From CTLpedia
by Ken Costello
PROBLEM & SOLUTION:
Sometimes we feel stuck in ancient times while trying to understand all the new technology. This makes us feel left out. The answer is to become multimedia literate. You don't need to know how to use multimedia but knowing the basic concepts and terminology will make you feel better connected to this technology and ready to learn more.
This tutorial follows a logical and chronological progression for multimedia literacy; however, you can jump to a specific topic. The topics below are the subjects for each of the panels that follows.
LOVE OF ACRONYMS:
Our society loves to use acronyms. For example, we know the acronyms of our government agencies more than the actual names: FBI, CIA, [[Image:DOE, etc. All discplines use acronyms, but is [[Image:seems that computer science uses the most. Also, email shorthand has really boosted the use of acronyms.
Acronyms make conversation and writing more efficient. Unfortunately, it confuses those who do not know what the acronym stands for. Plus one acronym can stand for many things. For example, on this box of Alpha-Bits is the acronym "RCM." A Google search finds Royal College of Midwifes, Risk Center Management, Reciprocating Chemical Muscle, and the list goes on. This trend gets worse...
CALCULATOR TEXT:
If you hold a calculator upside down, the numbers will resemble letters. This allows students to write a text message to their friends sitting next to them in class with just a calculator.
So our letter acronyms can get more confusing because numbers can be substituted for letters if they resemble letters either upside down or upright.
IF GEEKS RULED:
Here's what Alpha-Bits cereal would look like if geeks designed it. Notice letters are replaced by numbers that are similar in shape.
The acronym "ASCII" is an alphabet for computers. It stands for American Standard Code for Information Interchange.
Computers, like all machines, "understand" on and off very well, but a single on and off switch could only represent two things, but if you used a series of eight on and off signals, much more can be represented. A series of eight switches have 256 different combinations so many things can be coded in those combinations. Our alphabet only has 27 letters so both upper and lower case letters can be coded.
ASCII:
The ASCII system assigns different combinations of on and off switches to different letters and different commands. The top set of on and off switches to represent the letter "A".
The second row of switches represent the letter "B" in ASCII. The bottom row is "C".
In the Alpha-bits name, "bits" means small pieces of cereal. In computer jargon a "bit" is one of these switches. Eight bits are used in ASCII to code the alphabet, punctuation, other characters, and commands (to devices like printers).
BIT, BITE & BYTE:
A set of eight bits (switches) is a called a "byte". You've heard the expression, "Eat a little bit" and "Take a big bite." "Byte" is just a play on the word "bite" as something bigger than a "bit".
By the way, a "nybble" is half a byte or 4 bits. Nybble, of course, is a play on the word, nibble.
ALPHABET SOUP:
Let's dive into the alphabet soup of acronyms that muddy up the understanding of multimedia.
There are three categories:
1. Audio/Video
2. Various Storage Formats
3. Computers
Let's begin with the world of audio and video. Let's also look at an historical development of these areas.
TAPE RECORDINGS:
Tape recorders can be made to record audio, video, or just data. This one recorded radar data. It took a mile of tape to come up to speed and a mile of tape to stop. The tape moved at 60 mph and recorded only 5 minutes of data. In today's money it would cost about 6 million dollars.
Recorders like this one were modified to record music as well. Imagine spending 6 million dollars to record one song. That's why vinyl records were used instead. Recorders like these, however, had metal tape that could be erased and reused. You just didn't want to be standing by it when the metal tape broke; you'd be cut to ribbons.
Video Tape Recorder (VTR):
This is a video tape recorder with it's accompanying video camera. It first came out in 1962 for home use. The videotape was on reels like the tape in audio tape recorders of the time. It wasn't very portable as you can see.
The acronym was VTR, short for video tape recorder.
I remember owning one like this. The recording was only in black and white. The tape, I believe, was the same size as we see in VHS video cassettes, however, it was on a reel, just like an reel-to-reel audio recorder. The problem with tape on a reel is that it is exposed to dust and fingerprints.
Video Cassette Recorder (VCR):
Videotape on a reel is exposed to dust, so they designed a cassette holder to protect it. This video recorder is therefore called a VCR (video cassette recorder). The recording speeds were SP (standard play-2 hrs), EP (extended play-4 hrs), and SLP (super long play-6 hrs). Note: Use SP for recording; the quality is much better.
Sony's Betamax was the other kind of home video cassette recorder. It was capable of recording more detail but the recording time on the tape was less. Most buyers chose the VCRs that recorded longer.
8mm Tapes & Films:
Later Sony (and others) made smaller video cameras that used 8mm (millimeter) wide tapes. The Hi8 tapes were the same size but capable of higher detail. Note that 8mm
film has been around for over 70 years, so to prevent confusion, say
8mm videotape when you mean
videotape and say
8mm film when you mean
8mm film.
LASER DISCS:
Laser discs came out in 1978. The first movie was Jaws. The disk is 12 inches in diameter. Laser discs were popular with videophiles because of the high quality video. It also could do slow motion and jump to scenes that videotapes could not.
When DVDs were released, the production of laser discs stopped. Laser discs never had copyguard protection on them, so the video signal was always good. That can't be said of DVDs.
COMPACT DISC (CD):
In 1982, the compact disc (CD) was created for audio. You now know why it is called compact disc (CD) because it is about 5 inches instead of 12 inches in diameter. Note: The spelling of disk versus disc is somewhat interchangeable; however, it seems that laser and CDs use
disc and floppy and hard drives use
disk.
Music CDs are digital recordings meaning that every CD of that album are identical and if you made a copy of it, the copy would be identical to the original. This wasn't true of music albums on records or audio cassettes.
CD ADVANTAGE:
Compact discs are used for audio, data, and video. Audio CDs provided an alternative to the audio cassette. Audio tape would deteriorate by stretching and being scratched by dust. Audio CDs are only touched by a laser beam, so they don't wear out.
Also, as mentioned above, a copy of a CD is identical to the original.
FLOPPY DISKS:
Floppy disks are made from the same material that videotape and audio tapes are made from. They are made from iron oxide (rust) stuck to plastic. Like tape, the disks are also flexible (floppy), hence their name. The 3 1/2 inch disks seem hard, but that's just the case. Inside is the floppy disk (see bent floppy disk).
Floppy disks were notorious for becoming unusable because the iron oxide coating would wear off making that part of the disk unreadable. Many a computer users lost their data because they kept their data only on floppy disks.
Tape & Disk Surface Wear:
To be read, videotapes, audio tapes, and floppy disks have to slide across a metal surface that has a gap that houses a small coil of wire. This coil (called a pick up head or read/write head) senses the magnetism in the iron oxide particles on the surface of the tape.
The strength of the magnetism gets translated to sound, video, or bytes of information. The friction here causes the tapes to wear out. This is one reason CDs became much more popular.
By the way, credit cards also have a strip of magnetic tape on them. You have to swipe the cards quickly because that causes the magnetic regions on the card to induce a stronger signal in the pick up coil (head).
CD-ROM STORAGE:
Not only would floppies wear out, they didn't store much. It takes about 500 floppy disks to store the same as one CD-ROM. It would also take about 25 hours to read the data from the 500 floppies versus about 5 minutes for one CD-ROM. Software companies were quickly switching to CDs for installation into buyers' computers.
ROM vs. RAM:
CD-ROM leads us to two acronyms, ROM vs RAM. To understand these terms we need to look at the early ways data was stored. Data was stored on reels of tape. This allowed huge amount of storage. The only problem was that to get to some data in the middle of the tape, the tape would have to be unwound onto another reel.
It's the same as a videotape. To find a scene or piece of data, you have to scan through the tape to find it. You could not just randomly jump to a scene or data on the tape, you have to get to it sequentially. In other words, tape storage is not ROM or RAM as you will see below.
MAGNETIC REGIONS ON TAPE:
Recall that the switch pattern shown below is the letter "C". A certain length of tape is needed to store characters. If magnetized with this spacing shown to the right, the computer sees it as a "C." Here the spacing is exaggerated to coincide with the switches. In practice, the magnetized bands were very narrow.
TAPE ADVANTAGE:
The tape holds a lot because it's about a half mile long. If cut into pieces, it could cover a good size living room (200 sq. ft).
That gives a lot of surface area for storing magnetic bits (a region either magnetized or not). However, the shortcoming was having to access information by scanning through the tape as it wound to another reel.
QUICK ACCESS TO DATA:
Instead of magnetizing the iron oxide on a tape surface, magnetizing spots on a disk had one huge advantage. One could get to any information on the disk by simple moving the pick up head (a small coil of wire) to the place where that information was stored. In other words, you could randomly chose what data to read. This is one form of Random Access Memory (RAM).
DISK LAYOUT:
Information on a disk is organized by tracks (rings) and sectors (pie shape areas). By knowing which track and sector, the pick up head can go straight to that data. That happens in a few thousands of a second, where as finding data on a tape may have taken minutes.
CHALLENGE: The challenge with a magnetic disk is that the magnetics spots have to be very small because instead of having 200 sq. ft of area (like a tape), you have about 20 sq. inches. So the magnetic spots have to be over 1000 times smaller.
WHY A HARD DISK?
When these magnetic spots sweep by a coil (shown below), it causes electrons to move in the coil. This is how the the bits (data) are read. With magnetic spots so small, their magnetism is weak. To compensate the disk is spun very fast (about 7000 revolutions per minute) which increases the spots ability to generate current in the coil). At those speeds the flexible plastic that is used on magnetic tape or floppy disks would not hold up. These disks had to have a very stiff surface. That's why they are called hard disks.
CLOSE BUT NOT TOUCHING: Also, the surface of the disk could not touch the pick up coil (head) because at those speeds the friction would be too great. So the head is designed to float above the disk. As the disk spins, it spins air with it. This air lifts the head about 5 millionths of an inch above the surface of the disk. Close enough to sense the magnetic spots but far enough to keep from scraping the disk.
HARD DRIVE CRASH:
You've probably heard someone say "my hard drive crashed". A true crash is when the pick up head falls into the fast spinning hard drive disk and scrapes up the surface. There is no recovery from this kind of crash. Sometimes a computer "crashes" because data in memory gets corrupted, but that isn't a true physical crash and rebooting gets it going again.
Hard drives don't crash to often, but often enough to be sure to have backups. When your hard drive crashes, you can lose a ton of data.
RAM Memory:
RAM stands for Random Access Memory because it lets you access memory (data) without reading through unwanted data, such as tape storage requires. In other words you can randomly retrieve data in any order you want, which is opposite of tape storage.
Random Access Memory is memory that is stored on a disk or computer chip that allows random reading of any data on that device. The popular thumb drives (flash drives) are examples of Random Access Memory.
RAM vs. ROM Storage:
All disk storage is Random Access Memory (RAM) because data can be retrieved directly by jumping to a particular track and sector.
RAM also implies that not only can you retrieve data in any order, you can record data to any free track and sector. If data can be read in any order (RAM) but can't be written to device, it is called ROM (Read Only Memory).
RAM is memory that you can write and retreive data. ROM is memory that can only be read. The computer chips that bootup your computer or run electronic devices like cellphones and calculators are ROM chips.
CORE MEMORY RAM:
Discs allow random access memory, but the disc has to spin and the read/write head takes time to move to that track and sector on the disc. A computer needs faster reading and writing of data to be efficient. In the 50s and 60s, small magnetic beads (cores) were strung together by wires that act as electronic memory. This had to be done by hand while looking through a microscope.
Workers in Asia were hired to do this tedious job. Initially it cost one dollar for each bead. These acted the same as a switch. They could be magnetized (on) or demagnetized (off). It took eight of these beads (cores) to make a byte, which stores one character (letter).
The image is a plane of core memory (about 2K of memory).
CORE MEMORY STORAGE:
This refrigerator size box houses planes of core memory (each square you see). I estimate it holds about 16 million beads (cores), which is 16 million bits or 2 million bytes (2 megabytes). The cost could have been 16 million dollars.
Nowadays, that amount of memory is about ten cents. Even though expensive, the computer could manipulate memory fast enough for calculations and sorting. Earlier computers used vacuum tubes for memory. So this kind of memory was immensely better and smaller.
This was the first kind of computer that I saw. It was at Honeywell in northwest Phoenix in 1968. Later, when I saw newer computers, I wondered what happened to those little beads.
CD-ROM:
Here is this picture again. A CD used for software installation or data storage can hold the same as 500 floppy disks, but data can only be read from it and not written to it. That's why it is called a CD-ROM. It's Read Only Memory.
ROM also refers to computer chips that are used for reading information and not for storing information.
CD-R:
This stands for Compact Disc-Recordable. When first introduced in 1988 it was called CD-WO, meaning Compact Disk-Write Once, which better explains its purpose. You can record on it once, but you cannot erase it and record again.
A CD-R can be used to make a standard audio CD (74 minutes for the CD shown) or used to store computer data (650 Megabytes). Other types hold 80 minutes of audio or 700 Megabytes of data.
The prices of CD-R discs have dropped drastically, allowing backup of information rather cheap. Before CD-R discs people used tape backup devices or Syquest brand of removeable hard disks. A Syquest disk stored up to 250 megabytes and cost about 10 dollars. Fortunately, it could be reused.
DATA VISIBLE ON DISC:
Above are two CD-R disks. They look different because companies use different dyes. The dyes become more opaque when a strong laser beam strikes the dye. When the laser is off, the surface stays reflective, when it turns on, the dye becomes opaque. The laser is turned on and off in a pattern just like we did for the switches earlier. If you look closely, you can tell if a CD-R has data on it. The recorded area has a different amount of reflection. Also note when cleaning the CD wipe from inside to outside. Do not wipe in circular motions.
CD Markers:
It is recommended to only use CD Markers if you write directly onto the CD. Otherwise use a CD label or a small mailing label. Other pens have inks that can be absorbed and change the reflectivity of the CD.
I have to confess that I've used a multitude of pens and most were not CD markers. I don't think I've ever had a problem.
CD-RW:
Unlike CD-R, CD-RW discs can be written to, erased, and rewritten to. It stands for Compact Disc-ReWritable. CD-RW discs are not as compatible with CD players as CD-R. Because CD-R discs have gotten so cheap, CD-RW are not used as much. So in general it is better to buy CD-R discs for transferring large files or for archiving computer data or music.
DVD:
Officially this acronym has no meaning. It originally stood for Digital Video Disc. Later some in the group that regulate DVDs wanted to call it Digital Versatile Disc because it can store other data besides video. They never agreed, so the acronym has no official meaning.
The disks have two layers of dyes that record data and holds 9.4 gigabytes (9,400 megabytes) compared to 700 megabytes for CDs. The recordable DVDs that we use to store data or video are called DVD-R,DVD-RW, DVD+R, DVD+RW. They store 4.7 gigabytes of data.
Twister was the first movie to be released on DVD in 1996. DVDs quickly shutdown the production of the Laser Disc movies and soon will end the release of movies on VHS.
CRT:
To draw an image on a screen, the first and longest method has been with a CRT, which stands for Cathode Ray Tube. It didn't begin as a way to make an image but a way to make Xrays. If you take a glass tube and evacuate most of the air and apply high voltage across two plates that are inside the tube, electrons will leave the negative plate (the cathode) and travel to the positive plate. As the electrons fly from the negative plate to the positive plate, it makes the air glow like a beam of light (a ray). When the electrons slam into the positive plate, it gives up its energy as xrays. These continue on and will pass through objects. A photographic film will be exposed by the shadow of the xrays revealing the inside of objects.
CRT as a Picture Tube:
The original CRT was modified (see above image). As before electrons would leave the negative plate (cathode) and be attracted to the positive plate, but the positive plate had a hole in it allowing the high speed electrons to continue on. Other plates with plus or minus charge would deflect the beam up or down and left or right. Electromagnets are used to narrow the beam (make the beam sharper). The electrons are directed to hit spots of fluorescent material on the front surface of the tube causing the them to emit light. Three different fluorescent phosphors were used. One emitted Red light, another Green light, and the third Blue light. The colors are referred to as RGB.
RGB:
The letters RGB are used many ways. A computer monitor is often referred to as a RGB monitor because it receieves separate signals for red, green, and blue. A standard television uses red, green, and blue phosphors but the signal to make control those colors does not come as separate signals for red, green, and blue (RGB).
