Computer/Technical Jargon
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Internet Address Explinations
http://www.mysite.com
Take the above example. Each section has a different color. The section in red tells the browser to
use the HyperText Transfer Protocal, which is the World Wide Web.
The www. part specifies a particular web server, computer, or folder.
www. is the server you go to for the main site (note that www. is sometimes optional). For
instance, http://www.wikipedia.org/ is the master site for Wikipedia,
http://en.wikipedia.org/ is the English site for Wikipedia, and
http://ru.wikipedia.org/ is the Russian site for Wikipedia.
The purple part is the domain name. Domain names must be
leased from the owners of the TLD, mentioned next. Finally, the extension lets the Domain Name
Server, a computer with a collection of domain names, know where to look. These extensions are called Top Level Domains (TLD). Each
country has a specific a TLD in addition to the generic ones, like .com. Each TLD means something. For instance, .com means
commercial and is owned by VeriSign, .edu means education and is only available to universities, .gov means government and is only
available to the US Government, .org means organization is only available to non-for-profit organizations, .us means United States,
.uk means United Kingdom, and so on. In addition, owners of these extensions may add prefixes to these TLD's. For instance, .co.uk is
the United Kingdom equivalant of our .com. The extension is a good way to tell where the site is located, but remember, sometimes the
owner of these extensions allow people outside of their country lease these TLD's. In any event, all of this is just for convience to
you and I, as all web sites have an IP address, which are harder to remember. The IP address is 4 or 16
bytes with each byte seperated by a period and is unique. Remember, a byte is 8 bits or an 8 digit binary number. An 8 digit binary
number can have decimal values between 0 and 255. For convience, IP addresses are not written in binary but in decimal. Therefore, IP
address have a range between 0.0.0.0 and 255.255.255.255 which allows 4,294,967,296 unique combinations. No other computer may share a
public IP address. However, certain IP addresses are reserved for private networks, such as for homes or businesses. These private IP
address must be unique within a private network but not the internet as a whole. For instance, if you have high-speed internet and a
router, the router will give you an IP address. Another person can have the exact same router and it would give them the exact same IP
address. The router has the public IP address and routes the data as needed. The private IP addresses are 10.0.0.0 to 10.255.255.255,
172.16.0.0 to 172.31.255.255, 127.0.0.0 to 127.255.255.255, and 192.168.0.0 to 192.168.255.255. These IP addresses may only be used
for private networks. Also, the IP address 127.0.0.0 is a loopback to your own computer. It is used for testing.
Popular Digital Media Specifications
| Media | Size | Capacity |
| Blu-Ray | 120 mm diameter | 25, 50, 100 GB |
| CD | 120 mm diameter | 180, 650, 700 MB |
| Floppy Disk | 5.25, 3.5 in square | 360, 720 kb, 1.44, 2.88 MB |
| DVD | 120 mm diameter | 4.7, 8.5, 9.4, 13.7, 17.1 GB |
| Hard Drive | 3.5, 2.5, 1 in across | 20 to 750+ GB |
| HD DVD | 120 mm diameter | 15, 30, 51 GB |
| USB drive (Jump drive or Flash drive) | Variable | 32 MB + |
Popular Digital Audio/Video Formats
| Format | File Extention | Lossy | Notes |
| AAC | .m4a, .m4p | Yes | Used for iPods, developed in part by Dolby Labs. Rivals OGG Vorbis for the best sound quality. |
| Apple Lossless (also ALAC or ALE) | .m4a | No | Used for iPods. |
| ATRAC | .m4a, .m4p | Yes | Used for Sony MiniDiscs and some Sony audio devices. Considered inferior to MP3. Sony retired this format. |
| DivX (also MPEG-4) | .divx or .avi | Yes | A popular alternative to MPEG-2 as it uses a lot less space for the same quality. Some DVD's player support this, but right not no DVD players support the HD modes. |
| Dolby Digital (also AC-3) | .ac3 | Yes | The de-facto DVD audio standard. |
| Dolby True HD | n/a | Yes | Used on some HD-DVD and Blu-Ray movies for superior sound quality. |
| DTS | N/A | Yes | Slightly better than Dolby Digital for DVD's. |
| H.264 (also MPEG-4) | .m4a, .m4p | Yes | Video used on some Blu-Ray discs. Not used on production HD DVD's, but all players support it. Superior to MPEG-2. |
| HE-AAC (also aac+) | .aac | Yes | Used by XM radio, provdes the best lossy sound quality. |
| MP3 | .mp3 | Yes | Almost universally compatible with all audio devices. |
| MPEG-2 | .mpeg or .mpg | Yes | The video format used for DVD's and digital cable/satellite TV, all HDTV broadcasts, and many Blu-Ray discs. Inferior to VC-1. |
| OGG Vorbis | .ogg | Yes | Very little support because its backers aren't rich and it has no way to secure purchased audio. Rivals AAC for the best sound quality. |
| RealVideo | .rma | Yes | Probably the best streaming video format. |
| WMA | .wma | Yes and no | Created by Microsoft, almost every audio device except iPod supports it. Superior to MP3 but inferior to AAC or OGG Vorbis. |
| VC-1 (also WMV-9) | n/a | No | The standard used on all HD DVD's and some Blu-Ray discs. Provides the best possible picture but uses half the space of MPEG-2. |
| WMV/WMV HD | .wmv or .avi | Yes and no | Created by Microsoft. Can support HD quality video. |
Greek Prefixes Used for Computers
| Prefix | Abbr. | Normal Value | Data Value | Usage |
| nano | n | 10-9 or 0.000000001 | N/A | Transitor size are now denoted in nanometers. |
| micro | μ | 10-6 or 0.000001 | N/A | Transitor sizes used to be denoted in micrometers (or microns). |
| milli | m | 10-3 or 0.0001 | N/A | CD/DVD's are 120 millimeters |
| kilo | k | 103 or 1,000 | 210 or 1,024 | Kilobyte, kilohertz |
| mega | M | 106 or 1,000,000 | 220 or 1,048,576 or 1024k | Megabytes, megahertz |
| giga | G | 109 or 1,000,000,000 | 230 or 1,073,741,824 or 1,048,576k or 1024M | Gigabytes, gigahertz |
| tera | T | 1012 or 1,000,000,000,000 | 240 or 1,099,511,627,776 or 1024G | Terabytes |
| exa | E | 1018 | 260 | Exabytes |
The Data Value is the value of that Greek prefix when used computer data, since that has two states, on and off, and not 10 like we use in counting. Just to keep you confused, not all things in the computer world use the data value, but use the normal value. Hard drives are measured by the normal value instead of the data value to make you think you are getting more space than you are.
How a Hard Drive Works
A hard drive has 4 different key components: the controller, the platters, the motor, and read/write head. Let us start with defining the different pieces of the hard drive. Then we'll move on to how they interact together. This article does not go into the very technical details of how a hard drive works. For instance, how data is stored on the surface is not covered.
The platter is what your data is stored on. There may be several. Older hard drives always listed how many platters were inside because you had to know in order to properly setup the drive. That information is no longer necessary, so you may not know how many platers there are without opening the hard drive. The plater may be made up of aluminum or glass coated with a magnentic substance.
The motor spins platters. ATA hard drives spin at 5400 or 7200 and sometime 10,000 RPMs and SCSI hard drives spin at 10,000 RPMs and beyond. Motor speed affects how fast raw data can be transferred.
The read/write heads is what magnatizes and reads the magnentic polarity of data. It sits less than the width of a hair off the platter. In fact, it requires the air from the spinning platters to keep from making contact with the platter surface. If the head did make contact, that would be a head crash. Head crashes may or may not damage your data or platter, it all depends on the severity of it. When powered down, the head move to a safe zone, called a landing zone. This prevents head crashes. Because the heads sit so close to the platter, if anything at all gets into the hard drive, it can destroy it. Thus, hard drives are made in dust-free clean rooms.
Finally, the controller. In a computer, all your data is transferred to and from your computer through cable that is 7 pins, 40 pins, 50 pins, 68 pins or 80 pins. For most people, the cable will be 40 pins on older computers and 7 pins on the newer. In ATA, the controller is located on the hard drive and is called IDE. That is why ATA hard drives are often (wrongly) called IDE hard drives. The controller queues the data and manages transmission.
Hard drives, like monitors, are always measured in inches. A 2.5 inch hard drive is used for laptops, 1 inch hard drive for devices like iPods and portable storage, and 3.5 inch hard drive for everything else.
When a request is sent to the hard drive, it is either processed as a first-come, first-serve basis or in the most efficient possible way. The latter method is a new technique called Native Command Queueing or NCQ. The first thing that has to be done is to find the data wanted. First, the hard drive reads the File System to find where the file starts. Next, the read/write heads move into position. A sector is read. In Windows, a sector is 512 bytes. Each sector will contain data to locate where the next sector of this file is. Ideally, sectors for each file must be back-to-back and not in fragments all over the hard drive. When they are not back-to-back, read times are significantly slower. Defragmenting the hard drive will put all sectors back-to-back.
When writing data, the operating system has to find a space marked unused by the file system. Note, data is may still there, but has been deleted. When a file is deleted, the space it occupied is marked free. The file is not trully deleted until overwritten by more data. Once free space has been found, data is written there.
A similar process is used for all other forms of media. There are variations for optical media like CD's and DVD's, but the process is generally the same.
What is the difference between a disk and disc?
A disc is round. Think of the discus that is thrown during the Olympics. CD's, DVD's and such are usually round, thus they are discs.
A disk is a general term for a whole storage device.
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