 |
|  shopping cart  my account  log in |
low prices in Electronics, Books, Music, DVDs & more
|
|
| Electronics Superstore: Buying GuidesBuy New & Used Electronics at Halfvalue's Electronics SuperstoreBuy Electronics at Halfvalue's Electronics Superstore. Find thousands of new and used Electronics at cheap prices from hundreds of online sellers and dozens of bookstores all over the internet. Our Electronics Superstore is your source of cheap new and used Electronics. Buy and sell cheap used and new books & Electronics at our marketplace and see for your self how easy it is to make money and save money online with Halfvalue.com! |
Hard Drive Buying GuideBuyers' Guide to Hard Drive Contents
------------------------------------------------------------------------------------ Every PC has at least one -- many have more than one. Camcorders, video recorders MP3 players and even digital cameras now have them. The hard disk is one of the most important parts of a PC. It provides permanent, large-scale storage in the PC, retaining information even when the PC is powered off (unlike the memory). It's where the operating system, programs and documents on your PC are stored permanently. If you're buying or building a new PC, or have simply run out of space on your existing PC and need to boost your storage capacity, knowing what to look for in a hard disk is vital. Originally conceived in the 1950s, a hard disk comprises of one or more circular platters of magnetic material, with billions of microscopic magnetic domains, each representing one bit of data. These zones are embedded into concentric circles, called tracks. A read/write head floats above the tracks, and the magnetic flux patterns of the zones affects an electric current flowing through the head, which in turn registers as a "0" or a "1" to the drive's electronics. The head can also alter the magnetic patterns, to write data onto the disk. When in operation, an electric motor spins the hard disk constantly, rather like an LP or CD, in order to bring the data on the tracks around to the head. The head moves across the surface of the disk, to position it above the track on which the desired data is stored. The head will then wait for the rotation of the disk to bring the data around. A "hard disk", as we understand it today, will usually comprise multiple platters (typically three in a standard consumer hard disk), packaged in a standard-size casing. Desktop hard disks for instance, are usually packaged to go into 3.5in slots in your computer case. For most users, the most important feature of a hard disk is how much data it can store. Recently released hard disks can store up to 400GB on a single 3.5in disk. Most people don't need that much space, however, and more mainstream disks tend to float around the 120GB-200GB mark. The going rate for capacity tends to be around $1 per gigabyte, with significant variation for premium and ultra-high capacity products. The planned use of a PC's hard disk will determine how much space is required. In consumer PCs, much of the space on a PC's hard disk will be consumed by media files. If you plan to store a lot of media - especially video, but also audio - you need a big hard disk (especially if you plan to leave the media on the hard disk permanently, rather than archive it to DVD or tape). The following list should give you a rough estimate of the amount of space each application will take on a hard disk.
One constant source of confusion for buyers of hard disks is the disparity between the advertised size of the hard disk and the capacity that is reported by the operating system. More than one buyer has felt ripped-off when they installed their shiny new 80GB hard disk, for instance, only to find that the operating system tells them that the disk only has a 74.5GB capacity. This is not actually an error, but an holdover of the different ways in which the hard drive vendors and the software systems measure capacity. When calculating their disk size, hard drive vendors use the decimal definition of gigabyte. That is, one gigabyte equals 1000 megabytes; one megabyte equals 1000 kilobytes and so on. The operating system, however, will use the binary definition of a gigabyte when calculating available space. In binary terms, one gigabyte equals 2^10, or 1024 megabytes. One megabyte is 1024 kilobytes. So, using a decimal definition (as the hard drive vendors do, for obvious reasons), a hard disk with 80,000,000,000 bytes of storage is 80GB. But in binary terms, that's a little less than 75GB. The other primary specification to look for when choosing a hard disk is the interface. The interface is the way in which the hard disk communicates with the rest of the computer - if you like, the kind of plug and cable system that it uses to connect with the other components of a PC. The most common types of hard disk interface are parallel advanced technology attachment (PATA, also called IDE or EIDE), and Serial ATA (SATA). External hard disks will likely have a USB or FireWire interface. Whichever you choose, it must be an interface that your PC supports. One important thing to realise is that the speed of an interface is not the same thing as the speed of a hard disk. The speed of an interface describes the theoretical transmission capacity of the interface itself. For instance, SATA is capable of 1.5Gbps, which means that it will support transfers from the hard disk of up to 1.5Gbps. You'll never find a hard disk that can actually fill that capacity, however - most will likely have a peak transfer rate of around 50-70MBps. The EIDE interface, known retrospectively as Parallel ATA, is slowly being phased out in favour of SATA. It's still found in nearly all PC's however. The nomenclature can be a little confusing. You'll often see parallel ATA ports on motherboards and hard disks described as ATA133, Ultra DMA133, Ultra ATA133 or something similar. In this context, "ATA", "Ultra DMA" and "Ultra ATA" mean the same thing. The number in the above names actually describes the speed of the interface. ATA133, for instance, tells you that the maximum transfer rate of the interface is 133MBps. A motherboard that only supports ATA100 has a transfer rate capacity of 100MBps. Older motherboards will support slower speeds. Some old motherboards will only support ATA66, for instance. Most commonly, you will find motherboards that support ATA33, ATA66, ATA100 and ATA133. All of these are PATA standards. You can, to a certain extent, mix and match motherboard specifications with hard disk specifications. For instance, you can plug an ATA133 drive into a motherboard that only has support for ATA100. The interface will only operate at 100MBps, but the drive should work just fine. The same is true in reverse - an ATA100 drive plugged into an ATA133 port will work, but at the slower rate. The exception is the old ATA33 standard, which uses a different kind of cable to ATA66 and above. It uses a 40-wire cable, rather than an 80-wire one. (As an aside, you can plug ATA66 and faster hard drives into the motherboard using a 40-wire cable, but they will only run at 33MBps). Parallel ATA uses broad "ribbon" cables. Each cable will have two plugs on it, because each PATA port supports up to two drives (be they hard disks or optical drives). That is, each EIDE port on the motherboard supports two drives, chained on the same cable. If you do put two drives on a single port, you need to set one as "master" and one as "slave", which requires physically moving jumpers (small connectors) on the hard disk. The hard disk manual will tell you what jumper settings to use. An EIDE port will only operate at the speed of the slowest device connected.  Serial ATA was designed to improve the transfer speeds of hard disks as well as eliminate some of the uglier aspects of PATA. It is the successor to PATA, but currently co-exists with it on most motherboards during the "phase-in" period. Most motherboards you buy today will have both PATA and SATA ports, so you can choose to attach your preferred type of hard disk. SATA, in its most common implementation, SATA150 (usually just called SATA) has a potential speed of 150MBps, faster than the fastest PATA interface (133MBps). If you're planning to build your own PC, you'll also appreciate some of SATA's other advantages. It uses a much smaller cable than PATA, making the PC's interior cabling much easier to manage. It also works on a one-port, one-device basis, so you don't need to worry about master/slave relationships. Also, the cables are universally keyed, so there's no danger of inserting cables upside down (which was a big problem with old PATA disks). SATA is better in every way to PATA, and is recommended in preference to PATA if your PC supports it. There is still a slight premium for SATA hard disks, however, although this premium has dropped to $5-$10 on most drives. Recently, we've started seeing the first iterations SATA2 appear on the market in both motherboards and hard disks, although it is still very rare. SATA2 has a potential speed of 300MBps, twice that of SATA (although we've yet to see a hard disk that can max-out SATA), and several other new features - including improved support for hot-plugging (that is, plugging drives in while the PC is still running) and external ports, allowing you to use external SATA2 hard disks. SATA2 also supports native command queuing (see later) and is backwards compatible with SATA.  Although not really appropriate for consumer applications, the SCSI (pronounced "scuzzy") interface bears mentioning. With SCSI, up to 15 devices can be daisy chained to a single port. Its latest iteration, Ultra320, supports speeds of up to 320MBps per port. SCSI is typically used in servers and for applications where support for a very large number of hard disks is required. The reason it's not really appropriate for consumers is, purely and simply, its heavy cost. SCSI hard disks cost vastly more than PATA or SATA disks, and you won't find a SCSI interface on any PCs or motherboards targeted at consumers. If you want SCSI, you'll need to buy an interface board for your PC. The common external interface for plugging in peripherals like mice and printers can also be used to plug in hard disks. Drives with a USB interface are always external drives, designed to act as portable, high-volume storage. You can plug a USB drive into a running Windows XP or MacOS PC, and it will automatically and immediately appear as an available drive. USB 2.0 has a theoretical transfer rate of up to 480Mbps, which is more than enough to support very fast transfers to and from the external hard disk. USB 2.0 also carries a limited amount of power, so many external USB 2.0 hard disks (generally speaking, the smaller ones) require no mains power and can draw all they need from the USB port. Some USB drives will use two USB ports, the second one usually as an additional power source. Because USB 2.0 is backwards compatible, it is possible to plug USB hard drives into older PCs that only support USB 1.1. USB 1.1 is very slow, however - only 11MBps - and will make accessing data on the hard disk extremely slow. Much like USB 2.0, FireWire (also known as IEEE1394) provides an external high-speed port into which you can plug hard disks. Most new PCs now ship with FireWire, but a FireWire expansion card can be readily bought for less than $50. In its most common iteration, FireWire operates at 400Mbps, slightly slower than USB 2.0. Tests have shown that, in spite of being slightly slower than USB, FireWire is actually a more efficient carrier of high-volume data, and is often preferable to USB as a hard disk interface. A new FireWire standard that supports 800MBps has recently appeared also. Much like USB, FireWire also carries a limited amount of power, and can power small external drives without the need for plugging into mains power (which is very useful if you're a notebook user). The introduction of SATA has changed the way that internal hard drives are connected to the PCs power supply. PATA and older drive use the standard Molex connector for plugging the power supply into the hard drive (the Molex connector is the standard white power connector). Most SATA drives use a different type of connector, however, designed specifically for SATA to make is more amenable to hot-plugging. Many new power supplies will have SATA power connector built-in, and if you have an older power supply a Molex to SATA power adapter can generally be purchased for less than $10. If you have an external hard disk, it is possible that the interface (FireWire or USB) itself carries enough power to drive the motor. If not, you will need to connect the drive directly to mains power. If the drive does require main power, the power cable will be supplied with the drive. Typically, internal PC drives come in the 3.5in form factor, which means that it is designed to fit in the same size slot as a 3.5in floppy drive. There are other drive sizes, however, designed to go into different devices. The next most common size for hard drives is the 2.5in size. These are considerably smaller and lighter than 3.5in drives (but also slower and with less capacity). Typically, 2.5in drives are designed to go into notebook computers, but it is becoming more common for them to be sold at retail for use as external drives because of their low power requirements and light weight. A single USB or FireWire port is often enough to power a 2.5in drive, obviating the need for mains power. You won't find them at retail, but 1.8in drives are being manufactured in increasing numbers. They're used by equipment manufacturers as very portable storage solutions, especially in MP3 players like the iPod. Some notebook manufacturers are also using 1.8in drives in slimline products. There are also Microdrives from Hitachi, IBM and Seagate. These are very small drives - little larger than postage stamps - that slot into Type II CompactFlash flash memory slots. With capacities up to 4GB presently, these drives are designed for use in digital cameras, MP3 players and video cameras.  External hard disks are becoming increasingly popular as a means of transferring huge amounts of data between PCs. Typically, they plug into the PC's USB or FireWire port (some support both) and will instantly appear in a file manager such as Windows Explorer as an additional drive. Copying to and from the drive is a simple matter of dragging and dropping. The entire external hard disk can then be unplugged, carried to another PC, and the files copied off it. Neither FireWire nor USB can match the performance and efficiency of the internal standards (PATA, SATA and SCSI), however, and while it is possible (if the motherboard supports it) to use an external drive as the PC's primary drive, it is not recommended. The new SATA2 standard supports an external connector that will allow external drive performance to match that of internal drives. SATA2 does not support any power carriage, however, so external SATA2 drives will need to find a power outlet nearby. External drives are most often packaged (that is you buy an entire unit, including the drive and the connectors), but relatively inexpensive bridging devices can also be bought that allow you to plug a commodity internal hard disk into the outside of the computer. These are devices that plug into your PC's FireWire or USB port. You can then plug a commodity internal hard disk, that you have bought separately, into the device. The internal hard disk then effectively becomes an external USB or FireWire device. The external hard disk connectors are available for either 3.5in or 2.5in drives, and can be either USB or FireWire. They usually rely on mains power to drive the hard disks. You can also buy drive caddies, which are removable hard disk trays that allow you to put a commodity internal hard disk into it and slide the caddy/drive in and out of the PC like a desk drawer. Note: Presently, external USB 2.0 and FireWire cases are currently only available for PATA hard drive and not SATA. There are currently no USB 2.0 and FireWire bridge chips for SATA drives. Other hard disk specifications There are lots of other things that hard drive manufacturers will tell you about their drives, apart from the capacity and interface. The most commonly mentioned is the rpm, but MTBF (mean time between failures), access times and noise levels are also important characteristics of hard disks. The most often quoted specification, apart from the capacity of the hard disk and how it connects to the PC, is the revolutions per minute (rpm) supported by the drive motor. This is a very important component of drive performance - the faster the drive platters spin, the faster they carry data to the read head. All other things being equal, a 7200rpm drive should be able to stream data off a platter 33 per cent faster than a 5400rpm drive. The rpm is also a key component of a drive's access time, which we'll go into in a moment. The lion's share of consumer hard drives available now are 7200rpm, but some older drives are still available that run at 5400rpm. Faster drives, with 10,000rpm and even 15,000rpm motors can be purchased also. Drives with 10,000 or more rpm tend to be considerably more expensive and have much smaller data capacities than 7200rpm drives. In some case, a drive's access time is an important indicator of performance as its rpm. The access time is the amount of time it takes to start reading a given piece of data. It incorporates the amount of time it takes for the drive to move the head over the track on which the desired data is stored (the "seek time") and the amount of time it takes for the rotation of the disk to carry the part of the track on which the data is stored around to the head (the "latency"). The average seek time plus the average latency, will give you an indication of the average access time of the hard disk. Hard disk manufacturers will usually tell you the average seek time for the specific model of hard disk, although sometimes you have to go digging for the information. Typically, seek times are in the range of 8-10 milliseconds (ms). The latency is entirely a function of the drive's rpm. The faster the spin, the faster the data comes around. A 7200rpm drive has a latency of 4.2ms. A 10,000rpm drive - 2.99ms. Access times are important, especially if the hard disk has to access lots of small or fragmented files, scattered around the physical space of the platter. Often it will take longer for the hard disk to get the head in position to read the data than it will to actually do the reading. A new feature of hard disks, native command queuing is available in a number of SATA2 hard disks and is supported by several new motherboard chipsets, including the Intel 955 and NVIDIA nForce4. Native command queuing is a kind of buffering system, designed to minimise the movement of the hard drive's head, and thus reduce the access times. Native command queuing will dynamically re-order data fetch instructions in order to maximise the efficiency of the hard disk. Say the computer asked for some data that was on track 20, then some data on track 300, than some data on track 30. A normal (non-NCQ) hard disk would do these sequentially, moving the head from one side of the disk to the other. A hard disk with NCQ, working with a supporting chipset, would instead execute operation three ahead of operation two, to save the head from travelling all the way across to track 300 and then back again. It's hard to quantify the speed improvement that NCQ provides, since it largely depends on the conditions. According to hard drive vendor Seagate, it can, under the right circumstances, provide an overall speed boost of 30 per cent or more. In spite of years of ridicule, hard drive vendors still often quote mean time between (or to) failure (MTBF, or sometimes MTTF) as a measure of hard drive reliability. MTBF is meant to describe the mean time it takes for an error to occur in a hard drive model's operation. Because of the way the vendors calculate it, MTBF is a largely useless measure. Figures in excess of 1,000,000 hours are commonly quoted, which would lead many to believe that the hard disks, on average would last a million hours or more before breaking down. That's not the case (if you do the math, a million hours is over 114 years!). We suggest you ignore MTBF ratings. Noise ratings are rarely quoted, but are becoming more important as we see more external hard disks in use, as well as hard disks going into devices that are sensitive to noise and vibration. Hard drive acoustics measurement can become quite complicated, but most hard drive vendors rate their hard drive acoustics by decibel. A very quiet drive will have a peak sound output of less than 25dB. This is about the point at which humans can discern sound, making a drive with less than 25dB effectively noiseless. Hard disk performance and getting the right drive for you The ultimate performance of a hard disk is determined by many factors, including some that are unknowable by the end user. The interface, the rpm and the seek times are the best indicators that we, as consumers, have of the speed of a hard disk. Several X factors also apply: the quality of the drive electronics, the density of the magnetic zones (the "areal density" - the more dense the zones, the more data is carried past the head with each revolution), the number of platters and so forth. It's often hard to tell how fast a drive is without proper benchmarking, so we recommend checking out Web reviews of hard disks. Buying the correct drive for you is largely a matter of whether you value speed or capacity. One thing that long-time computer users will tell you is that you can never have too much space, so for most people getting the highest capacity at the lowest price is the biggest concern. If, however, your goal is not to archive vast amounts of information, but to get the highest speeds from your PC, you might look to faster (but lower capacity) drives, such as 10,000rpm drives. Even if you're not a speed freak, don't ignore this aspect of the hard disk. The hard disk is the part of your computer that you're most often waiting on, whether it be to open a new program, access virtual memory or load a new level in the game. A hard disk that's a little faster than the others can make a big difference to your computing experience. One thing you can do to optimise your system is use multiple drives, possibly in a RAID configuration (see below). A PC can have as many hard disks as its interfaces and case can afford. The easiest way to increase the storage capacity of your system is to add a new hard disk (you can usually keep you old hard disks as well, unless you run out of room). If you do plan to have more than one hard disk, there's a simple rule to follow - make the fastest one your system disk. This is the disk that has the operating system, stores the virtual memory and contains installed applications. It's the disk that is accessed most often, and because the head has to move around a lot, the access time is particularly crucial on this disk. It's also a good idea to keep this disk as free from clutter as possible and defragment it often (for reasons we'll explain below). If you do decide to get multiple drives, you can look to a RAID (Redundant Array of Inexpensive Disks) configuration. Many consumer SATA motherboards now support RAID 0 and 1, along with what are called JBOD (just a bunch of disks) configurations. RAID is entirely a function of the disk controller. A hard disk does not need to actively "support" RAID - any disk can be placed in a RAID. The basic principal of RAID is to arrange a group of drives into what appear to the operating system as a single drive. With the drives working together, a RAID array can improve a system's performance and data reliability. RAID 0, called striping, is where part of a file is stored on each disk. When the data is read, it is read in parallel from the disks in the RAID. Because each disk has to do less work, the overall speed of the file transfer is greater - RAID 0 can give you significant performance improvements. With RAID 0, the disks should to be similar is size - the total capacity of the array will be dependent on the smallest drive in the array. The big danger of RAID 0 is that if one drive dies, then all the data in the array is lost. For this reason, RAID 0 is rarely used for vital information. RAID 1, or mirroring, replicates all the data across all the drives in the array. This gives you reliability and speed (since it still reads data in parallel off multiple drives), but reduces your capacity. Say you had two 200GB drives, and set them up in a RAID 1. The total capacity of the array is only 200GB (not 400GB), because all the data on drive one is replicated on drive two. If one of the drives dies, then no data is lost (because all the data is still on the other). RAID 1 provides speed and reliability, at a huge cost in capacity. There are other RAID formats - 2, 3, 4 and 5 - with various levels of functionality, but these are rarely available without an expensive RAID expansion card, and are generally not seen in consumer PCs. JBODS are simply a way of agglomerating multiple hard drives into a singe logical drive. If you had a 10GB, 80GB and 200GB drive, you could make a JBOD of 290GB, appearing to the operating system as a single drive. They provide no performance or reliability benefits. File systems, fragmentation and slow downs A hard disk merely provides a way of storing data, it doesn't tell the PC how to organise it. That's the job of the file system. A file system is essentially a directory of the data stored on a hard disk. It's the PCs way of storing information on where files are physically located on the disk - for instance, that the file "fluffythecat.jpg" is located on track 31, sector 18 of the hard disk. Different file systems have different performance levels, and many quirks besides, such as the capacity of the hard disk they can support, support for encryption and how the geometry of the hard disk is divided up into addressable regions. One of the most important aspects of a file system is how it deals with fragmentation. Newer file systems, like NTFS, tend to deal with fragmentation much better. Fragmentation occurs when a file tries to fit into a gap on the hard disk that is too small for it. Say you delete a 10Kb file, which leaves a gap free on the hard disk. Then you try and write a 15Kb file. Only the first 10Kb can fit where the old file went. The rest has to go elsewhere on the disk, thus fragmenting the file. Fragmentation will require that the head jump from one part of the disk to another in order to complete the file reading. If the head has to move around the hard disk hither and thither, a lot of time is going to be wasted (this is why access times are so important). For this reason, defragging your disk periodically is important. Defragging will attempt to re-align files so that the entire file can be found in one place. In Windows XP, the defragger can be found under Start-Programs-Accessories-System Tools. One other thing that users often find is that hard disks get slower as they fill up. There is a very good reason for this: shorter tracks. Hard disks write first to the outside tracks of the platter, and then work their way in towards the centre. The outside tracks have a larger circumference than the inner tracks, and therefore each revolution of the hard disk covers more area on the outer tracks than it does on the inner (and thus passes more data to the read head). As the disk fills up, more data is being written to the slower inner tracks, and so you'll see an overall decrease in speed on that data. There's no real solution to this problem, except to keep your PC as free from clutter and excess data as possible. Defragging will move all the data to the outer tracks. |
Halfvalue.com Home | Halfvalue.co.uk | Compare Textbook Prices | Travel | Directory of All Stores
| |||
Your department store source to buy cheap used and new items online- - Store Directory - - - | |||||||||||||||
 | |||||||||||||||
| HOME | SITE MAP | BUY | BUY BOOKS | SELL | TRACK | TOP SEARCHES | ACCOUNT | PRIVACY POLICY | USER AGREEMENT | CONTACT US| AVAILABLE ITEMS| | BEST-SELLING BOOKS | MUSIC | PUBLISHERS | COMPARE TEXTBOOK PRICES | MORE BUYING OPTIONS |
| FIND A STORE | AUTO | BATH & BEAUTY | GIFTS | HOME IMPROVEMENT | JEWELRY | SPORTING GOODS | TOYS & HOBBIES | TRAVEL |
 |        |
