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More on Hard Drives
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Although the the next three images will not really further your knowledge of computers, I thought a few people might be interested in seeing them. You'll have to excuse the quality of the second and third images. The object is almost microscopic. The image immediately below is the magnetic actuator out of the hard drive I showed you on an earlier page of the tutorial. At the far left are the heads. To the far right, you can see the 'voice coil' of the magnetic actuator circuit. There is a strong permanent magnet in the base of the hard drive. When voltage is applied to the voice coil, the electromagnetic field interacts with the field of the permanent magnet and the actuator moves.
![]() And this is a little closer...
![]() The image below is the side of the head assembly that is closest to the platter. On this old drive, when the platters spin down, the head assembly rests on the platter. On newer drives, the heads are moved off of the platter before they spin down. On newer drives, the heads never touch the platters under normal operating conditions.
![]() The following image shows the end of the head assembly. The head is the little shiny spot in the middle of the epoxy (where the wires terminate). Although you can't tell from the picture, the wires (two twisted together) are about 1/2 the size if a human hair. On a hard drive this old, it's possible that the head uses a coil of wire as a magnetic pickup. On newer heads, they use a different (magnetoresistive) technology that allows tighter spacing of the tracks on the disc platter which allows higher capacity. The new drives can get 100GB or more on a single platter. This drive had only 1.6GB per platter.
![]() The following image shows a different hard drive that allows a better view of the platters.
![]() This is a wide shot of the platters, actuator arms and heads.
![]() In this close-up of the drive, you can see how the heads sit on the platters. If this were a working drive and the platters were stopped, the heads would be near the center of the platters (near the spindle) in what's known as the 'landing zone'. The landing zone is an area where there is no data. On newer drives, the heads would be moved off of the platters before the platters stopped. Remember that on new drives, the heads never actually touch the platters. They 'fly' just above them on a cushion of air.
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Capacity: Average Seek Time: Average Latency: Buffer Size: Rotational Speed: Interface: Form Factor: NCQ:
Until now, we haven't gone into much detail about the way a hard drive is structured. As you know, the hard drive has a series of stacked platters. The platters are essentially set up the same way in all hard drives. There are slight variations but the following is a good general description of the common hard drives used in personal computers. Tracks, Sectors and Clusters:
Cylinders:
Other Information on the Hard Drive:
Earlier in the tutorial, i showed you a picture of an older hard drive with the cover removed. It's heads and actuator arm are shown at the top of this page. The hard drive you see below is a newer hard drive. It has some things in common with older drives and there are some new features. The drive below is Western Digital Raptor SATA (Serial ATA) drive. It's designed to be faster than the average drive but there are tradeoffs in the design. It approaches the speed of some SCSI drives but costs significantly less than a SCSI drive. These high-performance will typically run hotter than a standard drive. The average drive spins its platters at 7200RPMs. The drive below operates at 10,000RPMs. Keeping the platters spinning that fast simply takes more energy and causes the drive to run hotter. The upside to the high rotational rate is that the information comes around to the heads more often than with the 7200RPM drives (lower average latency). Note:
![]() If you look at the connectors on the drive above, you can see that the connectors are significantly different than the connectors on the rear of the CD-ROM drive that was shown on the 'storage' devices page. The drive above uses a different data cable and has the option to use the new style power cable or the standard 4-pin Molex. The image below is the bottom of the SATA drive and gives you a somewhat better view of the connectors.
![]() The image below is the SATA data cable connector. As you can see, it's quite a bit smaller than the 40 pin IDE cable. This makes it easier to route the cables, reduces clutter and allows for better air flow through the case. They also have a longer maximum length than IDE cables (which are limited to 18 inches).
![]() These are the SATA power connectors. There's nothing special about them really. If you buy a SATA drive and your power supply doesn't have SATA power connectors, the Molex to SATA adapters are readily available.
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Do not try to change, add or remove the partition on any drive unless you know precisely what you're doing. The slightest mistake may leave you with an inoperable computer and all loss of data on your hard drive. The following image shows the disk partition manager for Windows. It shows all of the partitions on all of the hard drives. As I mentioned earlier, notice that the main drive (the 40GB Samsung drive that you saw in the 'inside the computer's case' page) has 2 partitions. The small laptop drive in the external USB drive case has only one partition.
![]() On most computers, the entire hard drive space is one partition (sort of like a large building with no internal walls to divide the living space into individual dwellings/apartments). When you set up multiple partitions, you are essentially putting up walls in that building. There have been times that the Windows OS quit working properly for one reason or another (virus, disc error...). Sometimes, the problem is severe enough that you have to reformat (erase and start anew) the entire partition where the OS resides. If you have to wipe the entire partition and you have all of your photos and music on the same partition as the OS, you lose everything. Many times, if your files are on a separate partition, they are safe. I generally setup a 15GB partition for the operating system and programs and leave the rest for my files (in a second partition). Also, if you like to keep your hard drive defragmented, it takes less time to defrag individual partitions than it takes to do the entire drive. If you import/export a lot of large files (like video files), you will badly fragment your hard drive. Doing the video editing on a partition other than the one where your operating system is, will help prevent the OS partition from getting fragmented. Defragmenting: Formatting: NTFS/FAT32: On IDE drives (the ones that use the 40-pin connectors), there are jumpers on the back of the drive. These jumpers tell the motherboard which drive is going to be the master drive (the master drive holds the operating system) and which is going to be the slave drive. As you can see in the image below, there is a red jumper connected across one pair of pins. Beside the red jumper, there are two more pairs of pins.
![]() If you look at the next image, you can see some markings on the bottom of the drive. 'MA' denotes 'master'. SL is slave and CS is cable select. This drive is set to CS (there's a black jumper in this image). If you're using a 40-pin, 40 conductor cable, you must set the jumpers properly for the master and slave drives. In most simple systems, the hard drive is the master and the CD-ROM drive is the slave (if both drives are on the same cable). If you have a 40-pin, 80 conductor cable, you can set both drives to CS and the drive plugged into the end connector on the cable is the master. The drive plugged into the middle connector on the 80 conductor cable is the slave.
![]() In this image, you can see an 80 conductor cable. On the left is the motherboard connector. To the far right (black) is the master drive connector. In the center (but closer to the master connector than the MB connector) is the slave connector. Sometimes, you will have only one drive on a cable. If that's the case, use the connector on the end of the cable (some systems are sensitive to reflections along the cable and will cause errors). If you have a 40 conductor cable, set the single drive as a master.
![]() Jumpers on SATA Drives:
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