In a spreadsheet, a cell range is defined by the reference of the upper left cell (minimum value) of the range and the reference of the lower right cell (maximum value) of the range. Eventually separate cells can be added to this selection, then the range is called an irregular cell range. In Excel, the minimum and maximum value are included.

Analog computer that performs arithmetical operation by measurable quantities, such as mechanical movement, the rotation of gears rather than by number. In Analog computers, data is transmitted for its operation in the form of continuous signals, while in digital computers in the form discrete signals (or discontinuous signal).

Examples of analog computer are temperature, pressure, telephone lines, Speedometer, resistance of capacitor, frequency of signal and voltage etc.

Digital Computers. Digital computer represents physical quantities with the help of digits or numbers. These numbers are used to perform Arithmetic calculations and also make logical decision to reach a conclusion, depending on, the data they receive from the user.

The characteristics of computers that have made them so powerful and universally useful are speed, accuracy, diligence, versatility and storage capacity. Let us discuss them briefly.

• Speed: Computers work at an incredible speed. A powerful computer is capable of performing about 3-4 million simple instructions per second.
• Accuracy: In addition to being fast, computers are also accurate. Errors that may occur can almost always be attributed to human error (inaccurate data, poorly designed system or faulty instructions/programs written by the programmer)
• Diligence: Unlike human beings, computers are highly consistent. They do not suffer from human traits of boredom and tiredness resulting in lack of concentration. Computers, therefore, are better than human beings in performing voluminous and repetitive jobs.
• Versatility: Computers are versatile machines and are capable of performing any task as long as it can be broken down into a series of logical steps. The presence of computers can be seen in almost every sphere – Railway/Air reservation, Banks, Hotels, Weather forecasting and many more.
• Storage Capacity: Today’s computers can store large volumes of data. A piece of information once recorded (or stored) in the computer, can never be forgotten and can be retrieved almost instantaneously.

Computer systems consist of three components as shown in below image: Central Processing Unit, Input devices and Output devices. Input devices provide data input to processor, which processes data and generates useful information that's displayed to the user through output devices. This is stored in computer's memory. There are five main hardware components in a computer system: Input, Processing, Storage, Output and Communication devices.

Hardware is the tangible components of the computer system which can be used to give input, store data and showing results. The popular hardwares are mouse, keyboard, monitor, printer, processor, motherboard, cables, etc.

Software is a program or set of instructions used to do a specific task. The software cannot be seen by users. Users can realize and validate their functions only. All the softwares run on the hardware.

The most popular software in the computer system is Operation System (Windows, Linux, Ubuntu, etc.), Microsoft Office (MS Word, Excel, PowerPoint, etc.)

Software is a set of instructions, data or programs used to operate computers and execute specific tasks. Software is often divided into categories. Application software refers to user-downloaded programs that fulfill a want or need. Examples of applications include office suites, database programs, web browsers, word processors, software development tools, image editors and communication platforms.

Characteristics of a computer system let us know about its capabilities. The followings are the key characteristics of the computer system.
 

1. Speed: The computer is a much faster device. A computer machine can solve very complex problems faster than a person. It gives results within a second. Now a day, the computer can solve not only a single problem but also multiple problems within very less time.
2. Data Storage: A computer system can store a large amount of data for a long time period. The data can be store in internal as well as external devices. The internal device of data storage is Hard disk and external storage devices are Pen drive, External Hard disk, etc.
3. Accuracy: Computers can generate reliable results with high computational speed. If the input is right then only the appropriate output will be generated. The computer never gives inaccurate results; if results are inaccurate it means inputted data was erroneous.
4. Versatility: A computer is a versatile machine that can perform different types of jobs with the same accuracy rate.
5. Diligence: Computers never get tired. As humans get tires when he works regularly but the computer can perform tasks over and over again, with the same outcome, and it does so without tiring.
6. No IQ: It performs a task that is exactly as directed by the user because it does not have its intelligence.
   Reliable: Consistency refers that a computer is a reliable machine, as it always gives consistent results.

Control Unit controls all the devices connected to the computer system so that interrupt or unavoidable circumstances between device communications cannot happen. CU not only controls device communication but also program executions. CU mainly communicates between processor, memory and computer peripherals (input/output devices).

ALU stands for the Arithmetic and Logical Unit. This is an important element of the computer system which is used to perform arithmetic and logical operations. ALU is a part of a computer processor.

• Primary memory is also called internal memory whereas Secondary memory is also known as a Backup memory or Auxiliary memory.
• Primary memory can be accessed by the data bus whereas Secondary memory is accessed by I/O channels.
• Primary memory data is directly accessed by the processing unit whereas Secondary memory data cannot be accessed directly by the processor.
• Primary memory is costlier than secondary memory whereas Secondary memory is cheaper compared to primary memory.
• Primary memory is both volatile & nonvolatile whereas Secondary memory is always a non-volatile memory.

Popular output devices are printer, monitor, and plotter etc. Monitor displays the character and graphic on screen. There are CRT and LCD monitors. Printer is used to print the result on the paper.

Keyboard – one of the primary input devices used to input data and commands. 
Mouse – an input device used to control the cursor and coordinates. It can be wired or wireless.
Microphone – an input device that allows users to input audio into their computers.
Digital Camera – is an input device that takes pictures digitally. 
Scanner – is an input device that reads an image and converts it into a digital file.
Touchscreen – is an input device that allows users to interact with a computer using their fingers.

The major elements of the computer system are as follows –

1. Memory
2. ALU
3. Control Unit
4. Hardware and Software

1. Memory

Memory is also known as the storage medium of the computer system. This is a storage device that can store data/information. Memory is primarily categorized into two parts,

1. Primary Memory:
   This is also known as the main memory or temporary memory or volatile memory. This memory device stores data for a temporary period. Programs or instructions execute in Primary Memory.
   Primary Memory further categorized into two parts –
   1. RAM (Random Access Memory)
   2. ROM (Read Only Memory)
2. Secondary Memory:
   Secondary memory is a memory that can store a large amount of data in it. Once, data is saved into secondary memory cannot delete until and unless the user's permission. It is also known as a permanent memory.

2. ALU

ALU stands for the Arithmetic and Logical Unit. This is an important element of the computer system which is used to perform arithmetic and logical operations. ALU is a part of a computer processor.

3. Control Unit

Control Unit controls all the devices connected to the computer system so that interrupt or unavoidable circumstances between device communications cannot happen. CU not only controls device communication but also program executions. CU mainly communicates between processor, memory and computer peripherals (input/output devices).

4. Hardware and Software

Hardware is the tangible components of the computer system which can be used to give input, store data and showing results. The popular hardwares are mouse, keyboard, monitor, printer, processor, motherboard, cables, etc.