What is a Computer?
Content
What is a Computer? Merriam-Webster defines a computer as, “a programmable, usually electronic, device that can store, retrieve and process data.” This definition, though technically correct, doesn’t tell us much about practical computers. To be more specific, computer systems are made up of three general elements: Hardware – the electronic components that make up the physical machine. These devices provide data input, storage, processing, and output. Software – the instructions that control the hardware in order to implement data processing. These lists of instructions, called programs, are stored on the computer in electronic form. Data – the facts and figures that are processed by the software and hardware to produce a useful output. Data is also stored and processed in electronic form. In the remainder of this article, we’ll break down each of these elements so that we can better understand what a computer is and how it works.
Figure 1: Laptop Computer
Figure 2: Desktop Computer
Types of Computers Computers can be categorized in many different ways. One possibility is to sort them based on their function. The desktops and laptops (see Figures 1 and 2) that we most often associate with the word ‘computer,’ are powerful multipurpose computers that can perform many different tasks, limited only by the software applications installed on them. Even more common are special-purpose computers designed to accomplish a specific task. We encounter many examples of this type of computer every day. Some of the more common special-purpose computers are found in automobiles, appliances, digital cameras, cell phones, MP3 players, and GPS systems. Can you think of any others?
Microwave
Camera Cell Phone
MP3 Player
GPS
Figure 3: Special Purpose Computers
Computers can also be categorized by processing power and how many users they are designed to support at one time. The most powerful computers are called supercomputers. These computers handle very large databases and can perform an enormous number of calculations for scientific and engineering applications. For example, supercomputers are used to make weather predictions. The fastest supercomputer today is the IBM Roadrunner. The best-known builder of supercomputers is Cray Research.
Figure 4: Cray Supercomputer
Figure 5: IBM Roadrunner
Mainframe computers are large computers typically used by business organizations for bulk data processing, such as consumer statistics and financial transactions. Mainframes are designed to efficiently process very high volumes of input and output. Mainframes are also used in centralized computing environments, where a single large computer does the processing for several hundred users. Each user accesses the mainframe using a ‘dumb terminal’, which is just a monitor and keyboard without any processing capability. As desktop computers and network servers have gotten more powerful, they have begun replacing mainframes in many situations.
Figure 6: IBM Mainframe
Minicomputers are basically scaled down mainframes. They are used by smaller businesses with fewer users.
Figure 7: IBM AS400 Series Minicomputers
In terms of the number of users accessing a machine, desktops and laptops are known as ‘personal computers’ or PCs. PCs are designed to support only one user at a time. PCs are occasionally referred to as ‘microcomputers’. Hardware As strange as it may seem, all the different computer types we have discussed work basically the same way. They all use the same functional building blocks. Those building blocks are input devices, a processing unit, a memory unit, storage devices, output devices, and communication equipment. The block diagram, shown in Figure 8, shows how the blocks are interconnected and how data is passed through the computer. The arrows indicate the direction of data flow.
Figure 8: Computer Block Diagram
Figure 9: Desktop Computer
Look at the example of a desktop computer shown in Figure 9. If you had to point to the computer in this picture, what would you point to? Some might point to the monitor (screen) since that is what we look at when we’re using the computer, but the monitor is only an output device. The heart and brains of the computer is the big black box. This box, often called the system unit or system box, or simply the box, contains the central processing unit (CPU), the system memory, and the primary storage device. The monitor, keyboard, mouse, and speakers are known as peripherals (pe∙riph∙er∙als). On a laptop computer many of the peripherals are built in.
Power Supply
Disc Drives
Motherboard
Disc Drive
Figure 10: Inside the System Unit
Inside the system unit you will find a power supply, disc drives, and a motherboard. See Figure 10. The power supply converts the electricity received from the wall receptacle into a form usable by the electronic circuits that make up the hardware. The disc drives provide mass storage of programs and data. The motherboard is a circuit board that holds the central processing unit (CPU), memory, and expansion slots (among other things).
Figure 11: Expansion card
CPU
RAM Memory
Expansion Card
Expansion Slot
Figure 12: PC Motherboard
Figure 12 shows a better view of a different motherboard. The CPU is located beneath the cooling fan. Note the expansion slot. Expansion cards are plugged into an expansion slot to provide additional capability to the motherboard (See Figure 11). Typical expansion cards are communication adapters, such as modems (for accessing the Internet over the telephone line) and network interface cards (to connect the PC to a local network), and enhanced video adapters for better graphics. Note the expansion card that has been added to this motherboard. Expansion cards are sometimes referred to as ‘daughter’ boards. The RAM memory modules are also plugged into slots on the motherboard. A typical hardware upgrade for a PC is to replace small capacity memory modules with larger capacity modules.
Important Terms Before continuing with our discussion of computers, it is necessary to define a few technical terms used extensively in the computer field. Digital - The electronic circuits used in computers can only operate in one of two conditions – On or Off. They are therefore referred to as digital circuits and the information they process is called digital data. (The two possible digital conditions are more accurately described as ‘signal’ and ‘no signal’’. Off represents the ‘no signal’’ state, not a condition of being powered down.) Bit (b) – the smallest piece of digital data. When expressed numerically, a bit can only have one of two values – 0 or 1 (0 = Off, 1 = On). Byte (B) – 8 bits together. Word – 2 bytes or 16 bits.
When discussing computers, you often encounter very large numbers. To make such numbers easier to work with, it is common to express them using metric prefixes. Here are the most common prefixes, along with their symbols and values: Kilo (k)
1 thousand
Mega (M) 1 million Giga (G)
1 billion
Tera (T)
1 trillion
For example, instead of saying a hard disc can hold 1 trillion (1,000,000,000,000) bytes, we would say it can hold 1 terabyte, which would be abbreviated as 1TB.
The Central Processing Unit (CPU)
Figure 13: Pentium 4 Microprocessor
The CPU is the brain of the computer. All the data processing is done by the CPU based on instructions it receives from the programming software. The CPU is also called a microprocessor. A microprocessor is an integrated circuit that contains millions of microscopic transistors and other electronic devices. Figure 12 shows a Pentium 4 microprocessor built by the Intel Corporation. The Pentium 4 is approximately the same size as a single saltine cracker, although it contains approximately 125 million transistors. The most sophisticated microprocessors can have billions of transistors. Although several characteristics of the processor affect a computer’s performance, the one most often considered is its speed. The speed of a processor determines the number of instructions it can execute in a second. Processor speed is measured in Hertz (Hz). Typical speeds of modern processors are in the range of 2 – 4 GHz (gigahertz).
Memory Before beginning our discussion of memory, we need to define some new terms: write and read. In the context of computer memory and mass storage, a write operation sends data to the device for future use. A read operation retrieves data from the device for processing. Memory is the workspace of the CPU. It is a temporary storage area where the programs and data being operated on by the processor must reside. There are two forms of memory found on the motherboard: RAM and ROM. RAM (random access memory) can be written to and read from. ROM (read-only memory) can be read from, but not written to. RAM is volatile, that is, it loses all its content when the power goes off (either intentionally or unintentionally). ROM, on the other hand, retains its content when the power goes off, so it is referred to as non-volatile.
Figure 14: Memory RAM (L) and ROM (R)
RAM is referred to as main memory. Normally, when discussing a computer’s memory, it is the RAM we are referring to. RAM is measured in megabytes (MB) and gigabytes (GB). Most modern computers will have between 1 and 4 GB of RAM. The amount of RAM on a computer is one of the factors in how powerful the computer is. The more RAM it has, the better its performance will be.
Mass Storage Recall that RAM is volatile. Therefore a computer needs a place to store programs and data on a permanent basis. That is the job of the mass storage devices. These devices don’t lose their content when the power goes off. You may reasonably ask, “Since RAM is volatile, why don’t we just use a mass storage device in its place and not have RAM at all?” The answer is, mass storage devices are very slow compared to RAM. The processor runs so fast that if it had to wait on read and writes to mass storage, computer performance would be greatly reduced. We would get very frustrated waiting on the computer to finish even simple tasks. It is easy to confuse computer memory with mass storage. Both are used to store programs and data. However, they are not the same. Memory is short term, storage is long term. Before you start an application, such as a game, the program is kept on a mass storage device. When you start it, the program is copied to RAM for execution by the processor, but the original version is still safe and sound on the storage device. Any data created by the application will be temporarily written to RAM, but must be transferred to the mass storage device (a process known as saving) before the power is turned off. This is a critical point – if you are writing a research paper for your history class during a thunderstorm, save often. If the power goes off unexpectedly, you will lose all the work you’ve done since the last time you saved it.
Hard Drives The primary mass storage device on your computer is the hard drive (also called the hard disc). The hard drive is located inside the system unit and isn’t accessible without opening the box (see Figure 10). Storage devices on your computer are designated by letter, where each drive is assigned its own letter. The hard drive is almost always designated as drive C:. (Note the colon following the ‘C’. Drive letters are always followed by a colon.) It is possible for a computer to have more than one hard drive. There are no standard letter designations for these – they could be assigned any letter from ‘D:’ on up.
Figure 15: Hard drive
The capacity of the hard drive is one factor that influences a computer’s performance. The capacity of hard drives is measured in GB (gigabytes). A typical hard drive in a modern computer will have several hundred GB. Terabyte (TB = 1000GB) drives are now available.
Removable Storage Hard drives are typically mounted inside the system unit, and aren’t easy to remove. When you need portable data storage so that data can be used on more than one machine, moving a typical hard drive isn’t feasible. Portable data storage is also referred to as removable media storage. The most common removable media technologies are optical discs (CDs and DVDs), floppy discs, and flash memory. When referring to disc storage (either optical or floppy), there are two entities to be concerned with: the disc and the drive. The drive is permanently installed on the system unit. The disc is the removable storage medium. The disc is inserted into the drive for reading and writing then removed for travel. The disc can then be inserted into a similar drive on a different computer, making the data available to that machine. The terms drive and disc are often used interchangeably when referring to disc media. There two types of optical disc: the CD (compact disc) and the DVD (digital video disc). You are probably familiar with music CDs and video DVDs. However, these discs can also be used to store computer programs and data. DVDs have a much higher data capacity than CDs do and DVD drives can play video discs on your computer. Video DVDs can’t be played on a CD drive.
Figure 16: CD Drive
There are three types of optical drives based on their ability to write data to the disc. These types apply to DVDs, as well as CDs. CD-ROM – the data is stored on the disc during the manufacturing process and can’t be overwritten. Most software programs are distributed in this format. CD-R – the disc can be written to one time. Once written, it can’t be rewritten. Writing data to an optical disc is often referred to as ‘burning the disc.’ CD-RW – this disc can be written to then rewritten several times. The burning process is relatively slow, so CD-RW drives typically aren’t used to store data that changes often. In order to utilize the write capacity of an optical disc drive, you must also use the right kind of disc. CD-R discs can be burned once using either a CD-R or CD-RW drive. They can’t be rewritten, even with a CD-RW drive. CD-RW discs can be written once using a CD-R drive. If you want to rewrite an optical disc, you must use both a CD-RW disc and a CD-RW drive. An older removable media technology is called a floppy disc. Floppy discs store data magnetically. Compared to other types of removable storage devices, floppy discs were slow, low capacity, and unreliable. As better technologies were developed, floppy discs fell out of favor. Newer computer systems don’t come with floppy drives (they can be special ordered). However, this transition only occurred a few years ago and many computers with floppy drives are still being used today.
Figure 17: Floppy Disc and Drive
PC Peripherals In additional to the various devices found inside the system unit, computers also rely on equipment located outside the box. These external pieces of equipment are known as peripherals. Peripherals can be classified as input devices, output devices, or both. Input devices are those that provide data to the computer. Examples of input devices include the keyboard, mouse, game controller, and camera.
Keyboard
Mouse Game Controller
Web Camera with Microphone
Figure 18: Input Devices
Output devices are those that receive data from the computer. Examples of output devices include the monitor (screen), printer, and speakers.
Monitor
Printer Figure 19: Output Devices
Speakers
Connecting Peripherals Peripheral devices must be connected to the system unit with an electrical cable in order to pass data back and forth. The electrical connector on the system unit where the cable connects is called a port. Some peripherals use specialized ports. For example, the monitor uses a port called the VGA port. However, most peripherals connect to a USB (universal serial bus) port. The system unit will have several USB ports, a few on the front and more on the back.
Figure 20: Ports on the Back
Figure 21: USB Port and Cable
Flash Drives A non-volatile memory technology that has become popular is the last few years is known as flash memory. This is the same type memory used in digital cameras, cell phones, and MP3 players. Portable storage devices that use this technology are called flash drives. Most flash drives are designed to plug into a USB port on your computer (although there are other styles).
Figure 22: USB Flash Drive
For portable data storage, the USB flash drive can’t be beat. It’s fast, high capacity, durable, and inexpensive. The biggest problem with flash drives is losing them. Flash drives go by many different trade names, such as Pin Drives, Key Drives, Jump Drives, Thumb Drives, Memory stick, etc. But they are all based on flash memory technology, so are referred to generically as flash drives. Current flash drives range in capacity from 512MB – 16GB and typically cost between $10 and $50 dollars based on size. Software We previously defined software as, “the instructions that control the hardware in order to implement data processing.” Further, we said that the list of instructions to accomplish a particular task was called programming. These programs are saved on storage devices, such as hard drives, in an electronic format. When we open an application on our computer, such as a web browser or email, the program is copied from the hard drive to RAM for executing. Software can be divided into two broad categories: system software and application software. System software controls the basic operation of the computer, such as reading keystrokes from the keyboard, monitoring the movement of the mouse, outputting video information to the monitor, controlling the hard drive and sending jobs to the printer. Application software allows the user to accomplish a meaningful task, such as playing a game, writing a letter, finding a web page, watching a video, or balancing the checkbook.
System Software The system software running on a particular machine is called ‘the operating system.’ The operating system provides the interface between the user and the computer so the user can tell the computer what they want it to do. There are two basic styles of user interface: the command line interface (CLI) and graphical user interface (GUI, gooey for short). Command line interfaces are difficult to use because commands must be typed on the keyboard. The user must know what commands are available, what they do, and the proper format for entering them. (The proper format for entering a command is known as the command syntax.) When using a command line interface, the user must be highly trained prior to using the computer. Some well-known CLIs are MS-DOS, CP/M, UNIX, and the Windows command prompt.
Figure 23: The Windows Command Prompt
With a graphical user interface (GUI) the user communicates with the computer using a pointing device (such as a mouse). Using the mouse, the user points to an icon (a screen graphic that represents an application or command) on the screen and clicks the mouse button. Using a GUI interface, a user can begin accomplishing useful tasks on the computer after just a short tutorial on how to use the mouse. GUI operating systems are the standard today. The most popular are Windows and Macintosh.
Figure 24: Windows GUI
Application Software Application software is sometimes referred to as ‘productivity’ software. Applications are run by the operating system to allow users to accomplish meaningful tasks. Examples of typical applications would include word processors to assist the user in creating written documents, spreadsheets to help the user with repetitious calculations, presentation software to help the user create attractive slide presentations, web browsers to surf the Internet, games for recreation, and many more. Most operating systems come with some basic applications included. More sophisticated software must be purchased separately. For example, Microsoft Windows comes with a basic word processor called WordPad (Figure 25), a basic drawing program called Paint, a web browser called Internet Explorer (Figure 26), a calculator, several games (Figure 27), and more. However, the most popular business software, Microsoft Office, does not come with Windows.
Figure 25: WordPad
Figure 26: Internet Explorer
Figure 27: Solitaire
Data We previously defined data as, “the facts and figures that are processed by the software and hardware to produce a useful output.” For example, if we write a letter using a word processor application, the letter is the data we created. If you create a drawing in Paint, the drawing is the data. If you save a game so you can finish it later, the saved game is the data. After creation, data must be saved to a storage medium (hard drive, flash drive, etc.) to be used later. Always remember to save your data after creating it. If you close the application without saving, the data will be lost and is unrecoverable. Applications designed for use with the Windows operating system will warn you if you attempt to close the application without first saving your data.
Figure 28: Windows Save As Box
The data created using a particular application is only good for that application. For example, you write a letter using a word processor application. You save the letter then send it to a friend using email. The friend may not be able to open the letter if they don’t have the same word processor software you used. Most applications allow you to save your data in a generic format that will be compatible with similar applications, but you must remember to use this generic format. There will be more discussion on this subject later in the course. Turning it On To turn on your computer, look for a button with this symbol (this is the standard power button symbol) on the front of the system unit. Press and release it.
Figure 29: Power Button Symbol
You must also turn on the monitor. A common mistake on desktop computers is turning on either the system unit or the monitor, but not the other. This is an easy mistake to make, especially if the system unit is sitting on the floor. If you think the computer should be on, but the screen stays black, check to be sure that both the system unit and the monitor have been turned on. (This is only a concern with desktop models; laptops only have one power button.) You may recall that early in this discussion you were introduced to ROM memory. Not much was said about it at the time and you may have wondered about its significance. Well, the waiting is over. When you first turn on the system unit, RAM is empty because it is volatile (do you remember what that means?). If RAM were the only memory, the CPU wouldn’t be able to get the operating system off the hard drive. However, there is another section of memory called ROM. ROM can’t be easily written to, but it is non-volatile. ROM holds the basic instructions needed to get the computer started and the operating system loaded into RAM. The first instructions in ROM cause the CPU to execute a power-on self test (POST). POST checks RAM and several other critical subsystems, such as the keyboard, to be sure they are functional. Once the POST is complete and all the systems have checked out, the operating system is copied from the hard drive into RAM. At this point control of the computer is turned over to the operating system and we’re off and running. Boot Up The process just described to get the computer up and running is called boot up. There are two types of boot up: cold boot and warm boot. A cold boot occurs when the computer has been powered down and is turned back on using the power button. A cold boot includes the POST. A warm boot occurs when the system must do a restart after installing some types of software. In this case the reboot is initiated by the computer, not the power button (you can instruct Windows to execute a warm boot by using the Restart utility). A warm boot does not include the POST, but other than that, a warm boot and cold boot are the same.
Turning It Off Many people leave their computers running all the time. There is nothing wrong with that. But other people like to shut their computer off when not in use. DON’T turn off your system unit the same way you turned it on. The operating system needs to shut down the systems in an orderly fashion. The proper way to turn off your system unit is to implement the Shutdown utility in the operating system. It is okay to use the power button on your monitor.
Restart (warm boot) Shutdown
Figure 30: Windows Shutdown
One last tip. There is one situation when you will need the power button to turn off your system unit. If the operating system freezes up and will not respond to the keyboard or mouse, press and hold the power button for several seconds (pressing and releasing the power button won’t do it). The computer will power down. Wait a few seconds then press the power button again to turn the unit back on. Only use this procedure as a last resort. The operating system doesn’t like it and will run several diagnostic routines to be sure everything is alright before loading the operating system on the next boot up. Good luck and good computing!
Figure 1: Laptop Computer
Figure 2: Desktop Computer
Types of Computers Computers can be categorized in many different ways. One possibility is to sort them based on their function. The desktops and laptops (see Figures 1 and 2) that we most often associate with the word ‘computer,’ are powerful multipurpose computers that can perform many different tasks, limited only by the software applications installed on them. Even more common are special-purpose computers designed to accomplish a specific task. We encounter many examples of this type of computer every day. Some of the more common special-purpose computers are found in automobiles, appliances, digital cameras, cell phones, MP3 players, and GPS systems. Can you think of any others?
Microwave
Camera Cell Phone
MP3 Player
GPS
Figure 3: Special Purpose Computers
Computers can also be categorized by processing power and how many users they are designed to support at one time. The most powerful computers are called supercomputers. These computers handle very large databases and can perform an enormous number of calculations for scientific and engineering applications. For example, supercomputers are used to make weather predictions. The fastest supercomputer today is the IBM Roadrunner. The best-known builder of supercomputers is Cray Research.
Figure 4: Cray Supercomputer
Figure 5: IBM Roadrunner
Mainframe computers are large computers typically used by business organizations for bulk data processing, such as consumer statistics and financial transactions. Mainframes are designed to efficiently process very high volumes of input and output. Mainframes are also used in centralized computing environments, where a single large computer does the processing for several hundred users. Each user accesses the mainframe using a ‘dumb terminal’, which is just a monitor and keyboard without any processing capability. As desktop computers and network servers have gotten more powerful, they have begun replacing mainframes in many situations.
Figure 6: IBM Mainframe
Minicomputers are basically scaled down mainframes. They are used by smaller businesses with fewer users.
Figure 7: IBM AS400 Series Minicomputers
In terms of the number of users accessing a machine, desktops and laptops are known as ‘personal computers’ or PCs. PCs are designed to support only one user at a time. PCs are occasionally referred to as ‘microcomputers’. Hardware As strange as it may seem, all the different computer types we have discussed work basically the same way. They all use the same functional building blocks. Those building blocks are input devices, a processing unit, a memory unit, storage devices, output devices, and communication equipment. The block diagram, shown in Figure 8, shows how the blocks are interconnected and how data is passed through the computer. The arrows indicate the direction of data flow.
Figure 8: Computer Block Diagram
Figure 9: Desktop Computer
Look at the example of a desktop computer shown in Figure 9. If you had to point to the computer in this picture, what would you point to? Some might point to the monitor (screen) since that is what we look at when we’re using the computer, but the monitor is only an output device. The heart and brains of the computer is the big black box. This box, often called the system unit or system box, or simply the box, contains the central processing unit (CPU), the system memory, and the primary storage device. The monitor, keyboard, mouse, and speakers are known as peripherals (pe∙riph∙er∙als). On a laptop computer many of the peripherals are built in.
Power Supply
Disc Drives
Motherboard
Disc Drive
Figure 10: Inside the System Unit
Inside the system unit you will find a power supply, disc drives, and a motherboard. See Figure 10. The power supply converts the electricity received from the wall receptacle into a form usable by the electronic circuits that make up the hardware. The disc drives provide mass storage of programs and data. The motherboard is a circuit board that holds the central processing unit (CPU), memory, and expansion slots (among other things).
Figure 11: Expansion card
CPU
RAM Memory
Expansion Card
Expansion Slot
Figure 12: PC Motherboard
Figure 12 shows a better view of a different motherboard. The CPU is located beneath the cooling fan. Note the expansion slot. Expansion cards are plugged into an expansion slot to provide additional capability to the motherboard (See Figure 11). Typical expansion cards are communication adapters, such as modems (for accessing the Internet over the telephone line) and network interface cards (to connect the PC to a local network), and enhanced video adapters for better graphics. Note the expansion card that has been added to this motherboard. Expansion cards are sometimes referred to as ‘daughter’ boards. The RAM memory modules are also plugged into slots on the motherboard. A typical hardware upgrade for a PC is to replace small capacity memory modules with larger capacity modules.
Important Terms Before continuing with our discussion of computers, it is necessary to define a few technical terms used extensively in the computer field. Digital - The electronic circuits used in computers can only operate in one of two conditions – On or Off. They are therefore referred to as digital circuits and the information they process is called digital data. (The two possible digital conditions are more accurately described as ‘signal’ and ‘no signal’’. Off represents the ‘no signal’’ state, not a condition of being powered down.) Bit (b) – the smallest piece of digital data. When expressed numerically, a bit can only have one of two values – 0 or 1 (0 = Off, 1 = On). Byte (B) – 8 bits together. Word – 2 bytes or 16 bits.
When discussing computers, you often encounter very large numbers. To make such numbers easier to work with, it is common to express them using metric prefixes. Here are the most common prefixes, along with their symbols and values: Kilo (k)
1 thousand
Mega (M) 1 million Giga (G)
1 billion
Tera (T)
1 trillion
For example, instead of saying a hard disc can hold 1 trillion (1,000,000,000,000) bytes, we would say it can hold 1 terabyte, which would be abbreviated as 1TB.
The Central Processing Unit (CPU)
Figure 13: Pentium 4 Microprocessor
The CPU is the brain of the computer. All the data processing is done by the CPU based on instructions it receives from the programming software. The CPU is also called a microprocessor. A microprocessor is an integrated circuit that contains millions of microscopic transistors and other electronic devices. Figure 12 shows a Pentium 4 microprocessor built by the Intel Corporation. The Pentium 4 is approximately the same size as a single saltine cracker, although it contains approximately 125 million transistors. The most sophisticated microprocessors can have billions of transistors. Although several characteristics of the processor affect a computer’s performance, the one most often considered is its speed. The speed of a processor determines the number of instructions it can execute in a second. Processor speed is measured in Hertz (Hz). Typical speeds of modern processors are in the range of 2 – 4 GHz (gigahertz).
Memory Before beginning our discussion of memory, we need to define some new terms: write and read. In the context of computer memory and mass storage, a write operation sends data to the device for future use. A read operation retrieves data from the device for processing. Memory is the workspace of the CPU. It is a temporary storage area where the programs and data being operated on by the processor must reside. There are two forms of memory found on the motherboard: RAM and ROM. RAM (random access memory) can be written to and read from. ROM (read-only memory) can be read from, but not written to. RAM is volatile, that is, it loses all its content when the power goes off (either intentionally or unintentionally). ROM, on the other hand, retains its content when the power goes off, so it is referred to as non-volatile.
Figure 14: Memory RAM (L) and ROM (R)
RAM is referred to as main memory. Normally, when discussing a computer’s memory, it is the RAM we are referring to. RAM is measured in megabytes (MB) and gigabytes (GB). Most modern computers will have between 1 and 4 GB of RAM. The amount of RAM on a computer is one of the factors in how powerful the computer is. The more RAM it has, the better its performance will be.
Mass Storage Recall that RAM is volatile. Therefore a computer needs a place to store programs and data on a permanent basis. That is the job of the mass storage devices. These devices don’t lose their content when the power goes off. You may reasonably ask, “Since RAM is volatile, why don’t we just use a mass storage device in its place and not have RAM at all?” The answer is, mass storage devices are very slow compared to RAM. The processor runs so fast that if it had to wait on read and writes to mass storage, computer performance would be greatly reduced. We would get very frustrated waiting on the computer to finish even simple tasks. It is easy to confuse computer memory with mass storage. Both are used to store programs and data. However, they are not the same. Memory is short term, storage is long term. Before you start an application, such as a game, the program is kept on a mass storage device. When you start it, the program is copied to RAM for execution by the processor, but the original version is still safe and sound on the storage device. Any data created by the application will be temporarily written to RAM, but must be transferred to the mass storage device (a process known as saving) before the power is turned off. This is a critical point – if you are writing a research paper for your history class during a thunderstorm, save often. If the power goes off unexpectedly, you will lose all the work you’ve done since the last time you saved it.
Hard Drives The primary mass storage device on your computer is the hard drive (also called the hard disc). The hard drive is located inside the system unit and isn’t accessible without opening the box (see Figure 10). Storage devices on your computer are designated by letter, where each drive is assigned its own letter. The hard drive is almost always designated as drive C:. (Note the colon following the ‘C’. Drive letters are always followed by a colon.) It is possible for a computer to have more than one hard drive. There are no standard letter designations for these – they could be assigned any letter from ‘D:’ on up.
Figure 15: Hard drive
The capacity of the hard drive is one factor that influences a computer’s performance. The capacity of hard drives is measured in GB (gigabytes). A typical hard drive in a modern computer will have several hundred GB. Terabyte (TB = 1000GB) drives are now available.
Removable Storage Hard drives are typically mounted inside the system unit, and aren’t easy to remove. When you need portable data storage so that data can be used on more than one machine, moving a typical hard drive isn’t feasible. Portable data storage is also referred to as removable media storage. The most common removable media technologies are optical discs (CDs and DVDs), floppy discs, and flash memory. When referring to disc storage (either optical or floppy), there are two entities to be concerned with: the disc and the drive. The drive is permanently installed on the system unit. The disc is the removable storage medium. The disc is inserted into the drive for reading and writing then removed for travel. The disc can then be inserted into a similar drive on a different computer, making the data available to that machine. The terms drive and disc are often used interchangeably when referring to disc media. There two types of optical disc: the CD (compact disc) and the DVD (digital video disc). You are probably familiar with music CDs and video DVDs. However, these discs can also be used to store computer programs and data. DVDs have a much higher data capacity than CDs do and DVD drives can play video discs on your computer. Video DVDs can’t be played on a CD drive.
Figure 16: CD Drive
There are three types of optical drives based on their ability to write data to the disc. These types apply to DVDs, as well as CDs. CD-ROM – the data is stored on the disc during the manufacturing process and can’t be overwritten. Most software programs are distributed in this format. CD-R – the disc can be written to one time. Once written, it can’t be rewritten. Writing data to an optical disc is often referred to as ‘burning the disc.’ CD-RW – this disc can be written to then rewritten several times. The burning process is relatively slow, so CD-RW drives typically aren’t used to store data that changes often. In order to utilize the write capacity of an optical disc drive, you must also use the right kind of disc. CD-R discs can be burned once using either a CD-R or CD-RW drive. They can’t be rewritten, even with a CD-RW drive. CD-RW discs can be written once using a CD-R drive. If you want to rewrite an optical disc, you must use both a CD-RW disc and a CD-RW drive. An older removable media technology is called a floppy disc. Floppy discs store data magnetically. Compared to other types of removable storage devices, floppy discs were slow, low capacity, and unreliable. As better technologies were developed, floppy discs fell out of favor. Newer computer systems don’t come with floppy drives (they can be special ordered). However, this transition only occurred a few years ago and many computers with floppy drives are still being used today.
Figure 17: Floppy Disc and Drive
PC Peripherals In additional to the various devices found inside the system unit, computers also rely on equipment located outside the box. These external pieces of equipment are known as peripherals. Peripherals can be classified as input devices, output devices, or both. Input devices are those that provide data to the computer. Examples of input devices include the keyboard, mouse, game controller, and camera.
Keyboard
Mouse Game Controller
Web Camera with Microphone
Figure 18: Input Devices
Output devices are those that receive data from the computer. Examples of output devices include the monitor (screen), printer, and speakers.
Monitor
Printer Figure 19: Output Devices
Speakers
Connecting Peripherals Peripheral devices must be connected to the system unit with an electrical cable in order to pass data back and forth. The electrical connector on the system unit where the cable connects is called a port. Some peripherals use specialized ports. For example, the monitor uses a port called the VGA port. However, most peripherals connect to a USB (universal serial bus) port. The system unit will have several USB ports, a few on the front and more on the back.
Figure 20: Ports on the Back
Figure 21: USB Port and Cable
Flash Drives A non-volatile memory technology that has become popular is the last few years is known as flash memory. This is the same type memory used in digital cameras, cell phones, and MP3 players. Portable storage devices that use this technology are called flash drives. Most flash drives are designed to plug into a USB port on your computer (although there are other styles).
Figure 22: USB Flash Drive
For portable data storage, the USB flash drive can’t be beat. It’s fast, high capacity, durable, and inexpensive. The biggest problem with flash drives is losing them. Flash drives go by many different trade names, such as Pin Drives, Key Drives, Jump Drives, Thumb Drives, Memory stick, etc. But they are all based on flash memory technology, so are referred to generically as flash drives. Current flash drives range in capacity from 512MB – 16GB and typically cost between $10 and $50 dollars based on size. Software We previously defined software as, “the instructions that control the hardware in order to implement data processing.” Further, we said that the list of instructions to accomplish a particular task was called programming. These programs are saved on storage devices, such as hard drives, in an electronic format. When we open an application on our computer, such as a web browser or email, the program is copied from the hard drive to RAM for executing. Software can be divided into two broad categories: system software and application software. System software controls the basic operation of the computer, such as reading keystrokes from the keyboard, monitoring the movement of the mouse, outputting video information to the monitor, controlling the hard drive and sending jobs to the printer. Application software allows the user to accomplish a meaningful task, such as playing a game, writing a letter, finding a web page, watching a video, or balancing the checkbook.
System Software The system software running on a particular machine is called ‘the operating system.’ The operating system provides the interface between the user and the computer so the user can tell the computer what they want it to do. There are two basic styles of user interface: the command line interface (CLI) and graphical user interface (GUI, gooey for short). Command line interfaces are difficult to use because commands must be typed on the keyboard. The user must know what commands are available, what they do, and the proper format for entering them. (The proper format for entering a command is known as the command syntax.) When using a command line interface, the user must be highly trained prior to using the computer. Some well-known CLIs are MS-DOS, CP/M, UNIX, and the Windows command prompt.
Figure 23: The Windows Command Prompt
With a graphical user interface (GUI) the user communicates with the computer using a pointing device (such as a mouse). Using the mouse, the user points to an icon (a screen graphic that represents an application or command) on the screen and clicks the mouse button. Using a GUI interface, a user can begin accomplishing useful tasks on the computer after just a short tutorial on how to use the mouse. GUI operating systems are the standard today. The most popular are Windows and Macintosh.
Figure 24: Windows GUI
Application Software Application software is sometimes referred to as ‘productivity’ software. Applications are run by the operating system to allow users to accomplish meaningful tasks. Examples of typical applications would include word processors to assist the user in creating written documents, spreadsheets to help the user with repetitious calculations, presentation software to help the user create attractive slide presentations, web browsers to surf the Internet, games for recreation, and many more. Most operating systems come with some basic applications included. More sophisticated software must be purchased separately. For example, Microsoft Windows comes with a basic word processor called WordPad (Figure 25), a basic drawing program called Paint, a web browser called Internet Explorer (Figure 26), a calculator, several games (Figure 27), and more. However, the most popular business software, Microsoft Office, does not come with Windows.
Figure 25: WordPad
Figure 26: Internet Explorer
Figure 27: Solitaire
Data We previously defined data as, “the facts and figures that are processed by the software and hardware to produce a useful output.” For example, if we write a letter using a word processor application, the letter is the data we created. If you create a drawing in Paint, the drawing is the data. If you save a game so you can finish it later, the saved game is the data. After creation, data must be saved to a storage medium (hard drive, flash drive, etc.) to be used later. Always remember to save your data after creating it. If you close the application without saving, the data will be lost and is unrecoverable. Applications designed for use with the Windows operating system will warn you if you attempt to close the application without first saving your data.
Figure 28: Windows Save As Box
The data created using a particular application is only good for that application. For example, you write a letter using a word processor application. You save the letter then send it to a friend using email. The friend may not be able to open the letter if they don’t have the same word processor software you used. Most applications allow you to save your data in a generic format that will be compatible with similar applications, but you must remember to use this generic format. There will be more discussion on this subject later in the course. Turning it On To turn on your computer, look for a button with this symbol (this is the standard power button symbol) on the front of the system unit. Press and release it.
Figure 29: Power Button Symbol
You must also turn on the monitor. A common mistake on desktop computers is turning on either the system unit or the monitor, but not the other. This is an easy mistake to make, especially if the system unit is sitting on the floor. If you think the computer should be on, but the screen stays black, check to be sure that both the system unit and the monitor have been turned on. (This is only a concern with desktop models; laptops only have one power button.) You may recall that early in this discussion you were introduced to ROM memory. Not much was said about it at the time and you may have wondered about its significance. Well, the waiting is over. When you first turn on the system unit, RAM is empty because it is volatile (do you remember what that means?). If RAM were the only memory, the CPU wouldn’t be able to get the operating system off the hard drive. However, there is another section of memory called ROM. ROM can’t be easily written to, but it is non-volatile. ROM holds the basic instructions needed to get the computer started and the operating system loaded into RAM. The first instructions in ROM cause the CPU to execute a power-on self test (POST). POST checks RAM and several other critical subsystems, such as the keyboard, to be sure they are functional. Once the POST is complete and all the systems have checked out, the operating system is copied from the hard drive into RAM. At this point control of the computer is turned over to the operating system and we’re off and running. Boot Up The process just described to get the computer up and running is called boot up. There are two types of boot up: cold boot and warm boot. A cold boot occurs when the computer has been powered down and is turned back on using the power button. A cold boot includes the POST. A warm boot occurs when the system must do a restart after installing some types of software. In this case the reboot is initiated by the computer, not the power button (you can instruct Windows to execute a warm boot by using the Restart utility). A warm boot does not include the POST, but other than that, a warm boot and cold boot are the same.
Turning It Off Many people leave their computers running all the time. There is nothing wrong with that. But other people like to shut their computer off when not in use. DON’T turn off your system unit the same way you turned it on. The operating system needs to shut down the systems in an orderly fashion. The proper way to turn off your system unit is to implement the Shutdown utility in the operating system. It is okay to use the power button on your monitor.
Restart (warm boot) Shutdown
Figure 30: Windows Shutdown
One last tip. There is one situation when you will need the power button to turn off your system unit. If the operating system freezes up and will not respond to the keyboard or mouse, press and hold the power button for several seconds (pressing and releasing the power button won’t do it). The computer will power down. Wait a few seconds then press the power button again to turn the unit back on. Only use this procedure as a last resort. The operating system doesn’t like it and will run several diagnostic routines to be sure everything is alright before loading the operating system on the next boot up. Good luck and good computing!
