learnings of thew week

this week, i have learned about:
>what is computer?
>what are the types of computers?
>what are the parts of the computer?


>A computer is a machine that manipulates data according to a list of instructions. the first devices that resemble modern computers date to the mid-20th century (around 1940 - 1945), although the computer concept and various machines similar to computers existed earlier. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers.^[1] Modern computers are based on tiny integrated circuits and are millions to billions of times more capable while occupying a fraction of the space.^[2] Today, simple computers may be made small enough to fit into a wristwatch and be powered from a watch battery. Personal computers, in various forms, are icons of the Information Age and are what most people think of as "a computer"; however, the most common form of computer in use today is the embedded computer. Embedded computers are small, simple devices that are used to control other devices — for example, they may be found in machines ranging from fighter aircraft to industrial robots, digital cameras, and children's toys.

The ability to store and execute lists of instructions called programs makes computers extremely versatile and distinguishes them from calculators. The Church–Turing thesis is a mathematical statement of this versatility: any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, computers with capability and complexity ranging from that of a personal digital assistant to a supercomputer are all able to perform the same computational tasks given enough time and storage capacity.

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• PC - The personal computer (PC) defines a computer designed for general use by a single person. While a Mac is a PC, most people relate the term with systems that run the Windows operating system. PCs were first known as microcomputers because they were a complete computer but built on a smaller scale than the huge systems in use by most businesses.

• Desktop - A PC that is not designed for portability. The expectation with desktop systems are that you will set the computer up in a permanent location. Most desktops offer more power, storage and versatility for less cost than their portable brethren.

• Laptop - Also called notebooks, laptops are portable computers that integrate the display, keyboard, a pointing device or trackball, processor, memory and hard drive all in a battery-operated package slightly larger than an average hardcover book.

• Palmtop - More commonly known as Personal Digital Assistants (PDAs), palmtops are tightly integrated computers that often use flash memory instead of a hard drive for storage. These computers usually do not have keyboards but rely on touchscreen technology for user input. Palmtops are typically smaller than a paperback novel, very lightweight with a reasonable battery life. A slightly larger and heavier version of the palmtop is the handheld computer.

• Workstation - A desktop computer that has a more powerful processor, additional memory and enhanced capabilities for performing a special group of task, such as 3D Graphics or game development.

• Server - A computer that has been optimized to provide services to other computers over a network. Servers usually have powerful processors, lots of memory and large hard drives.

• Mainframe - In the early days of computing, mainframes were huge computers that could fill an entire room or even a whole floor! As the size of computers has diminished while the power has increased, the term mainframe has fallen out of use in favor of enterprise server. You'll still hear the term used, particularly in large companies to describe the huge machines processing millions of transactions every day.

• Minicomputer - Another term rarely used anymore, minicomputers fall in between microcomputers (PCs) and mainframes (enterprise servers). Minicomputers are normally referred to as mid-range servers now.

• Supercomputer - This type of computer usually costs hundreds of thousands or even millions of dollars. Although some supercomputers are single computer systems, most are comprised of multiple high performance computers working in parallel as a single system. The best known supercomputers are built by Cray Supercomputers.

• Wearable - The latest trend in computing is wearable computers. Essentially, common computer applications (e-mail, database, multimedia, calendar/scheduler) are integrated into watches, cell phones, visors and even clothing!

>s we learned in the Overview portion of the study guide, a computer system has two basic parts: hardware and software. The equipment associated with a computer system is the hardware. Computer hardware is responsible for performing four basic functions: input, processing, output, and storage. Let’s go back to the basic definition of a computer. A computer is an electronic device that is programmed to accept data (input), process it into useful information (output), and store it for future use (storage). The processing function is under the control of a set of instructions (software); we will explore this later.

The four primary components of a computer system are:

Input	Input devices send data and instructions to the central processing unit.
Output	Central processing unit executes computer instructions. Memory holds data and programs temporarily.
Processing	Output devices make processed data available to the user.
Secondary Storage	Secondary storage devices store data and programs permanently.

In order to function properly, a computer system must have all four types of hardware: input, processing, output, and storage.

In this example, the mouse and keyboard are the input devices and the monitor and speakers are output devices. The processor is contained inside the tower unit and the storage devices are the hard drive, CD-ROM drive and the diskette drive. Let’s explore each of the devices in detail.

Input devices accept data in a form that the computer can utilize. Also, the input devices send the data or instructions to the processing unit to be processed into useful information. There are many examples of input devices, but the most commonly used input devices are shown below:

The input device feeds data, raw unprocessed facts, to the processing unit. The role of the processing unit or central processing unit is to use a stored program to manipulate the input data into the information required. In looking at the computer system below, the Central Processing Unit, CPU, is not exactly visible. The CPU is found inside the tall, vertical unit, called a tower, located just to the right of the monitor.

The CPU is the brain of the computer. The CPU consists of electronic circuits that interpret and execute instructions; it communicates with the input, output, and storage devices. The CPU, with the help of memory, executes instructions in the repetition of machine cycles. A machine cycle consists of four steps:

1. The control unit fetches an instruction and data associated with it from memory.
2. The control unit decodes the instruction.
3. The arithmetic/logic unit executes the instruction.
4. The arithmetic/logic unit stores the result in memory.

The first two instructions are called instruction time, I-time. Steps 3 and 4 are called execution time, E-time. The speed of computer is measured in megahertz, MHz.

A MHz is a million machine cycles per second. A personal computer listed at 500 MHz has a processor capable of handling 500 million machine cycles per second. Another measure of speed is gigahertz (GHZ), a billion machine cycles per second. A third measure of speed is a megaflop, which stands for one million floating-point operations per second. It measures the ability of the computer to perform complex mathematical operations.

Memory, or primary storage, works with the CPU to hold instructions and data in order to be processed. Memory keeps the instructions and data for whatever programs you happen to be using at the moment. Memory is the first place data and instructions are placed after being input; processed information is placed in memory to be returned to an output device. It is very important to know that memory can hold data only temporarily because it requires a continuous flow of electrical current. If current is interrupted, data is lost. Memory is in the form of a semiconductor or silicon chip and is contained inside the computer.

There are two types of memory: ROM and RAM. ROM is read only memory. It contains programs and data that are permanently recorded when the computer is manufactured. It is read and used by the processor, but cannot be altered by the user. RAM is random access memory. The user can access data in RAM memory randomly. RAM can be erased or written over at will by the computer program or the computer user. The amount of RAM has increased dramatically in recent years.

Memory is measured in bytes. A byte is usually made up of 8 bits and represents one character—a letter, digit, or symbol. The number of bytes that can be held is a measure of the memory and storage capacity. Bytes are usually measured in groups of kilobytes, megabytes, gigabytes, and terabytes. The following chart defines each term.

Kilobyte	KB	Roughly 1,000 bytes
Megabyte	MB	Roughly 1,000,000 bytes
Gigabyte	GB	Roughly 1,000,000,000 bytes
Terabyte	TB	Roughly 1,000,000,000 bytes

Memory is usually measured in Megabytes; a typical personal computer will have 64MB or more. Storage is usually measured in Gigabytes.

Since we have said that memory is in the form of chips and must maintain a constant flow of electricity, there must be a more permanent form of storage that does not depend on a constant flow of electricity. That form of storage is called secondary or auxiliary storage. The benefits of secondary storage are large space capacity, reliability, convenience and economy.

Magnetic disk storage is a very popular type of secondary storage—the floppy disk drive is an external disk drive, while a hard disk drive is an internal disk drive. The floppy disk drive is usually a 3 ½" drive and uses a diskette made of flexible mylar and coated with iron oxide, a substance that can be magnetized. A diskette records data as magnetized spots on the tracks of its surface. A floppy disk can hold 1.44 MBs, or a ‘Zip’ drive can hold 100 MBs.

A hard disk, an internal disk, is a metal platter coated with magnetic oxide that can be magnetized to represent data. Hard disks come in a variety of sizes and can be assembled into a disk pack. Hard disks for personal computers are 3 ½" disks in sealed modules. A hard disk is capable of holding a great deal more than floppy disks. Hard disks for personal computers are measured in gigabytes. (Remember, a gigabyte is roughly a thousand megabytes or a thousand floppy disks.)

While the size or data capacity of a hard drive is very important, the speed of accessing that data is equally as important. Files on hard drives can be accessed significantly faster and more conveniently than floppy drives.

Hard Drive

The ever-demanding need for storage has required even better storage capacity than that of magnetic disks. Optical disk technology meets that need. Included in the list of this type of technology is the optical disk, the CD-ROM or DVD-ROM. The CD-ROM, compact disk read-only memory can hold up to 660 MBs per disk or the equivalent of more than 400 standard 3 ½" diskettes. The new storage technology that outpaces all others is called DVD-ROM, digital versatile disk. The DVD has a 4.7 GB capacity, which is about seven times that of the CD-ROM.

In order to protect the data on your hard drive, you should have a backup system. A backup system is way of storing data in more than one location. Magnetic tape is usually used for this purpose. Magnetic tape is an inexpensive type of storage; it looks like the tape used in audiocassettes.

Finally, the last component of a computer system is the output device. An output device displays the processed information to the user. The two most popular forms of output devices are the printer and the monitor. The monitor produces output that is temporary—the output is lost when it is rewritten or erased or when power is lost. Monitor output is called softcopy. The printer displays output in a permanent manner; it is called hardcopy. Other types of output devices include voice output and music output devices.