Max Learning's Digital Dozen

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1. bit   2. Byte   3. Code   4. Data   5. Program   6. Chip   7. CPU   8. RAM   9. ROM   10. Computer   11. Peripheral   12. System


Peripheral = attached device:
Printer, Disk, Monitor, Keyboard, Mouse, Modem, Port, Optical disc, Speakers.
Acronym--P=ad: PDMonK-MsMoPo-ODSpks

In English, the word peripheral (pur-IF-ur-ul) literally means outside or around, as in peripheral vision. In Computerese, a peripheral is any device outside or around a computer that attaches to the motherboard.

Avoid embarrassment! Do not pronounce peripheral as pur-IF-ee-ul. To help you remember the correct pronunciation, train your cat to purr if your friend Earl comes into the room: Purr if Earl!



Since this is a rather long section, I decided to give you the complete Peripheral Hardware (PHW) AcroMap first. You'll soon discover what each acronym means. Observe that after the P=ad:, there are nine peripherals on the spine and three sets of three ribs. Practice on scratch paper until you can sketch the entire map perfectly from memory. 


PHW Spine Acrostic
To memorize the spine of this AcroMap, imagine you are at your pad (apartment) and two visitors, P. D. Monk and Ms. Mo Po, arrive with their barking dog, Odee: Pad -- P.D. MonK -- Ms. Mo Po - Od speaks

Peripheral List

Click on the desired peripheral to learn about it.








Optical disc



Transfers computer output to paper.
AcroMap: DIL = Dot Matrix, Inkjet, Laser

Three types of printers are most used with today's computers.

Dot Matrix
How it works: Multiple pins strike an ink ribbon onto paper to make a pattern of dots that look like characters.
Class: Impact (ink forcibly applied to paper).
Speed: Measured in CPS (characters per second).
Advantages: Can print through multipart forms and carbon paper.
Disadvantages: Noisy. Lower quality than inkjet or laser.

How it works: Sprays electrically-charged droplets of ink, guided by electromagnets, onto paper to make a pattern of dots that look like characters.
Class: Non-impact (ink gently applied to paper).
Speed: Measured in PPM (pages per minute).
Advantages: Quiet. Near-laser quality at a lower price. Able to print color.
Disadvantage: Slower speed, lower quality than a laser. Ink may bleed (spread) on some papers.

How it works: A pulsating laser beam creates static dots on a rotating drum to make a pattern of dots that look like characters. Then, similar to a copy machine, dry ink powder clings to the static dots. Next, paper with the opposite static charge rolls over the drum and attracts the powder dots. Finally, the paper passes through a heating element that fuses the powder dots to the paper.
Class: Non-impact (ink gently applied to paper).
Speed: Measured in PPM (pages per minute).
Advantages: Highest speed. Best quality.
Disadvantage: Most expensive, especially if color printer.


Printer Connection
Like all peripheral devices, a printer must be electronically attached to the motherboard. This is usually done with a cable plugged into a parallel port daughterboard (See Port).


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Magnetically stores computer switch settings.
AcroMap: FHC = Floppy, Hard, Controller. 

The surface of a disk platter is coated with magnetic particles. Each of these particles is a tiny magnet with two poles: South and North. A disk drive, which is the machine that spins the disk, contains tiny electromagnetic read/write heads that can change the orientations of disk particles in one direction or the other to mirror a computer's Off/On switch settings. Since magnetic particles retain their orientation even when power is off, disk storage is permanent until deliberately changed or erased.

Read (load, open)
Previously-oriented magnetic disk particles generate an electrical current in the read/write heads, which signal the computer to reset its switches Off or On to match.
Write (store, save)
The computer stores RAM switch settings by signaling the read/write heads to realign magnetic disk particles to match.

Read: Imagine that a tiny helper inside your computer looks at the magnetic disk particles and resets the RAM switches to match

Write: Imagine the tiny helper looks at the RAM switches and magnetizes the disk particles to match.

Important: Saving a file to disk does NOT cause the file to leave RAM--its switch settings are merely copied to disk. Likewise, loading a file from disk does NOT cause the file to leave the disk--its switch settings are merely copied to RAM.

Floppy Diskette
A diskette is a thin, circular piece of plastic coated with magnetic particles. Diskettes are inserted and removed as needed from diskette drives. The original diskettes were housed in a softshell casing that you could bend, hence they were called "floppies." Even with the newer rigid, hardshell cases, we call them floppies because inside they still have a thin piece of plastic. In common usage, it's acceptable to use the shorter "disk" rather than "diskette." A Superfloppy, which requires a special drive, can hold hundreds of times more bytes than a conventional floppy. 

Avoid embarrassment. Do NOT refer to a hardshell floppy disk as a Hard Disk! The HD embossed on the diskette stands for "High Density."

Hard Disk
A hard disk is a metal platter, or a stack of platters, coated with magnetic particles. Most hard disk platters are permanently housed in a disk drive, although some hard drives have removable disk cartridges. Each platter surface has its own read/write head. Unlike a plastic floppy disk, metal doesn't stretch at high speeds, therefore, data can be placed much closer together, and the disk can be spun much faster than on a floppy diskette. Consequently a hard disk holds more data and works much faster than a floppy disk.

Hard Drive
Technically, "drive" refers only to the machine that spins the disk and contains the read/write heads. The term "disk" refers only to the platter itself. However, in common usage "drive" and "disk" are used interchangeably. For example, it's acceptable to say either "hard drive" or "hard disk."

Is the hard disk part of the computer?

Many people confusedly think so. In early computers the disk drive sat outside the computer's case and was plugged into it with a cable. As computer circuitry got smaller, the disk drives were moved inside the computer case, leading to the mistaken notion that disk drives are part of the computer, that is, the motherboard.

Remember, disk drives are peripheral devices that attach to, but are not part of the motherboard, as you can see in the next diagram. On the other hand, disk drives (and all peripherals) are part of a computer system, which we'll discuss later.


Disk Controller
As the name implies, the disk controller controls the disk drive. It consists of circuitry with preset switches that hold the control instructions. Controller circuitry may be mounted directly on the disk drive or separately on a daughterboard. A ribbon-like cable connects the drive to the daughterboard which in turn plugs into a slot on the motherboard. Most controllers are capable of handling two floppy drives and one hard drive which is sometimes designated as 2 FD/HD in computer advertisements.

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Displays input from the keyboard and output from the computer.
AcroMap: VC =Video Card  

A monitor acts as our "window" into the computer, showing us what's held in the RAM switches and on disk. When viewing text, a standard monitor can display 80 characters across by 25 lines down. This explains why you can't see a whole page of text (about 60 lines) at one time and must scroll up and down to view it. Some programs let you reduce the view to display more characters and lines, but they also appear smaller. A larger monitor can display more items at regular size.

There are two types of monitors most used with today's computers.

CRT (Cathode Ray Tube)
Looks and works like a TV picture tube. Electron guns shoot beams of electrons through a shadow mask (a piece of metal full of evenly-spaced holes) to a phosphor-coated screen which causes dots to glow.

LCD (Liquid Crystal Display)
A flat screen is embedded with a matrix of wires. Where electricity flows through two crossing wires a liquid crystal substance rotates and creates a dot. A backlit screen has a light behind it that provides sharper contrasts. An active matrix screen has a transistor at each junction and displays sharp, vivid colors. A passive matrix screen, also called dual-scan, looks dim by comparison. Because of low energy requirements, LCD screens are used primarily in Notebook computers where long battery life is desirable. But desktop models save space, run cooler, and require less electricity.

Video Card
Monitors are attached to the motherboard via a cable and a daughterboard called the Video Card (aka video adapter or video controller). Monitors have certain built-in capabilities, but the Video Card determines what is actually displayed.


A monitor works by displaying patterns of dots, called pixels (a contraction of picture elements) that look to us like data.
The more pixels that a monitor can display, the better the sharpness or resolution of the picture. Resolution is defined as the number of pixels across by the number of pixels down, for example, 640x480, 800x600, 1024x768. Video Cards are rated by the number of pixels they can generate.

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Used to type instructions and data into RAM.
AcroMap: FTCN = Function, Typewriter, Cursor, Numeric

In the earliest computers, switches were set by hand, one by one. Typing on the keyboard is the modern way to set switches. As you type, the switches in RAM are reset, sending a corresponding pattern of dots to the screen.

The keyboard can be divided into four main sections.

Function Key
Contains F-Keys to activate preprogrammed commands which vary by program.

Laid out in QWERTY (the top left alphabetic keys) format. Also contains special non-typing computer keys.

Cursor Movement
Contains arrow and other keys to move cursor (aka Insertion Point) around on screen.

Numeric Keypad
Contains 10-key numeric keypad for rapid entry by touch.

Combination Keys
With few exceptions, combination keys do absolutely nothing alone, but must be combined with a second key. Each different combination lets you perform a new command from the keyboard, multiplying the number of possible actions available from the keyboard. For example: Hold [Shift] and tap [Tab] to tab to the left.
Toggle Keys
A single toggle key acts like two keys, saving space on the keyboard. Pressing a toggle key once sets its feature on or off. Pressing it again reverses the setting. Example: Tap [Caps Lock] once for uppercase letters. Tap [Caps Lock] again for lowercase.
Space Character
[Spacebar]--Inserts ASCII code 32, the "space" character. In most programs, space characters are invisible to you and me but seen by the computer. We can "see" a space character only when it exists between two words, numbers, or symbols. On a blank-looking screen you can tell if there are space characters (as well as tab codes or return codes) by moving the cursor through them. You can NOT move the cursor through areas not filled with spaces.
Trap! Use [Spacebar] only to insert spaces. NEVER use [Spacebar] just to move the cursor because it inserts space characters that will have to be deleted later.
Tip: When using proportional fonts where letter widths vary, use [Tab] to separate columns of words, NOT [Spacebar].

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Used to move, draw, and select screen items.
AcroMap: PT-PT = Pen, Trackball, Pointing Stick, TouchPad
BrainAid: Your pet mouse's name is Putt-Putt.

A standard mouse has a rubber or plastic ball that, when rolled around on your desk, activates sensors that transmit the motion to a pointer arrow on the screen. When the arrow is pointing at an option on the screen a click or doubleclick of one of the mouse buttons located on top of the mouse activates the option. You can also move objects around the screen by holding down the mouse button and rolling (dragging) the mouse across your desk, releasing the button (dropping) when the object is where you want it.

There are four major mouse variations.

A mouse shaped like a pen. If it has a roller ball on the end, it can be used with a standard mouse pad. If it has a point on the end, it is designed to be used with an electronic drawing pad. A pen-shaped mouse offers a more natural grip for drawing.

A stationary upside-down mouse with its ball on top. You use your thumb or fingers to roll the ball and move the pointer. A trackball doesn't require much desk space and is commonly built in to portable computers.

Pointing Stick (aka Eraserhead)
It looks like a pencil eraser located between the G and H keys on a keyboard, primarily on portable computers. When you push the eraserhead in the desired direction, the mouse pointer moves accordingly. It doesn't require free desk space. Touch typists like it because you don't have to remove your hands from the keyboard. It's equally accessible to both right- and left-handed users.

A touch-sensitive pad, about 3 inches square. Dragging your finger across the surface causes the mouse pointer to move. You tap on the pad to click. It doesn't require free desk space and is commonly built into portable computers.


Mouse Connections
Dedicated--Some motherboards have a built-in mouse port.
Serial--Mouse plugs into an existing serial port (see Port).
Bus--Mouse comes with and plugs into its own daughterboard.


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Transmits files between computers via phone lines.
AcroMap: DAD = Digital, Analog, Digital

Sometimes it is desirable to transmit programs and data over long distances. Perhaps you need to send a report to your home office while you are traveling. Maybe you want to send a message to a friend or relative, or you need to download a copy of the latest device driver from the manufacturer.

If computers are located next to one another, a cable can be strung between them so they can, with the proper software, communicate back and forth. However, most computers are geographically separated. It would not be economically feasible or even legally possible for computer owners to run wires from their computers to every other computer that they wanted to communicate with.

Fortunately, an existing network of wires can be used to connect computers all over the world--telephone lines! But there's a problem: Computers transmit in digital pulse form, whereas the phone lines transmit in analog (AN-uh-lawg) wave form.

To send data over phone lines, the digital pulses must be MOdulated into analog wave forms. Then on the receiving end, the analog waves must be DEModulated into digital pulses. The device that performs these Digital-Analog-Digital operations is called a MODEM. A modem is required on each end of the transmission.

In the following drawing, the computer on the left sends 01 data pulses to its modem, which converts them into waves capable of being carried over the phone lines. On the receiving end, the procedure is reversed as the receiving modem converts the waves back into identical 01 pulses.

Transmission Speed
Modem speed is measured in bps (bee-pee-ess) or bits per second transmitted. Observe the lowercase "b" for bit. To get a rough measure of how fast a modem transmits characters, divide the bps rate by 10. For example, a 56 kbps modem transmits 56000 bits per second. Dividing by 10 yields roughly 5600 bytes. That is, in one second, the modem can transmit 5600 characters--about three full screens on an average-sized monitor.

Fax Modem
This is a modem that also has fax circuitry built in. With accompanying software your computer can act like a fax machine by converting onscreen data or a scanned-in document  into fax "picture" form, which can then be sent to a receiving fax machine or another fax-modem.

Digital Modem
Digital modems don't have to convert a computer's digital output into analog wave form, because they use special digital or cable TV transmission lines. They can transmit at much higher speeds than analog modems.

Modem Connections
Internal Modem--Actually a daughterboard that contains phone line jacks.
External Modem--Housed in its own box; plugs into serial (aka COM) port.


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Socket on motherboard or daughterboard.
AcroMap: S1/P8/U = Serial 1, Parallel 8, USB

Ports accept cables from a variety of peripherals. A cable is a bundle of wires with connectors that plug into ports. Here are three common port types.

Serial 1
A serial port/cable transmits one bit at a time. It's slower than a parallel connection, but reliable over long distances. Typical uses: modem, mouse, scanner.
Visualize a single wire with 0 and 1 bits traveling through it. Each group of eight bits makes a byte, but only one bit is ejected at a time from the end of the wire. (An actual serial cable can have from 9 to 25 wires.)

Parallel 8
A parallel port/cable transmits one byte at a time. It's faster than a serial connection, but unreliable over distances greater than about 25 feet. Typical uses: disk drive, printer. A bidirectional parallel port can both send and receive data which is useful for printer feedback For example, the printer could send a message that it's out of paper.
Visualize eight parallel wires each carrying 0 and 1 bits. Combining bits across the eight wires ejects one byte at a time. (An actual parallel cable can have 25 wires.)

Universal Serial Bus
A USB port is a high-speed alternative to parallel or serial ports. Whereas most ports can connect only a single device, a USB port, with an added hub, can connect and manage up to 127 devices.

Port Connectors
In general, male connectors have pins or other protrusions.
In general, female connectors have holes or other indentations.


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Optical disc
Holds programs and data on a compact disc.
AcroMap: CD/DVD = Compact Disc, Digital Video Disc


The standard CD is called CD-ROM, an acronym for Compact Disc-Read Only Memory. Observe the "c" in disc to differentiate it from magnetic disk with a "k." (Not everyone uses a "c.") A CD drive rotates a platter and reads programs and data from the bottom side (the side without the label or printing on it). The platter itself is round, made of plastic, and coated with a thin metallic layer.

CDs originated in the music world and provided clear, digital sound. Because you could not personally record to them, they were considered "read-only." When the computer industry adapted CDs to store programs and data, they attached the acronym ROM, which you know means Read-Only Memory. This was an unfortunate choice because ROM designates an electronic memory chip, whereas CD-ROM is used for storage (like a magnetic disk, except that CD-ROM is permanent).


To store a 1 bit, a laser beam, under computer control, burns a pit into one of the tracks in the metallic coating on the bottom of the platter. To store a 0 bit, the laser does not fire, leaving a land between pits. Once a CD becomes pitted it can't be changed, hence it is "read-only."

To read data, a soft laser light is shone on the platter surface. Lands reflect the light, signaling a 0 bit. Pits scatter the light, signaling a 1 bit. The signals are converted into electrical pulses which reset the computer's RAM switches to match.

X transfer rates
The base CD-ROM data transfer rate, designated as 1X, is 150 KB/sec.
A 2X CD-ROM would be 2 x 150 = 300 KB/sec.
A 4X would be 4 x 150 = 600 KB/sec and so on.

CD-R--A CD-Recordable drive/disc that can be written to one-time, primarily to archive large amounts of data. It may also be called a WORM drive because it's discs are Write Once, Read Many.

CD-RW--A CD-Read/Write drive/disc can record (write), erase, and re-record (rewrite) its platters. Instead of making physical pits, it creates reflective marks that can be removed by the laser. Speed is designated with three X rates. For example: 16x10x40x = 16x write, 10x rewrite, 40x read.
BrainAid: As it spins, a CD-RW wrr's. WRR = Write, Rewrite, Read.

CD-ROM vs. Magnetic Disk

  • A standard CD-ROM holds 650MB, much more than a floppy disk but less than most hard disks.
  • CD-ROM transfers data faster than a floppy drive but slower than most hard drives.
  • A CD-ROM platter costs far less than an equivalent stack of diskettes, which is why software companies prefer to sell you their massive programs on one CD-ROM instead of dozens of floppy disks. And it's much easier for users to install (copy programs to the hard disk) from one CD than from many floppies.
  • Unlike magnetic disks, a standard CD-ROM cannot be saved to or erased.

Digital Video Disc (or Digital Versatile Disk) will eventually replace CD-ROMs. DVD discs use shorter wavelength lasers that create and read more densely packed pits, a dual-layered recording surface, and both sides of the disc. They can hold up to 17 gigabytes of data.
DVD-R--Platter can be written to once.
DVD-RAM--Platter can be read, written to, and rewritten to.


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Play music, voice, sound from the computer.
AcroMap: SC = Sound Card

Sound Card
Most computers have a small internal speaker wired to the motherboard for producing warning beeps or various sounds. But to hear full-bodied music and voice from the computer requires a Sound Card with attached speakers. A Sound Card is a daughterboard with circuitry that processes and amplifies sound files.

DSP (Digital Signal Processor)
Programmable chip on the Sound Card that relieves the CPU of sound processing operations.

Speakers come in various forms.

Stereo Speakers
Two speakers on either side of computer.

Satellite Speakers
In a three-speaker system a larger subwoofer plays bass sounds; two smaller speakers (satellites) surround the subwoofer and play remaining sounds.

These tiny speakers fit on your head.

Tip: You can play music CDs without a sound card if you plug headphones (or self-amplified speakers) directly into the output jack on the face of the CD drive.

Converts voice, music, and other sounds into electrical signals sent to the sound card.


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