Overview:
There are many different types of storage devices for use with modern computers. I'll try to cover a few here. The Sharpie is used to show scale.
Most of the information stored on a computer is stored on the hard drive. Hard drives vary in physical size and storage capacity. In general, a hard drive is the largest storage device in your computer. It has many times more storage capacity than CD, DVD or electronic memory. A few years ago, a 20gig (gigabyte) hard drive was almost unheard of. Today, it's almost impossible to find a hard drive that has that little capacity. At the time that I'm putting this together (March, 2005), 400gig hard drives are readily available. The common hard drives found in todays computers are called 3 1/2" (three and one-half inch) hard drives. This is the most common size. They fit into the 3 1/2" drive bays in your computer. Laptop computer hard drives are called 2 1/2" hard drives. They are much smaller than the desktop computer drives and typically consume less energy but they are generally slower. A few years ago, at least one company made a 5.25" hard drive but no one (as far as I know) makes 5.25" hard drives for personal computers.
Note:
I want to clarify that a 3 1/2" drive isn't 3.5" wide. It's about 4" wide. The media platters in the drive are 3.5". The 5.25" drive is actually close to 6" wide. The name likely comes from the old 5.25" floppy drives that were the same width.
Hard Drives:
In the image below, you can see a standard hard drive. As you can see, I've removed the top cover (never do this to a drive in good working order - one tiny particle of dust can destroy the drive). The 'platters' you see are where the information is stored. The arm that you can see on top of the platter is where the read/write heads are mounted. There is one head for each side of each platter. There are 2 platters in this drive. As you can see by the reflection of the flourescent lighting on the ceiling, the platters have a mirror-like finish. When the disc drive searches for information, the arm will move across the platter (never touching it) and read/write the data. In some drives, the platters spin as fast as 15,000RPMs (revolutions per minute). In this old drive (made in 1996), the platter probably spun at 5400RPMs. Most modern 3.5" drives spin at 7200RPMs.
Note: MOST hard drives have 2 heads per platter (one on each side). The previous drive only has 3 heads. The arm that you see in the picture has no read/write head. In a later chapter, I will show you what the actual heads look like.
CD-ROM Drives
CD-ROM and DVD-ROM drives (both fall into the category of optical drives) are very popular. Virtually every computer in use has a CD-ROM drive and most have CD drives that can burn (record onto) CD-R (Recordable) and CD-RW (CD Re-Writable) media. Virtually all of the new computers have 'combo' drives. A combo drive can read and write on CDs but they can also read DVDs. This allows the user to watch DVDs on their computer. The cost of a combo drive is barely more than a CD-ROM drive so it makes good sense to include them.
The following image is a CD-ROM drive with the cover removed. There's really not much to see but I thought it would be interesting for those who have never been adventurous enough to take their drive apart.
In the next image, you can see a close-up of the laser 'pickup' mechanism. The coils of wire on the sides, keep the lens (center of pickup) in focus and on track. Since the magnetic coils have limited range, they only fine tune the tracking of the data on the disc. For moving long distances, the pickup is motivated along 2 metallic rods by a worm gear.
Floppy Drives:
As I mentioned before, there were some large (5.25") 'floppy' drives. These drives used discs that were actually floppy. The newer floppy drives use the same basic recordable medium but it's in a hard shell. The newer floppies are smaller also. They're approximately 3.5" across. As of late, these drives are becoming rare. Just about the only time I use them is when I have to load some sort of driver when loading an operating system onto a computer. Frankly, I'm happy to see them go. From my experience, they are VERY unreliable. I rarely get more than a few uses from a disc and the data on them gets lost regularly. The image below shows a 3.5" floppy without its cover. This is one of the only drives where the disc read/write touches the media. On the back of the drive, there's a motor that drives the head across the disc surface. As you can see, there is an orange disc in this unit.
Laptop Drives:
As I mentioned before, the drives for 'laptop' (notebook) computers are smaller. They also spin more slowly (although there are some that spin at 7200RPMs). Spinning more slowly means that it takes less energy to spin the disc. Remember that loptops are often run off of batteries and reducing energy consumption is important. Even new laptops use the slower (4200RPM) drives. For many people, they are simply too slow (they make even a computer with a fast processor sluggish). For those people, faster drives are available. The extra speed/responsiveness is well worth the somewhat reduced running time when on battery power. Below is an image of a laptop drive.
Drive Enclosures:
Many times, it's necessary to transfer large files (video, audio) from one computer to another. To do this, many people use a portable hard drive. Most portable hard drives are simply 3.5" hard drives in a protective case. Typically, the case has a power supply of some sort. For 3.5" drives, the power supply is usually plugged into a wall outlet. For laptop drives in portable enclosures, they draw less current and therefore can get power from a USB port. Since a USB port is only capable of safely supplying 1/2 amp of current, some enclosures have a splitter that pulls power from 2 USB ports. The image below shows the dual USB plugs.
The following image shows the laptop drive with the enclosure. Notice that the power supply/interface board of the enclosure is plugged into the back of the hard drive. Enclosures for 3.5" drives are essentially the same but large enough to accommodate the larger drive and requisite power supply.
USB Pen Drives:
For those who need to transfer small to medium sized files, a USB flash memory drive (also known as 'pen' drives or 'jump' drives) may be exactly what you want. They are available in sizes up to about 1 gigabyte. The following image shows a Sandisk brand pen drive. This one is 256 megabytes. The higher capacity drives are not necessarily physically larger they can simply hold more data. Pen drives from other manufacturers will look considerably different but serve the same purpose. They all plug into the USB ports and are recognized by the computer as a new hard drive. For Windows XP, 'drivers' are not needed. For older operating systems like Windows 98, you have to load drivers for the computer to recognize the drive.
Note:
Drivers are files that contain the information that the computer needs to use a device. For newer operating systems, like XP, the drivers are loaded automatically (most of the time). For older operating systems, you have to manually load the files. For most devices, the drivers are provided on a CD-ROM. If you have a device that needs driver but you lost the disc, the drivers can usually be downloaded from the manufacturer's web site.
Below, you can see three multi-conductor cables. The two on the left are IDE cables and they're used to connect the hard drive to the motherboard. The one on the right is a floppy drive cable. It's used to connect the floppy drive to the motherboard. If you look closely, you can see that the two cables on the left both have 40 pins but one has more individual conductors (80 conductors to be exact). The cable on the left is the newer style cable and is required for today's faster data transfer rates. The extra conductors are used for shielding between data lines. The 80 conductor cable allows automatic selection between 'master' and 'slave' drives when the drives have their jumpers set to CS (Cable Select). The 40 conductor cable requires that you set the jumpers on the drives manually. The floppy drive cable has 34 pins/conductors.
In the picture below, you can see the 40 pin IDE connector. Notice that it has two ways to assure the correct polarity. The first is the missing pin. It works to assure that cables like the one in the center above are properly connected. The other way it assures proper connection of a cable is by having a protrusion on the outside of the connectors (as the cable on the left has). This connector is standard on most optical and IDE drives.
In the image above, the connector all of the way to the right is the 4-pin Molex power connector. It's standard on IDE drives.
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