ANALOG vs. DIGITAL is a fundamental conceptual distinction that used to be reserved for technical whizzes and now finds its way increasingly into everyday conversations.ANALOG vs. DIGITAL is a fundamental conceptual distinction that used to be reserved for technical whizzes and now finds its way increasingly into everyday conversations.
ECHO ON vs. ECHO OFF has to do with whether the characters you type are echoed onto the screen. Depending on your computer, you might find that when you type, each letter is double-typed; if so, you turn ECHO OFF. If you are typing and nothing appears on the screen, then you must turn ECHO ON.
See Chapter 14 of this book titledNetworks & Telecommunications for more info and samples!
Who creates these things? Sometimes teenagers and sometimes adults, but only rarely do they get caught. A computer virus can be defined as a clever computer program that does something strange to your computer in some situations and spreads to other files and disks in the same machine. If you insert a floppy disk into a virus-contaminated hard drive, the chances are good that the virus code spreads to your floppy. Now you take your disk and bring it somewhere and the virus spreads to another hard drive. Electronic bulletin boards on modems can occasionally be sources for viruses spreading.
Now for the good news. Most computer viruses are benign and do not harm your computer. Many people react to computer viruses as if these stupid annoyances are more important than the national problems of drugs, homeless people and AIDS. Many people use viruses as excuses for everything that goes wrong that can¹t be figured out. ³My printer doesn¹t work at times ‹ must be a virus² says one person who hasn¹t learned to use the SELECT button. ³Sometimes when I print, I get extra spaces and incorrect margins because of those viruses² says another intermediate user who needs more instruction on TABs.
To test this out, we created a one inch square using Photoshop and found that it took 7,528 bytes to store the 8 bit color version and 14,027 for the 16 bit color version. Since there is other info stored by Photoshop, this validates the above theoretical discussion. The 1 bit version consumed 3,125 bytes which suggests about 2K to 3K of overhead using by Photoshop.
Here is the summary which we have then extended to a 2 and 3 inch square; don't forget the fact from gardening literacy that when you double the length and width of a garden, you have to multiply its area by 4!
If we work at 150 PIXELS PER INCH, then each number is quadrupled:
If you are connecting Macs, the type of wire can be standard phone wire (2 pair or 4 wires) in which case we say we have a LOCALTALK LAB (which only uses 2 of the 4 wires). Or we use one of many better types of wire in which case we say we have an ETHERNET LAB. Data travels via localtalk at 30K per SECOND (230,000 bits per second), or via ethernet at 1.25 MEG per SECOND (10 million bits per second) which is about theoretically 40 times as fast (only 20 times realistically). In either case, the typical language we would use in that lab would be called Appletalk. One of many other network considerations is that all Macs are localtalk ready, while only Macs such as the Quadra 610 and beyond are Ethernet ready. Thus in an Ethernet lab you need to add an extra interface card or external SCSI box to each older Mac (about $200 per station) or a transceiver for each new Ethernet-ready Mac (about $70 per station).
On a Mac network, you can share files, printers, CD-ROM drives and even modems. Several companies (such as Shiva) make a networkable modem to let all the Macs on a network access one central modem that might support 1 to 8 phone lines. Additionally, it is possible via software like AppleTalk Remote to dial in to the network from an outside location. In this case, what you see from home is identical to what you would see in the lab, except you are running at a slower speed. Even if your modem is 14,400 baud, this means files are transferring at 1,800K per second, 1/16th of Appletalk!
A relatively new and very exciting way to turn a picture into a computer graphic involves PHOTO CD technology. We use a local store which charges about $20-$25 to develop a roll of 24 prints plus put the 24 images onto a photo CD. To hold costs down, you need to do this when you develop the prints; the cost for negatives, slides or prints (as opposed to a roll of film) is $2-$5 per item. You can play your photo CD on most new Mac or IBM computer CD players (must be photo CD compatible) or on a photo CD player attached to your television. Each CD (up to 650 meg) holds about 80-100 images stored in multiple formats including 24 bit color!
On the other hand, DIGITAL means that the variations have been converted into discrete numbers, with a definite step from one to the next. DIGITAL devices are not just watches. Musical compact disks contain magnetic 1¹s and 0¹s in the grooves, so that the music is in effect coded and digitized; therefore we say
that old-fashioned records are ANALOG while CDs function as DIGITAL devices. VCR technology is ANALOG while LASER DISCS are DIGITAL.
MODEMS: The MODEM allows your computer to communicate via the telephone with other systems.
Sometimes the MODEM is the size of a small box, sometimes it is a board that fits inside your computer unit. The acronym MODEM stands for MOdulator DEModulator. Typically the MODEM box has one cable connected to your computer. A standard phone cable attaches from the MODEM to the phone jack; additionally, you can usually plug in a standard telephone into the MODEM, allowing you to use the telephone line for either voice or data communications. Once your computer is hooked up via MODEM to your phone line, you can communicate with another computer via its MODEM. Sometimes this setup is used to send documents back and forth. More common is the desire to access a huge database of information stored on that computer¹s disk drive, such as the Internet, America Online and Prodigy.
When using a MODEM, the two computers do NOT have to be the same kind. However, it is crucial to have some kind of MODEM SOFTWARE that facilitates the transfer of information. For example, on the Apple II, Beagle Brothers Software makes a telecommunications package called TimeOut TeleComm that becomes part of Appleworks. On the Mac and IBM, Microsoft Works and ClarisWorks include communications as one of the modules along with the other tools. For each machine, there are at least a dozen companies that publish this kind of software.
There are many buzzwords regarding MODEM use that tend to make things sound more complicated for beginners: 8 bits vs. 7 bits, number of stop bits, odd or even parity, xon/xoff handshaking, terminal type. The important concept is to realize that you simply have to match the service that you are dialing. For example, the manual might instruct you to set your software to VT-100, 1200 baud, 8 bit data size, 1 stop bit, no parity and xon/xoff handshaking. You match these settings with your software and you are all set to dial. Even though each of the characteristics means something technical in terms of how the data is transmitted on the phone, the typical user need not be concerned with the details. What's important is the MATCHING CONCEPT -- your settings need to match those of the other party.However, two of these concepts will need to be understood by the average user: BAUD RATE and ECHO ON/OFF.
BAUD RATE means the rate at which the data travels on the phone line. Baud means bits per second, so a BAUD RATE of 300 means 300 bits per second or approximately 37.5 characters (bytes) per second; this is under 1 line of text per second. Similarly 2400 baud means 2400 bits per second i.e. 300 bytes or 6 lines per second. In the older days, modems were between 300 and 2400 baud and cost over $300. Now 9600 baud modems are under $100 and 14,400 baud modems are under $200. If you have a 9600 baud modem but the service you are dialing is only 2400 baud, you can¹t use the faster rate. It is interesting to note that some modem services charge a higher fee for faster rates, e.g. CompuServe used to charge $6 per hour for 2400 baud and $12 per hour for 9600 baud.Going ON-LINE involves MULTIPLE COSTS.
Cost #1 is the modem itself, perhaps $50-$200. If you need to buy a communications program, then cost #2 is another $50-$100. However, this program is frequently bundled with the modem. Software like Microsoft Works or ClarisWorks includes communications which is good enough for most non-techies.On the Mac, SHAREWARE SOFTWARE like ZTERM by David Alverson
(513-398-2586 or davea@xetron.com) offers ZMODEM file-transfer protocol and not just XMODEM, YMODEM and Kermit. Cost #3 might be to gain access to services. Most services (CompuServe, America OnLine, Prodigy) charge a flat fee per month or a per hour charge, typically $10 per month or $2 per hour. Increasingly, Internet access is being provided for free by universities and state organizations. For example, the University of Massachusetts (with its outstanding basketball team) recently began its UMASSK12 service (perhaps to lift the spirits of Celtic fans suffering in 1994). If you are not located near a big city, you will accumulate cost #4 ‹ long distance charges from the phone company (which charges the same rate for voice or data). Make sure your phone line is designated for unlimited local calls! One school we know made this mistake and recently accumulated a $800 phone bill for several months of local phone calls. And then there is the installation and monthly cost of each new phone line you may need. This potential cost #5 can completely dwarf the other costs, e.g. $30-$60 per month!
MIDI stands for MUSICAL INSTRUMENT DIGITAL INTERFACE.
A MIDI connector plugs into your computer, typically from an electronic keyboard. Some keyboards are MIDI compatible, though cheap ones are not. Once you have connected your music keyboard to your computer, you can enter notes on the screen via the piano keyboard.
The minimum cost used to be about $300-$400 for the midi-compatible piano keyboard and $75 for the midi-interface external cable which connects from the computer's modem port to that keyboard. Then you need music software that has midi features; this can range from $50 to $600. The Miracle Piano Teaching System for about $200 consists of a keyboard and cables to your computer. The software gives you rooms for musical practice, studio work for ³mixing,² a classroom for instruction and a musical arcade drill and practice area. The Miracle Piano is midi-capable with a hookup costing $75!
CD ROM PLAYERS are able to read computer compact discs that look and function like musical compact discs.
A computer compact disc typically holds up to 650 megabytes (over 1/2 a gigabyte). This is the equivalent of about 4200 Apple 5.25" 140K floppy disks or about 1800 IBM 5.25" 360K disks. In basketball terms, this represents a stack of typewriter pages the height of the Boston Garden. Computer CDs are read-only; you do not record onto them, but only get information from them. New CD hardware for under $2000, however, lets you make your own CDs. For a few hundred dollars, various service companies will make a CD from your data. At Noble & Greenough School, for example, we hope to make our Where's Bakes? CD chock full of audio, graphics and quicktime movies.
VOICE DIGITIZERS allow you to record voices and sounds and do something like word processing on the recorded sound.
The package usually consists of a microphone and software that turns the sounds into 1¹s and 0¹s to be stored in RAM and on a disk. Once the sound is turned into a wave form on your screen, the software may allow special effects such as reversing the sound, amplifying it, making it reverb as if it comes from outer space or a concert hall.
A LASER DISC PLAYER looks like a VCR and plays video and audio images.
While some people use their laser disc player for movies and enjoy the improved quality, the real power of a laser disc can be exploited when hooked up to a computer. A software package running on the computer can contain many clever, organizational features. For example, your laser disc may contain thousands of frames from an art gallery and your software lets you search by style, artist, chronology or theme, providing you with close-ups when desired. Or your laser disc may contain thousands of frames of news footage on the Middle East and the software allows you to retrieve in selective ways so you can make your own documentaries.Encountering COMPUTER VIRUSES is now a common experience for many regular users.
To simplify for the beginner, one might say that a COMPUTER VIRUS is like a special device inserted into the carburetor of a car by a dishonest mechanic. The mechanic puts this device into your car which alters the gas mixture when you travel exactly 33 MPH so that 16 rings of smoke come out of the exhaust pipe. Not a nice mechanic you say? Well, you¹re probably right, but we don¹t have the analogy for a computer virus yet. The main characteristic of the computer virus is that it is a set of instructions put onto a disk such that when this disk comes in contact with another disk, the set of instructions copies itself to the other disk. It¹s similar to the car mechanic wiring your car so that whenever you park next to another car, the nasty carburetor problem in your car jumps and spreads to the next car. Yuck! Now we¹ve got the equivalent of a computer virus. For under $100 on most computers, you can buy a reliable, relatively easy virus COMMERCIAL program (e.g. SAM, Norton AntiVirus, Central Point AntiVirus) that will disinfect existing hard disk drives and prevent subsequent viruses from coming back. A popular PUBLIC DOMAIN program for the Mac called Disinfectant is widely available via modem and catalogs.
See chapter 9 in this book for more details on Disinfectant. 
Trying to understand the size of COMPUTER GRAPHICS FILES becomes an excellent exercise in synthesizing the concepts of bits, bytes, kilobytes, megabytes, and pixels.
First, we begin by the fact that the screen resolution is generally 72 pixels per inch and so a one inch square would contain about 5,184 pixels (72x72). If you are working in one-bit color such as traditional Hypercard, then each pixel can be only black or white so it occupies one bit that is either 1 or 0. Therefore, 5,184 pixels would occupy 648 bytes (5,184/8) which is under 1K.
If you are working in 8-bit color then each pixel can be one of 256 shades of gray or 256 colors (the number 256 is 2^8th power or 2x2x2x2
This means that 5,184 pixels would occupy 5,184 bytes or approximately 5K.
And if you are working in color then each pixel can be one of 65,536 colors (the number 65,536 is 2^16th power or 256x256). This means that 5,184 pixels would occupy 10,368 bytes, since each pixel would require 2 bytes to store its color choice out of 65,536.
And finally if you are working in 24-bit color then each pixel can be one of 16,777,216 colors (the number 16,777,216 is 2^24th power or 256x256x256). This means that 5,184 pixels would occupy 15,552 bytes, since each pixel would require 3 bytes to store its color choice out of 16,777,216 possibilities. By the way, the best way to picture 16.7 million colors is to think of mixing 256 shades of each primary color.
And so that 3 inch square, 24 bit color picture would consume about 10% of a high density disk. And this is all at 72 PIXELS PER INCH which is the screen size and a low resolution for anyone doing serious graphic art!
picture size 1 bit color 8 bit 16 bit 24 bit
1 inch square 2/3 of a K 5K 10K 15K
2 inch square 2.7 K 20K 40K 60K
3 inch square 8K 45K 90K 135K
And so that 3 inch square picture would consume about 40% of a high density disk. If we choose to work at 300 PIXELS PER INCH, then we get
picture size 1 bit color 8 bit 16 bit 24 bit
1 inch square 2.7K 20K 40K 60K
2 inch square 10.8K 80K 80K 240K
3 inch square 32K 180K 360K 540K
That 3 inch square picture now consumes almost an entire high density disk!
picture size 1 bit color 8 bit 16 bit 24 bit
1 inch square 6K 45K 90K 135K
2 inch square 24.3K 180K 360K 540K
3 inch square 72K 405K 810K 1215K
A COMPUTER NETWORK has increasingly become a basic part of computer literacy.
To create this network, we begin by physically cabling the various computers (let's call them A,B,C,D and E) together, either as a DAISY CHAIN (one wire from A to B, another wire from B to C, another wire from C to D, and a fourth wire from D to E) or as a STAR (each wire from A,B,C,D and E runs directly to one central closet). A SCANNER looks like a photostat machine and transfers a graphic from a photograph or drawing onto the screen
.
In effect, the scanning software digitizes the picture into 1¹s and 0¹s to be stored in the RAM chip and subsequently onto the disk drive. Traditional Hypercard scans involve each pixel being either black or white (1 BIT COLOR) and are poor quality like most of the pictures in this book. GRAY SCALE means that each pixel can be one of 256 shades of gray (the pictures from Cooperstown Hall of Fame on the last page of this chapter, those of Noble and Greenough School in chapter 13 or the John Havlicek signature tie in chapter 16). 8 BIT COLOR means that each pixel is 1 of 256 colors. 16 BIT COLOR means that each pixel is 1 of 65,536 colors. 24 BIT COLOR means that each pixel is 1 of 16,777,216 colors. There are also hand-held scanners (bigger than the hand that Chris Ford may soon get) that you roll across the document to be scanned.
OCR SOFTWARE is an enhancement to the traditional scanner functions and allows you to turn a printed page of text into a word processed document that you can edit.
Without OCR software, your scan of a printed page would appear as a graphic. Using OCR software (which stands for optical character recognition), you can scan pages of a book like Drive by Larry Bird and turn Magic Johnson's words in the foreward into a word processed, editable text:
He will make the big shot or big play. Of all the people I play against, the only one I truly fear or worry about is Larry Bird. Whenever we play Boston, it's always in the back of my mind that no matter what the game situation is, Larry Bird can come back and beat us.
By the way, despite Larry's frequent hard drives to the basket, his book called Drive has nothing to do with computers!
There are also digital cameras such as the QuickTake camera (around $700) that let you take pictures for immediate transfer to a computer. The QuickTake comes with software for your Mac or IBM and a cable for transferring the images.
This one gray scale page took 11 minutes to print using a LaserWriter IINT (300 dots per inch)!