in two flavors based on how many 1s and 0s can be stored in each cell. Single-level cell (SLC) NAND stores one bit -- either a 1 or a 0 -- per cell. Multi-level cell (MLC) NAND stores two bits per cell. MLC flash delivers higher capacity, but it wears out more quickly (yes, wears out -- we'll cover that more in a couple of pages). Still, it's less expensive per gigabyte than SLC and, as a result, is the preferred technology in almost all consumer-level SSDs.
Cost has been one of the biggest hurdles of flash memory and, consequently, of solid-state drives. But in recent years, costs have dropped significantly. At the same time, advances in NAND flash development have taken what's good about the technology and made it even better. Up next, we'll look at the advantages of solid-state drives.
This 480-gigabyte solid-state drive made by SanDisk was retailing for $372.91 (on sale) when we last checked on Amazon. List price was $699.99.
Sold on SSDs: Advantages of Solid-state Drives
You've invested in a top-of-the-line laptop with a 500-gigabyte hard drive, and it's working great. You've got all your photos and videos, your entire music library, five half-finished novels and applications galore packed onto the drive's platters. Why would you consider swapping the HDD for a solid-state drive? Didn't Dad always say, "If it ain't broke, don't fix it"?
Maybe Dad didn't own any hard drives. The harsh reality is that HDDs can and do fail, often more frequently than their technical specs would seem to suggest. For example, hard drive manufacturers rate the reliability of their products using a measurement known as mean time between failures, or MTBF. A typical consumer hard drive has a MTBF rating of 500,000 hours, meaning that, in a sample of drives tested, there would be one failure every 500,000 hours of testing. That's one failure every 57 years, which sounds pretty good, right? Unfortunately, MTBF scores are misleading. They come from a statistical evaluation based on a small sample size and a short amount of time. In reality, you'd also want to consider a typical HDD's warranty and service life (three to five years or so), along with the MTBF score. Because they have no moving parts, SSDs can deliver improved reliability. They can rate up to 2.5 million hours MTBF, which probably means a few more years added to the lifespan of the device.
An even bigger deal is the performance of solid-state drives compared to HDDs. With no moving heads and spinning platters, SSDs can access one piece of data as quickly as any other piece, even if they aren't in the same proximity. The speediness of the device manifests itself in all key CPU tasks, from booting up system software to opening files to reading and writing data. The following bullets compare SSDs and HDDs on these critical activities:
Boot-up time (Windows 7): 22 seconds (SSD), 40 seconds (HDD)
Data read-write speed: 510-550 megabytes per second (SSD), 50-150 megabytes per second (HDD)
Excel file open speed: 4 seconds (SSD), 14 seconds (HDD)
All of this adds up. Even a casual user will notice a significant increase in the performance of a computer equipped with an SSD. But a power user will really feel the difference. Game designers, animators and other folks rendering huge output files were early adopters of SSDs just because of the cumulative time they could save reading and writing large files. Today, gamers, photographers and anyone editing graphics or video files will appreciate the boost in speed a solid-state drive delivers.
Finally, SSDs consume far less power than traditional hard drives, which means they preserve battery life and stay cooler. They're also super quiet, with none of the whirring and clicking you get with HDDs. You'll appreciate this more if you're a frequent traveler and often have your computer perched on your knees, but even if your laptop remains docked most of the time, a cooler, quieter machine can make a noticeable difference in the comfort of your workspace.
Of course, no technology is perfect, and SSDs are far from it. On the next page, we'll examine the negatives of NAND flash and why a combination of technologies may be the best solution.
Not Sold on SSDs: Disadvantages of Solid-state Drives
Trading out your hard drive for a solid-state drive seems like a no-brainer. But before you make the switch, you should understand the limitations of SSDs. Like cost. Even though prices have decreased steadily, NAND flash memory is still expensive. To get 240 gigabytes of storage on a PNY Prevail SSD, for example, you might shell out $280. That's $1.17 per gigabyte. The Western Digital Scorpio Blue HDD, on the other hand, gives you 250 gigabytes of storage for roughly $65. That works out to be $0.26 per gigabyte.
Then there's the issue of longevity. The NAND flash used in SSDs can only be used for a finite number of writes. Why? Because SSDs can't write a single bit of information without first erasing and then rewriting very large blocks of data at one time. Each time a cell goes through an erase cycle, some charge is left in the floating-gate transistor, which changes its resistance. As the resistance builds, the amount of current required to change the gate increases. Eventually, the gate can't be flipped at all, rendering it useless. This decaying process doesn't affect the read capabilities of SSD, because reading only requires checking, not changing, the voltages of cells. As a result, NAND flash can "rot" into a read-only state.
Some manufacturers use something called wear-leveling to counteract the degradation of NAND flash. This technique distributes data writes across all blocks to make sure the flash memory wears evenly, but even with that, SSDs will decay over time. NAND flash memory of the single-level cell variety generally delivers 50,000 program/erase cycles. Flash of the multi-level cell variety -- the kind used in consumer-level products -- wears out after about 5,000 cycles.
For this reason, many data centers and techies use a combination of SSD and HDD. One approach is to use a solid-state drive in a laptop and a traditional hard drive as external storage holding music, photos and other files. This combines the best of both worlds -- the ultrafast, random data access of SSD with the relatively inexpensive, high capacity of HDD. If this sounds good to you, you'll want to start shopping for a suitable solid-state drive. Leading manufacturers include Samsung, Seagate, SanDisk, PNY, Toshiba and OCZ Technology. And don't forget about Intel, which offers a robust line of drives, as well as several tools to help you choose the right technology and calculate how much time and money you can save if you make the switch to SSD.
Hybrid hard drives: How they work and why they matter
An SSD can read and write data many times faster than the best mechanical hard drive. On the downside, flash memory is many times more expensive than the innards of a typical hard drive, so manufacturers have limited their SSD capacities to hit reasonable price points: A 128GB SSD costs about $130, and for that same price tag, you can buy a 3.5-inch desktop hard drive that delivers 2TB of storage, or a 2.5-inch laptop drive that provides 1TB of storage.
Two years ago, Seagate (quickly followed by Samsung) introduced a drive that married a small SSD with a mechanical drive. The objective was to deliver the superior speed of an expensive SSD, while retaining the higher capacity and lower cost of a conventional hard drive. Now that Toshiba and Western Digital are joining the party, it's a great time to explain in more detail what hybrid drives are and how they operate.
Hybrid drives work much in the same way as the current dual-technology configurations in many gaming and power-user PCs, as well as some ultraportable laptops. Such systems have a small, discrete SSD to hold the operating system and frequently used data, augmented by a more capacious conventional hard drive for less frequently accessed data and large collections of documents and digital media.
Current hybrid drive designs, in contrast, deliver both technologies within a single physical unit, and they employ software caching algorithms (rather than relying on the user's brain) to decide which data belongs on the SSD portion and what goes on the drive’s platters.
These caching algorithms reside in the hybrid drive's firmware, not the device driver. To the computer’s operating system, a hybrid drive appears as a single unit with the SSD portion acting strictly as a large cache. The cache is nonvolatile, so the data doesn't disappear when power is absent.
You can find several hybrid designs on the market, but the most common is a 2.5-inch version meant for laptops, Seagate's Momentus XT SSHD. Seagate refers to the caching logic it uses on the Momentus XT drives as Adaptive Memory technology. The thinner 7mm, 2.5-inch drives that Toshiba and Western Digital recently announced are destined for Ultrabooks. They will likely use similar technologies with similarly suitable names, although either company might opt to skip caching and produce a dual SSD/hard drive in a single physical package.
In any case, a caching algorithm will track the files you load the most often (operating system files, applications, and the like), and store them on the SSD portion of the drive. From that point on, these files will load into memory much faster than they did from the mechanical drive, although some overhead will be involved as the computer determines whether the file in question resides on the SSD. No caching will have occurred the first time you use a hybrid drive, so its initial performance will be the same as that of a mechanical hard drive, but the speed will increase over time.
To test a current implementation and to determine how much improvement you can expect over the long term, we ran a special version of WorldBench 7 six times using a 750GB Seagate Momentus XT hybrid drive with its 8GB internal SSD.
The WorldBench 7 score for Seagate's Momentus XT hybrid drive indicates that it's a little faster than a conventional hard drive, but much slower than a true SSD.
Over the course of the six runs, system boot times dropped from 35 seconds to 31 seconds, and the WorldBench 7 score rose from 112 to 116. That's about a 12 percent improvement in boot times, and a 4 percent jump in WorldBench. However, the WorldBench 7 score of a nonhybrid, 5400-rpm drive also climbed by 4 percent—most likely due to Windows 7's own caching technologies. The standard drive showed no decrease in boot times, so the current Seagate hybrid drives do offer some benefit.
WorldBench 7 measures application performance, not the load times of the applications themselves, though subjectively the load times seemed only slightly faster after the first pass in my hands-on tests when I eliminated the Windows prefetch and swap file. Let's call that further, marginal evidence that a hybrid can make a positive difference in your everyday computing. Just for comparison's sake, a good SSD scored more than 40 points higher on WorldBench 7 on the same system.
The specs for the upcoming Toshiba and Western Digital hybrid drives weren't available at the time of this writing; however, you might see models with 16GB or even 32GB SSD portions that provide a greater increase in performance. The larger the SSD in the hybrid drive, the more data you can cache and the less often you'll need to load data from the hybrid’s slower mechanical drive. Integration and interaction with operating systems could also boost hybrid performance, assuming of course that a significant drop in SSD prices doesn't render the technology moot.
As of October 10, 2012, a standard 750GB, 2.5-inch hard drive was about $80, a 750GB Momentus XT SSHD was about $130, and a brand-name 128GB SSD also cost about $130. Given those prices, current hybrid drives really make sense only in laptops, and only when you want high performance and more storage capacity than an SSD can provide.
In a desktop PC with unoccupied drive bays, you'll get much better bang for your buck with a stand-alone SSD combined with one or more mechanical hard drives. Even for a laptop, a smaller, more affordable SSD supplemented by an external conventional hard drive might better deliver the performance and the capacity you're looking for.
SSDs vs. hard drives vs. hybrids: Which storage tech is right for you?
In times past, choosing the best PC storage option required merely selecting the highest-capacity hard drive one could afford. If only life were still so simple! The fairly recent rise of solid-state drives and hybrid drives (which mix standard hard drives with solid-state memory) have significantly altered the storage landscape, creating a cornucopia of confusing options for the everyday consumer.
Yes, selecting the best drive type for a particular need can be befuddling, but fear not: We’re here to help. Below, we explain the basic advantages and drawbacks for each of the most popular PC storage options available today. Tuck away this knowledge to make a fully informed decision the next time you're shopping for additional drive space.
Hard-disk drives have been the default storage component in desktop and laptop PCs for decades. As a result, the term "hard drive" is now the common descriptor for all storage hardware—the digital equivalent of "Q-Tip" or "Band-Aid." Although modern hard-disk drives are far more advanced and higher-performing than their counterparts from yesteryear, on many levels their basic underlying technology remains unchanged. All hard-disk drives consist of quickly rotating magnetic platters paired with read/write heads that travel over the platters’ surfaces to retrieve or record data.
HDD interiors almost resemble a high-tech record player.
The technology is mature, reliable, and relatively inexpensive compared with other storage options; most hard-disk drives can be had for only a few cents per gigabyte. Hard-disk drives are available in relatively high capacities too, with today’s largest drives storing up to 4TB of data. Usually hard drives connect to a system via the ubiquitous SATA (Serial ATA) interface, and they don’t require any special software to work properly with current operating systems.
In other words, traditional hard drives are spacious, simple, and comparatively dirt-cheap.
Hard-disk drives don’t perform nearly as well as solid-state drives or even hybrid products do in most situations, however. Today’s fastest hard drives can read and write data at more than 200MB per second with sub-8ms access times, but those numbers are significantly worse than the speeds of even some of the most affordable solid-state drives (which I'll cover in a bit). The faster the platter rotation speed, the faster the hard drive. For example, a 7200-rpm drive outperforms a 5400-rpm drive.
Hard-disk drives are best suited to users who need vast amounts of storage and aren’t as concerned about achieving peak system performance. If you're an everyday PC user who sticks mostly to email, Web browsing, and basic document editing, a standard hard drive should suit you fine. Just don't tinker around with someone else's SSD-powered PC, because once you've gotten a taste of a solid-state drive's blazing read/write speeds, it's hard to go back to even the speediest of traditional hard drives.
Several manufacturers offer SSDs. The HDD market is much more condensed.
On many levels, solid-state drives are similar to hard drives. They usually connect to a system by way of the SATA interface (though PCI Express-based drives are also available for ultrahigh-performance applications), and they store files just as any other drive does. SSDs, however, eschew the magnetic platters and read/write heads of hard-disk drives in favor of nonvolatile NAND flash memory, so no mechanical parts or magnetic bits are involved.
By ditching the relative slothfulness of moving parts, solid-state drives deliver much better performance. They're the fastest storage option available. And not only can SSDs read and write data much faster than hard drives with most workloads, but they can also access the data much more quickly as well.
Whereas the fastest hard drives can read and write data at about 200MB per second and access data in a few milliseconds, the fastest solid-state drives can achieve 550-MBps (or higher) transfers that essentially saturate the SATA interface, and their typical access times are a fraction of a single millisecond. In a nutshell, SSDs make for a much snappier, much more responsive system, with lightning-fast boot times, application launch times, and file-transfer speeds.
Another huge SSD advantage is durability. Because they have no moving parts, solid-state drives aren’t susceptible to damage or degraded performance from vibrations or movement. Drop a system or laptop containing a traditional hard-disk drive, and you have a very real chance of corrupting your data. But a solid-state drive won’t—can't—skip a beat.
Solid-state drives aren't without disadvantages, though. For one, SSDs are much more expensive than hard drives in terms of cost per gigabyte. Good, consumer-class solid-state drives run about $0.70 to $1.00 per gigabyte, whereas hard drives cost only a few cents per gigabyte. Solid-state drives don’t offer anything near the capacity of hard drives, either: The most popular SSDs have capacities of about 120GB to 256GB, with 512GB to 1TB models reserved only for those with gargantuan budgets.
OCZ's Vector SSD is one of the fastest around.
SSD performance also varies depending on how full the drive is, or if it has been purged of data. Idle garbage collection or a feature called TRIM can help restore the performance of a “dirty” SSD, but that requires driver and OS support. (Windows 7 and 8 support TRIM.) Because the capacity is relatively small and performance is affected by how full the drive may be, many SSD users find themselves regularly moving less-performance-intensive data (such as documents or media collections) off their solid-state drives and onto traditional hard drives.
Another concern: When SSDs fail, they tend to do so without warning. Hard drives, however, will usually start to show signs of failure by throwing a S.M.A.R.T. error or suffering from a few bad blocks. In our experience, SSDs simply die without waving many—if any—red flags.
Solid-state drives are best suited to savvy PC users who seek high performance. If you don’t mind managing multiple volumes and you have the budget, pairing a fast SSD with a high-capacity hard drive will result in the best of both worlds. The SSD can hold the OS and your most frequently used applications, while the hard drive can handle the bulk-storage duties. Managing multiple storage volumes can be a bit of a pain for casual PC users; if you know your way around a PC, however, combining a fast SSD and large hard-drive storage is a great, high-performance approach with minimal compromise.
Hybrid hard drives
Seagate Hybrid drives such as the Momentus XT offer the best of both worlds, but fulfill that promise only to a certain extent.
Hybrid hard drives blend HDD capacity with SSD speeds by placing traditional rotating platters and a small amount of high-speed flash memory on a single drive.
Hybrid storage products monitor the data being read from the hard drive, and cache the most frequently accessed bits to the high-speed NAND flash memory. The data stored on the NAND will change over time, but once the most frequently accessed bits of data are stored on the flash memory, they will be served from the flash, resulting in SSD-like performance for your most-used files.
Some of the advantages of hybrid storage products include cost, capacity, and manageability. Because only a relatively small solid-state volume is required to achieve significant performance gains, a large investment in a high-capacity SSD isn’t necessary. Hybrid drives tend to cost slightly more than traditional hard drives, but far less than solid-state drives. And because the cache volume is essentially hidden from the OS, users aren’t required to cherry-pick the data to store on the SSD to prevent it from filling up. The hybrid storage volume can be as big as the hard drive being used, and can serve as a standard hard drive. Boot times also see some improvement.
The OCZ RevoDrive Hybrid.
Where hybrid products falter is with new data. When writing new data or accessing infrequently used bits, hybrid products perform just like a standard hard drive, and new hybrid drives have a "break-in period" while the software learns which data to cache. Due to the fact that hybrid products rely on caching software, they can also be somewhat more difficult to configure.
For users who don’t want the responsibility of managing multiple volumes or who don’t constantly work with new data, a hybrid drive can be a great option to improve system performance—all without having to give up any capacity or having to deal with the headaches of using separate solid-state and hard-disk drives.
DIY hybrid storage configurations
That being said, some people create DIY hybrid storage configurations by linking a standard hard drive and an SSD with specialized caching software. (This is not the same as simply plopping both an SSD and an HDD into your PC.) Solid-state cache drives often ship with proprietary caching software included, though you can also take advantage of Intel's Smart Response Technology if you want to use an SSD that isn't specifically marketed as a cache drive.
Functionally, the setup performs the same as a typical hybrid drive, though stand-alone SSD caches often come in larger capacities than the paltry flash storage you'll find on most self-contained hybrid drives—meaning more of your data will receive an SSD-powered speed boost. On the other hand, you'll have to buy both a hard-disk drive and a solid-state drive, which can get pricey. You'll also need to configure the setup manually, whereas self-contained hybrid drives are much more of a plug-and-play option.