The letters IPOS stand for input, process, output and storage. The IPOS cycle describes to the steps we go through each time we sit down at a personal computer. The words input, process, output and storage are used as verbs as well as nouns. As verbs, IPOS refers to actions we take while using a computer. As nouns, IPOS refers to computer components or categories of computer hardware we use to perform the actions of inputting, processing, outputting and storing data/information on a computer.
Input: We enter data into the computer with a device such as a keyboard or a mouse.Process: The central processing unit (CPU), along with random access memory (RAM), changes the data into information.
Output: The results of the processing by the CPU are given back to the operator, usually either displayed on the computer screen or sent to the printer.
Storage: The results of processing are saved for later use on a storage device such as a floppy or hard drive.
Everything stored on a computer, no matter how large or small the computer may be, is represented as a series of ones and zeroes arranged in unique patterns. Whether it is the data we enter with a keyboard or microphone or the programs we use to accomplish tasks such as sending email or adding a column of numbers, everything stored on a computer is represented as a series of ones and zeroes.
A binary digit is either a one or a zero, the two numbers in a binary numbering system. Computers use binary digits as the building blocks of the programs and data stored on a computer. Just as bricks can be arranged in patterns to form patios, barbecues or walls, binary digits can be arranged in patterns to represent programs and data stored in a computer. The term bit is often used to refer to the ones and zeroes used by computers. The term bit is a contraction of the two words binary and digit.
There are two meanings for the term byte.
The terms kilobyte, megabyte, gigabyte and terabyte refer to a collection of bytes stored in a computer. There are 1024 bytes in kilobyte, 1024 kilobytes in a megabyte, 1024 megabytes in a gigabyte and 1024 gigabytes in a terabyte. Although the above definitions are the accurate definitions, the terms kilobyte, megabyte, gigabyte and terabyte also have a popular definition. A kilobyte is popularly referred to as 1000 bytes, a megabyte is popularly referred to as a million bytes, a gigabyte as billion bytes and a terabyte as a trillion.
There are four types of data, numeric (numbers), textual (words), audio/visual, (sounds or pictures) and physical (measurements such as temperature or weight).
While the terms data and information are often used synonymously in everyday conversation, with regard to computers, there is an important distinction between the two. Data are raw facts that have little value in and of themselves. Information is something we can use. One way to think of a computer is as a system for producing information. We enter data (raw facts) into the computer and the CPU, along with RAM, take that data and transform it into information. Together, the CPU and RAM are often referred to as the system unit.
Input hardware is used to enter data into a computer; output hardware is used to display or relay the results of a computer's processing. Examples of input hardware are a keyboard, a mouse, microphone, a hard drive or a modem. Examples of output hardware are a computer screen, speakers, a hard drive, a modem or a printer. As you can see, some devices can serve as both input and output devices.
The role of storage is to retain the results of processing for future use. As a computer changes data into information, the results of processing are only held temporarily in memory. In this context, temporary means only as long as the computer has a sufficient and constant supply of electricity. If a computer loses power for any reason, even for a tiny fraction of a second, memory disappears and the results of processing are lost. Once we save information to devices such as disk drives (hard, zip or floppy), tape drives, a CD or DVD, we can retain the results of processing (information) even after the computer is turned off or loses power.
Storage and memory both hold data and program instructions. They differ in how they do this. Two differences between storage and memory are:
Storage is long term, it doesn't need electricity to retain its contents; memory is temporary (volatile), it needs a constant supply of electricity or memory and all its contents disappear. Data or program instructions needed by a computer can be found in one of two places, memory or storage. The amount of time it takes a computer to receive data or program instructions is called access time. The access time of memory is measured in nanoseconds or billionths of a second. Access time for storage devices is measured in milliseconds or thousandths of a second. In other words, if a computer can find what it needs in memory, it will get it in 40-80 nanoseconds. By contrast, if a computer must get the data or program instructions it needs from a hard drive, it will take 10-15 milliseconds.
Two lesser differences between storage and memory are:
A computer typically has much more storage capacity than memory capacity (gigabytes vs. megabytes). A typical computer today will have 60-120 gigabytes of storage capacity on its hard drive. The same computer will have 128-512 megabytes of memory. Storage is less expensive than memory.
Although the term computer commonly refers to the combination of system case (box), keyboard, mouse and monitor, in actuality the computer is only one chip in the case. This chip is known as the central processing unit or CPU for short. A CPU is composed of two different parts, the Arithmetic Logic Unit (ALU) and the Control Unit. For all the varied tasks that a computer can perform, the only tasks it is actually capable of are math, logic and control. By math we mean the CPU has the ability to add numbers. Logic refers to the CPU's ability to compare one quantity to another. Math and logic are carried out by the Arithmetic Logic Unit. By control, we mean the CPU's ability to move data into memory or to request that data or instructions be sent from memory to the CPU for processing. Control is handled by the Control Unit.
Inside every computer is a crystal that vibrates a fixed number of times per second. This crystal drives the computer's system clock. The system clock doesn't keep the time of day. Instead, the system clock is a timing device used to coordinate system events. Much like a band uses the beat of a drum to keep time, a computer turns transistors on and off to the beat of the system clock. With every tick of the clock, a transistor is turned on, a 1, or off, a 0. With every tick of the clock, a computer completes a cycle. The faster the clock ticks (the crystal vibrates), the faster a computer can process data. The term Megahertz means millions of cycles. Megahertz is a measure of how many millions of cycles per second a computer can complete. The higher the Megahertz rating, the faster and more powerful the computer is.
In addition to the system clock, computers have another clock called the real time clock. This clock is battery operated and keeps track of the date and time. Don't confuse the system clock with the real time clock.
Every CPU is designed to understand a limited number of instructions. The number of instructions a CPU understands is called its instruction set. One way to classify CPUs is by the number of instructions it understands, a complex set (CISC) or a reduced set (RISC). CISC chips understand a larger number of instructions than RISC chips. The ability to understand a larger set of instructions might seem like an advantage but it isn't. A RISC chip's instructions are smaller and simpler than those of a CISC chip. Because of this, generally speaking, a RISC chip will perform faster than a CISC chip operating at the same Megahertz. In addition to being faster, RISC chips are also less expensive to build.
Symmetric multiprocessing, also referred to as parallel processing, is the use of more than one CPU in a computer. The use of two or even four CPUs in a personal computer is not uncommon today. Although using more than one CPU does make a computer faster, a computer with two CPUs won't be twice as fast as a computer with one CPU. Also, just because a computer has more than one CPU doesn't mean its software can use more than one CPU at time. It is much more difficult to write programs that can take advantage of multiple CPUs so there is not nearly as much multiprocessor-ware software available.
Memory, also called Random Access Memory (RAM), is a CPU's temporary workspace. A CPU uses this workspace to hold program instructions, data and the results of processing. Without memory, a CPU would have no place to store data and program instructions. Program instructions and data are held in memory until the CPU needs them and the results of processing are then placed in memory once the computer finishes a task.
Memory's two most prominent features are its speed and volatility.
Speed: When data or program instructions are held in memory, they can be accessed in nanoseconds or billionths of a second. An access time of 60-80 nanoseconds is common.Volatility: Memory must have a constant flow of electricity at a certain level in order for it to hold data or instructions. If power should be cut off momentarily or even dip below a certain level, memory and all its contents disappear.
RAM is described as volatile because it disappears if the computer doesn't have a constant and sufficient supply of electricity. Even if electricity is still available but dips below the computer's required level, that would be enough for RAM and all its contents to disappear.
One measure of a computer's power is throughput. Throughput is a measure of the amount of time it takes a computer to complete a task. The single most important factor that determines the power of a computer is the speed of its CPU. However, the amount of RAM installed in a computer plays a major role in how powerful a computer is. RAM affects a computer's power in three ways.
The fastest component of a computer system is usually the CPU. The CPU is so much faster than some of the other components such as the hard drive that it often sits idle waiting for something to do. The term cache refers to a temporary storage location for data. The purpose of a cache is to provide a CPU with the data it needs as quickly as possible. A cache does this by anticipating what data a CPU will need next and by placing needed data where the CPU can most quickly find it. The two main types are disk and memory caches. A disk cache uses regular RAM while a memory cache uses a small amount of high speed RAM. Since a cache reduces the amount of time the CPU sits idle, the result is an increase in system throughput.
To boot a computer means to turn it on and have it go through the steps necessary for it to be able to accept and follow commands from an operator. When a computer is first turned on, control of the system is taken over by a chip on the computer's motherboard called ROM. ROM stands for Read Only Memory. ROM contains instructions that tell the rest of the computer system how to proceed with the boot process. Before a computer is ready to accept commands, it has to determine what components are connected to the system and to verify that all components are working properly. Once this is accomplished, control of the computer is turned over to the operating system.
Another name given to the ROM chip is BIOS. BIOS stands for Basic Input/Output System. ROM and BIOS are two different names for the same chip.
Unlike the contents of RAM, the instructions found in ROM (Read Only Memory) are wired into the chip and so don't disappear when the computer is turned off. Also unlike RAM, the instructions held in ROM can't be changed easily or at all. Although some newer computers have the ability to let you use software to change the instructions found in ROM, for many computers, if you need a different set of ROM instructions, you must remove the chip and put in a new one. When a computer is first turned on, instructions found in ROM tell the computer how to proceed with the process of getting the computer ready to accept instructions from the user. By contrast, RAM only exists as long as the computer has electricity.
A motherboard is a piece of fiber glass containing the electrical circuitry that links the various computer components found inside the computer's case. Some of the components you'll find on a motherboard include the CPU, memory, the ROM chip or BIOS, the computer's power supply, the expansion bus and expansion cards.
A computer bus is a collection of circuits that carry electricity to and from the system components. Although computers have several different buses, the two main types of buses a computer has are data and address buses. A data bus carries data from system components to the CPU and back again. An address bus carries the address in memory where the CPU will find the data or program instructions needed for processing. Some examples of buses are ISA (Industry Standard Architecture), PCI (Peripheral Component Interconnect), USB (Universal Serial Bus) and SCSI (Small Computer System Interface).
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