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Parts of the Computer

What is a computer?

A computer is a machine that computes. Webster's Seventh New Collegiate Dictionary defines a computer as "an electronic machine for performing calculations". Perhaps a better definition of a computer is a device that can sort information and through that sorting process perform basic arithmetic calculations and make choices among alternatives. We call these logical operations, but it is really a function of the immensely fast ability of the computer to sort through data.

A microcomputer is essentially a personal computer, either a desktop or a laptop and its peripherals. The microcomputer is smaller than the minicomputer or the mainframe computers. One could also say that a microcomputer is a computer on a chip. A chip is a piece of silicon with additional electronic circuitry components embedded in it. A microprocessor is a type of chip. Chips can be thought of as the basic building blocks of computers. Some, such as Intel Corp.'s Pentium CPU, are incredibly complex and can perform many functions. Others are simple and designed only to do one task. Also called an integrated circuit or a microprocessor.

An integrated circuit (IC) is apackage containing many circuits and pathways working together to perform a particular function or a series of functions. Integrated circuits are the building blocks of computer hardware. There are several levels of circuit integration denoting different IC complexities. The microprocessor, known as the central processing unit (CPU), that controls the computer. Today's microprocessors cram more than 1 million transistors into 1 square inch of space. Microprocessors are responsible for interpreting instructions gathered from input devices and transmitting the results to output devices. Though there are many types of microprocessors, the two main families in use are Intel Corp.'s 80x86 line, which includes the 486 and Pentium processors, and Motorola's 680x0 line, which is found in Macintosh computers.

The chip is composed of a wafer of thin silicon not too much larger or smaller than the dimensions of your thumbnail. The wafer of silicon contains an integrated circuit that performs the same function as millions of transistors or tubes in the older computers. Silicon (Si) is a chemical element that you can find on the periodit table. Silicon is found in sand, quartz and opal as the molecule of Silicon Dioxide, also called silica, which is formed from one silicon atom and two oxygin atoms. A pure silica chip is used for the substrate for etchings that form microelectronic circuits that form the computer processor.

Some laptop computers are begninning to be made with plastic instead of silicon as the major chip component. Silicon is very delicate and susceptable to cracking and breaking when treated roughly. Many people have cracked their silicon chips when they dropped their laptops. The new plastic material is more resilient and more forgiving. Plastic chips are less likely to fracture with rough usage.

Hardware is the physical computer equipment a tangible physical asset that you can touch. Microcomputers are composed of hardware and software. Software is the intangible part of the computer which is the ideas or instructions that are man-made, which are recorded on the magnetic media and other storage parts of the computer. A good analogy is to compare hardware with property, plant and equipment, such as, tables and chairs, and software with intangible assets, like patents and copyrights.

In order to perform the functions of a computer, all computers must have both the hardware to perform the instructions and the software which is the coded version of the instuctions which tell the computer hardware what to do. The listing of these instructions are often collected into one entity which we call a program. These programs or sets of instructions and their documentation are often referred collectively as software. We can only see software when we read it though the computer hardware. It only exists like the words on paper and only has meaning when taken in the context of the language in which it is written.

How does the microcomputer work?

The computer sends information in patterns of current through an Integrated Circuit. These patterns can be sent hundreds of thousands of times pr second as the currents go on and off. The speed at which the patterns can be transmitted is referred to as the clock speed of the computer. The clock speed is measured in MegaHertz (MHz), which means millions of cycles per second and is referred to as the frequency of cycles.

Computer chips are produced which have a megahertz rating from 4.77 (the speed rating of the original IBM-XT computer) all the way up to 450 MHz for the Pentium II chip. Computers are getting faster every day. The higher the number of megahertz, the faster the computer can process information and programs.

CPU

The Central Processing Unit (CPU) is the brain of the computer. The CPU handles two functions the arithmetic/logic function which is where the actual computing takes place, and the control function, which directs programming commands and information flows into and out of the computer. The collection of computer commands that operates the control function are included in the Basic Input Output System (BIOS) and the Disk Operating System (DOS) commands of the computer.

Basic Input Output System (BIOS) There are three main BIOS manufacturers: Phoenix Technologies, American Megatrends Inc. (AMI), and Award Software. Phoenix recently purchased Award but will continue to offer an Award product line. Bios are the instructions that control the basic input output systems of the computer. Many BIOS systems are upgradable either by replacing the chip on the motherboard or by using built in flash memory capacities in the BIOS chip.

Flash memory is an alternative to an advanced form of ROM (Read only memory) called EEPROM. One type of ROM is PROM which is programmable read only memory. This was further upgraded to EPROM which is erasable programmable read only memory. The EEPROM is electronically erasable programmable read only memory. Flash memory works in the same way in that the static permanent ROM is now able to be programmed electronically similar to the way you upgrade software by using a disk to upgrade the BIOS.

The Microprocessor

The microcomputer uses a microprocessor as its CPU. A microprocessor is a single integrated circuit. The Integrated Circuit is a complex collection of very small electronic components organized into a circuit that controls the on and off switches of the computer. The circuit is referred to as integrated because all of the components that need to work together are etched into a single silicon chip.

The on and off switches contained within the silicon chip form the basis for data storage and the basic computer code that the CPU can read and translate. These on and off switches allow the computer to process information. All computers do not use the same microprocessor. There are many different types of microprocessor that are manufactured by different companies.

Microprocessors are classified by the amount of active or free memory that they can access. This free or active memory determines the size of computer programs that the computer can process at the same time. Early computers were limited to 64 kilobytes (thousand bytes of information).
Microprocessor Development
Chip Code Microprocessor RAM Capacity Computer Brands
6502 8-bit 64 KB true Apple II, Atari 800, Commodore 64, early CPM computers
8088 8086 80286 16-bit 640 KB free memory IBM PC, XT & Compatibles, IBM PS/2 models 25, 30, 50, 60
80386 32-bit 640-KB free IBM PS/2 Model 70, 80
80486 32-bit 640 KB free IBM Clones
Pentium 64-bit 512 MB free PCs
Pentium II 64-bit 512 MB free PCs
Xeon 64-bit 512 MB free PCs
68000 32-bit 64 MB free Macintosh, Atari ST, Amiga
68020 32-bit 64 MB free Macintosh SE & II, Mega ST
68040 64-bit 4 GB free Amiga 3000, Atari TT, Macs

The American Standard Code for Information Interchange

The computer translates voltage within the integrated circuit. When the circuit is turned on the number one is read. When the circuit is turned off the number is read as zero (0). The code in the computer is based upon the binary code, a series of zeros and ones or on and off if you prefer. These are the same binary patterns that were invented with the punched cards of Jacquard and later used by Hollerith. The holes in the card represented ones and the unpunched areas represented zeros. The computer recognizes these patterns of zeros and ones and translates them into characters.

The code the computer uses is the American Standard Code for Information Interchange (ASCII). The computer uses the code in the same way that Morse Code is used to send messages save that the computer is much faster than this older communication methodology. The computer translates these patterns into characters, numbers, and symbols. Each on and off switch is refered to as a binary digit or a bit. The pattern of 8-bits or one byte represents one character, one number or one symbol. (8 bits = 1 byte = 1 character, number or symbol). ASCII code must be used for one computer to communicate with another.

ASCII Characters

The permutations and combinations of 8 on and off switches translates into 256 unique characters, which is the result when 2 is raised to the 8th power or 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2. In the chart below you can find some examples of the ascii code and its equivalent in decimal code and hexadecimal code. Decimal code is the code that we all use in everyday life. Decimal code includes numbers of base 10. The hexidecimal code uses numbers of base 16.

A hexidecimal pair is used to translate and code information from the 8-bit binary code because it to provides 256 unique characters, which is an exact match to the 8 digit binary code. The decimal pair only provides 100 unique characters. So the computer stores a single english character including numbers and symbols as information in 2 character hexidecimal code and translates it into 8 character binary code. The hexidecimal code equivalent is a convenient means for humans to analyze the binary code of the computer.
Character Binary Code Decimal Code Hexadecimal Code
(space) 00100000 32 20
+ 00101011 43 2B
0 (ZERO) 00110000 48 30
9 00111001 57 39
? 00111111 63 3F
A 01000001 65 41
B 01000010 66 42
a 01100001 97 61
z 01111010 122 7A

Bytes are used as a measurement of capacity. Computer capacity from memory or processing is very rarely one byte. Computers normally have thousands, millions or billions of bytes when when referring to external and internal memory storage. Below are a few examples of terms used to refer to many bytes.

Kilobyte (KB) = 1024 bytes of information = 1024 characters
Megabyte (MB) = 1 million bytes of information = 1 million characters
Gigabyte (GB) = 1 billion bytes of information = 1 billion characters
Terrabyte (TB) = 1 trillion bytes of information = 1 trillion characters

A megabyte (MB) is a common measurement of computer storage equaling 1,048,576 bytes. The figures are fequently rounded to 1 millino. Also called a meg. A gigabyte (GB) is approximately 1 billion bytes, or 1,000MB. One GB equals 1,073,741,824 (2 to the 30th power) bytes or 1,024MB, but these figures are typically rounded to 1 billion. Often used when measuring the capacity of hard drives or other storage devices. Also called a gig. Tera (T) is a prefix that stands for 1 trillion and should become commonly used for a terabyte when storage devices break this barrier soon. A terabyte (TB) is a unit used to measure a storage device's capacity. One terabyte equals 1,099,511,627,776 (2 to the 40th power) bytes. It is commonly referred to as 1 trillion bytes.

These concepts and terms are important to an understanding of how the computer operates, and give the user an ability to communicate with others about the features, procedures and problems of computers. For example, 2 KB is about as much memory as is required to save the information shown on a regular page of 8.5 by 11 inch paper typed single spaced with 1 inch margins. These terms will continue to be used throughout the following introduction to the microcomputer's hardware and software. Buses

In the physical world, buses move people from place to place. In the computer world, the bus takes bits of information from place to place. So buses in both worlds perform a similar function.

Information must get from the processor to other components in the computer; otherwise, the operator, computer components, and processor will not be able to communicate. A bus is an electronic pathway along which signals are sent from one part of the computer to another. Information moves through an Input Output Bus on the Motherboard to get from the processor to the other computer components that are not integrated within the microprocessor. Busses are also capactity dependent, and control whether a microprocessor can communicate with other computer components as quickly as the processor can process data. There are 8-bit, 16-bit, 32-bit, 64-bit and even 128-bit buses taht carry data from one computer component to another.

Some chips have buses with a smaller bit capacity than the processor bit capacity. Think of the processor and the bus as a highway. If you have a 32-bit processor chip working with a 16-bit bus. It is a little like taking 32 lanes of traffic and reducing the number of lanes down to 16 lanes of traffic. This reduction in the number of lanes of traffic is bound to cause traffic jams and slowdowns. For example, the 386 SX chip iw a 32-bit chip that uses a 16-bit bus. The processing of 32-bits of information is slow, but it inevitably slows down the chain of events when it has to pass that processed information on to the other parts of the computer 16-bits at a time. The 386 DX chip is a 32-bit processor that uses a 32-bit bus and there is less slowdown when passing the processed information onto the other parts of the computer. Similar things have happened more recently, with the Pentium and Pentium II bus on the slower chips. The slower Pentium II chips process information at speeds of up to 200 MHz along the 64-bit data path. The bus within the computer was limited to 33 to 66 MHz cycle speed and in some cases the data path was restricted to a 32-bit bus. The newer pentium II chips of the higher speeds, up to 450 MHz, utilize a 64-bit bus with a MHz speed of 100. So not only were the lanes being reduced to fewer lanes of informaion but the processing speed is slowed down as well within the bus. In these situations the increase in the speed of the processor does not significantly increase the overall speed of the computer. So the bus has to be sped up by increasing the MHz and the number of bits ("lanes").

Special electronic paths called buses route data and control signals between these chips and RAM and data storage devices such as hard drives, diskette drives, or compact disc, read-only memory (CD-ROM) drives. These buses are designed to simultaneously move groups of ones and zeros. In modern computers, 32 ones or zeros, called bits, can be moved at one time between the microprocessor and RAM. This is a 32-bit bus. Data moving to some types of expansion cards and internal components is routed to 16-bit paths.

Universal Serial Bus (USB) is designed to work with any peripheral device and make it hot swappable and auto configurable even with the computer turned on. The problem is speed. The current USB standard tops out at 12 Mbps speed.

Fire Wire (IEEE 1394) is the next generation proprietary bus technology being developed by Sony. The big advantage here is the ability to import and export video signals in very high resolution of the standard 525 lines. The reason Fire Wire can do this is the high data transfer speeds of 100 to 800 Mbps.

The microprocessor cannot process a lot of information at one time, so it needs an area in which to store information waiting to be processed and information which is the result of processing.

Internal Memory

Memory is the area where your computer stores data. Internal data storage is composed of Random Access Memory (RAM) and Read Only Memory (ROM). Data is permanently stored in ROM or temporily stored in RAM.

The computer's RAM may be composed of Dynamic RAM (DRAM) or Synchronous DRAM (SDRAM). DRAM is a type of random access memory that stores information for only a short period of time and must be refreshed (recharged or restored) by the computer every so often of the information is lost. DRAM is less expensive and faster than than Static RAM (SRAM) and is normally used as the main memory of the computer if you are using early or pre-Pentium computers. DRAM is alower than SRAM and SDRAM with a speed of about or 60 to 90 nanoseconds.

In 1998, Synchronous Dynamic random-access memory (SDRAM) became the type of internal memory used in personal computers for what we normally refer to as the "RAM" of the computer. The SDRAM was mounted on DIMMS. SDRAM is a type of memory that can run at much higher speeds than conventional Dynamic RAM (DRAM). The speed increase is achieved by synchronizing the memory with the computer's internal clock, allowing for speeds of up to 100 megahertz (MHz), at least twice as fast as some types of DRAM and up to three times faster than others. SDRAM has already been bypassed by central processing unit (CPU) speeds, now often in excess of 300MHz. SDRAM II doubles the speed of SDRAM by accessing memory on both the rising and falling edge of the computer's clock instead of just once per cycle. In musical terms, it is akin to playing a note on the up and downbeat. Even SDRAM will be surpassed by newer DRAM technologies, which can range from 600MHz to 1600MHz. Early in 1999, the speeds of SDRAM were at about 6 ns access time. For access time the smaller the number the faster the access. For Megahertz the larger the number the faster the access.

Access time is the amount of time it takes the computer to read data from the memory chip and a good measurement of a memory chipís speed, usually noted in nanoseconds (ns). Speed increases as the access time decreases.

Dual inline memory module (DIMM) are the same as two single inline memory modules (SIMMs) sandwiched together on one circuit board. SIMMs require pairing where the memory must be matched. One 16 MB SIMM must be balanced across the bus with another 16 MB SIMM. DIMMs transfer data on both sides of the circuit board, effectively doubling the bus. Pentium and Pentium II computers require memory modules to transfer data to the processor over a 64-bit wide bus. DIMMs fit that bill, letting you install a single DIMM instead of a pair of SIMMs. DIMMs need not be paired since they automatically double or pair the bus due to their design.

Extended Data Output (EDO) is a type of dynamic random-access memory (DRAM) that features a speed boost of up to 10% over normal RAM. The faster speed is achieved by memory chips that donít need to be refreshed as often as those in normal DRAM chips. The computerís memory controller must be built to recognize EDO chips. EDO chips are seen in the pre- and early pentium computers, just before SDRAM became popular.

Single inline memory module (SIMM) is a circuit board containing several memory chips. One 16 megabyte (MB) SIMM, for example, could contain eight 2MB chips. SIMMS are typically used on older PCs, especially 386- and 486-series computers. Some computers with Pentium processors also use SIMMs. DIMMs, which boast faster speeds, have replaced SIMMs in all Pentium II computers and most Pentium computers.

A cache (Pronounced cash.) is a bank of high-speed memory set aside for frequently accessed data. The term "caching" is used to describe placing data in the cache. Memory caching and disk caching are the two common methods used by PCs. Whenever data are accessed from or committed to main memory, a copy, along with the address, is saved in the cache along with the associated main memory address.

A memory cache maintains a list of frequently accessed data, complete with the address of that data. When the processor attempts to access an address, the cache checks its stores. If the memory cache holds the requested address (called a cache hit), it returns the data to the processor. If not (called a cache miss), a traditional memory access takes place. Disk caching works essentially the same way but uses conventional main memory instead of high-speed memory. Many microprocessors today have built-in memory caches, which are called primary or Level 1 (L1) caches. External cache memory also can be added, called secondary or Level 2 (L2) caches.

Static RAM or SRAM is often used for cache memory. SRAM is faster than DRAM because it does not require refreshing. SRAM will remember the information stored in the chip as long as the power to the chip is constant. Due to the higher quality of SRAM it is more expensive than DRAM. SRAM has speeds wthich are faster than 10 nanoseconds but will soon be superceeded by even faster RAM technologies.

Internal cache is cache memory of the L1 type which is located right on the microcomputer chip. External cache (L2 cache) memory is located outside the microprocessor chip either on the Pentium II daughter board or on the motherboard itself. When we talk about cache internal and external refers to the chip itself. When we are talking about the main memory of the computer or of any other computer components we speak of internal as on the motherboard and external as off of the motherboard connected to the board by a port, interface card or other bus device.

SIMM or DIMM memory fit into SIMM or DIMM sockets right on the motherboard. The memory chips are attached to these smaller SIMM or DIMM boards. Older computers actually plugged the RAM memory chips directly onto sockets located on the motherboard. Upgrading was more difficult because removing and plugging in the chips could bend and break the small metal connectors that looked like the legs of a centipede off of the bottom of the chip. DIMM snf SIMM boards and sockets made replacing or upgrading RAM easier and eliminated the need for special tools and equipment.

Read Only Memory, or ROM, is permanently burned into a computer chip or integrated circuit, and is therefore said to be permanent or nonvolatile. ROM cannot be erased or reprogrammed by the computer. The BIOS (Basic Input Output System) is one such a program. ROM is the other type of internal memory, and is located on the motherboard. Instructions are installed at the factory to help run the computer and perform diagnostics on the computer system. In come cases, application programs and programming languages are stored in ROM, but this requires that the ROM chip be replaced to update the software to new versions as they become available. Software updates occur frequently, sometimes several times a year. It is much more convenient to update software on a disk-based system that requires the replacement of the ROM chip.

MOTHERBOARD

The motherboard is the main board or chassis into which all other circuit boards are plugged. The motherboard is also where the microprocessor, floating point coprocessor, RAM and ROM chips are plugged, via sockets, or they are soldered right into the board. The motherboard contains the bus of the computer and has many layers of plastic fiberboard that have thousands of small wires running in them to connect the various components. The layers of board provide for many layers of printed circuit tracks. Al items contained on the motherboard are considered internal to the computer. The motherboard is considered by many to actually BE the computer, since it directs, through the bus, the functions of the CPU, RAM, and ROM. The main SLOTS on the motherboard allow for the attachment of INTERFACE and EXPANSION BOARDS, which communicate to other input/output devices which are external to the motherboard (external devices) and expand the capabilities or features of the computer by adding more memory, clock battery, graphics, and others. Also contained on interface boards, or sometimes integrated into the functions of the motherboard, we find PORTS, which also connect to external input/output devices. The ports are physically male or female connectors with various standard pin and socket configurations, which connect to cables, which in turn connect to the external devices.

Ports are divided into serial ports, parallel ports, game ports, trackball ports, bud ports, external disk drive ports, direct memory access ports (DMA), scanner ports, and others. The most important ports to our discussion are the serial and parallel ports, which connect to printers, modems, mice, fax devices, etc.

INPUT/OUTPUT DEVICES

Input/output devices, or external devices, include disk drives (also called secondary storage devices), modems, printers, monitors, keyboards, mice, and others. "External" means that the device is external to the motherboard, but not external to the case that houses the motherboard. For example, disk drives are considered external devices even when housed within the main "CPU case" of the computer, because they do not reside or plug directly into the motherboard.

EXTERNAL OR SECONDARY STORAGE DEVICES

Secondary storage is used to store programs and data in a more permanent and less volatile fashion. The most popular secondary storage is MAGNETIC MEDIA. Magnetic media is material (plastic, metal, porcelain, etc.) coated with iron oxide (also called ferric oxide) to store information in the binary code via binary alignment of the magnetized ferric oxide surface.

External storage is cheaper than internal RAM or ROM based software, and it also has the advantage of being less volatile. A disk drive that uses magnetic encoding does not lose its memory when you turn off the computer system, or when the power fails. Magnetic storage only loses its information if the disk becomes damaged by misuse or worn out by continued use. External storage is therefore a more permanent storage then RAM.

Disk-based storage accesses data in a random fashion, similar to internal RAM, because it is able to find the data wherever it is on the disk from an index, and retrieve it without looking through the unwanted data. A tape drive or record requires that you move along the tape or record until you get to the location that you want.

Disk-based storage can be written to, erased, and read. ROM cannot be written to unless a special device is used to "burn" out the old information and "burn" in the new. The process is expensive and may result in the loss of function to the ROM.

The disk drive light, which is located on the front panel of the device, will indicate when the computer is reading or writing information to the disk or tape. NEVER ATTEMPT TO REMOVE A DISK OR TAPE WHILE THE LIGHT IS ON, BECAUSE THE DISK AND/OR DISK DRIVE MAY BECOME DAMAGED.

Magnetic disks can be damaged if they are not handled with care. Once damaged the data will probably not be recoverable; programs will not run at all or will be so damaged that any utility is lost. Due to the volumes of information contained on the disk, which have been created by thousands and millions of keystrokes at a keyboard, you want to be careful with magnetic media.

KEEP MEDIA AWAY FROM DUST AND SMOKE. Place the disk in a jacket cover or box when not in use. Store away from pencil sharpeners, ashtrays, drinks of any kind, and food. Graphite from pencils and rubber from erasers cause dust which may damage the diskette.

KEEP MEDIA AWAY FROM MAGNETIC FIELDS. Be aware of magnetic devices in the work place. Keep floppy disks away from magnetic paper clip holders, speakers (boom box, tape recorders, CD players, etc.), bell-ringing telephones, hard and floppy disk drives, the computer monitor, magnetic key chains, batteries, magnetic screwdrivers, transformers, and any type of electric motor.

KEEP MEDIA AWAY FROM EXTREME TEMPERATURES. Store in temperatures between 50 to 120 degrees F (10 to 52 degrees C). Media should be at room temperature before using it.

KEEP MEDIA AWAY FROM EXTREMES IN HUMIDITY. In humid weather, water can condense on diskettes. On the other hand, very dry air, while it should not damage the disk, may make the media very brittle.

HANDLE MEDIA WITH CARE. Keep food and drinks away from floppy disks and the computer work place. Do not pile other items up on floppy disks. Do not use floppy disks for bookmarks. Do not bend or fold floppy disks. Do not open the shutter on the disk. Do not write on the disk with a ballpoint pen or pencil. The graphite in the pencil and the downward pressure of the pen and pencil may score and damage the surface of the diskette under the cover. DO use a felt tip pen when writing on a disk label, or fill out the label before applying it to the disk.

DISK DRIVES

Disk drives are the most common secondary storage device. Disks in these drives store programs and data to be LOADED later into RAM to be processed, and are also used to SAVE data from RAM. Remember, RAM is volatile and data will be lost when the computer is turned off, if not saved to a disk first. There are floppy disks and hard disks that come in various capacities. Floppy disks get their name from the thin, flexible mylar plastic disk inside the outer case. The floppy disk case often has a sleeve inside that cleans and protects the disk surface.

All disks have a formatted and unformatted capacity. The double-sided, double density, micro disk has a one-megabyte unformatted capacity and a 720-kilobyte standard IBM formatted capacity. The other 280 kilobytes are taken up by the formatting instructions on the disk. Disk formatting instructions define the limits of the tracks and sectors on the disks that will hold the data. The definition of the location of the data on the disk by "numbered" or identified sectors and tracks allows the computer and disk drive to locate the information in random fashion. The disk first looks up exactly where to retrieve the data on the disk directory or File Allocation Table (FAT), and then the read-write head can be positioned quickly and accurately to retrieve that exact piece of data immediately.

All floppy disks have the same basic anatomy or structure. Each floppy disk has a protective plastic jacket. The disk has a hole in the jacket and either several (hard-sectored diskette) or one (soft-sectored diskette) corresponding hole in the disk itself. The timing hole is read by one of the electric eyes contained within the disk drive itself. The timing hole indicates to the disk drive the beginning of the track (soft-sectored) and sectors (hard-sectored) on the diskette. A 360-kilobyte double sided, double density diskette has 40 tracks per side, 9 sectors per track, and 512 bytes per sector, or 368,640 bytes (characters) of storage capacity per disk.

All floppy disks have a write-protect feature. An electric eye within the disk drive is placed so that it can see if the notch on the mini diskette or the window on the micro diskette is open or closed. On the mini disk, a tab of metallic tape is used to close the notch and occlude the light path of the electric eye. On the micro disk a little plastic chip is moved into position to occlude the window. The plastic chip is similar to those in plastic sliding hand puzzles. On the mini disk, if the tape is on the notch, the disk cannot be written to, nor can the disk be erased or formatted, unless the disk drive is defective. When the tape is on the notch, the disk is said to be WRITE-PROTECTED. When the notch is open, the disk drive can READ and WRITE to the disk.

All floppy disks are placed in the disk drive with the label side up, with the write-protect notch or window in the right bottom corner, and the shutter or data access opening to the from of the disk. The label side of flexible disks is also the top of the disk. The top of flexible disks is smoother than the bottom. The bottom of the mini disk is where the front and back edges of the flexible plastic protective jacket are heat-sealed. The bottom of the micro disk has a circular opening, so that the metal hub can be engaged by the by the disk drive spindle hub so that the disk can turn within the disk drive.

Floppy disks must be fully inserted into the drive until you feel a slight click as the mechanism of the drive engages the disk correctly. Floppy disks are engaged by the disk drive mechanism when the door is closed. Some drives have a drive door mechanism that manually closes with a lever. Other drives close automatically when the disk is pushed into the drive completely. The disk is ejected from the drive with a spring mechanism when the disk drive button is pushed to eject the diskette or the lever is moved to return the disk drive door to the open position.

Additional reading:

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