Computer System Overview Class 11 CS | Unit – 1 Sumita Arora

Computer Organization	Input Unit	Output Unit
CPU	Memory	Storage
System Bus	Mobile System	Operating System
Language Processors	Application Software	Software Libraries

What is a computer?

A computer is an electronic device that can be programmed to accpect input data, process the data according to the user’s need and export the result that would be output.

Basic computer Organization

Computer organization refers to the logical structure of a computer describing how its components are connected: how they effect one another’s functioning and contribute to the overall performance of the computer.

So, the computer organization is also like this these are component (s) dedicated to obtaining input in diferent forms, component(s)dedicated to performing processing parts and component(s) to produce output in different forms.

Input Unit

Since a computer operates on electricity, it can understand only the language of electricity i.e., either ON or OFF or high voltage or low voltage. That means a computer can understand two stages ON/OFF or High/Low voltage or the binary language that uses just two symbols: 1 for ON and 0 for OFF.

Computer input also consists of data and instructions,

The input unit is consist of different input devices that take the input in different forms and pass them in digital form to CPU for processing.

Some common input devices are:

1. Keyboard: A keyboard is a typewriter-like device that is used to type in letters, digits and commands.
2. Mouse: The mouse is a pointing device with either a roller on its base or some laser mechanism. Mouse controls the movement of pointer (also called the mouse pointer) on the screen.
3. Microphone(Mic): We can send sound input to a computer through a special input device called a microphone or mic in short. A mic converts the sound received into a computer’s format, which is called digitized sound or digital audio. A mic can work if your computer has a special hardware known as a sound card.

Output Unit

Some common output devices are:

1. Monitor: It displays information. The pictures on a monitor are made up of thousands of pixels.
2. Printers: Printers are the devices that deliver information using printed characters on paper.
3. Speakers: Speakers receive sound in the form of electric current from the sound card and convert it into an audible format for users.

CPU Unit – Central Processing Unit

The CPU is parted into 3 parts that is:

1. ALU: Arithmetic Logic Unit
2. CU: Control Unit
3. Registers

ALU – Arithmetic Logic Unit

Arithmetic

• When two numbers are added, these are sent to the ALU from the memory.
• The addition takes place then the result is put back in the memory.

Logical

• Sent to the memory to ALU where the comparison takes place
• And returned to memory

CU – Control Unit

The CU sends control signals until required operations are done by ALU and memory. The CU controls and guides the interpretation, flow and manipulation of all data and information.

• CU acts as a supervisor by controlling and guiding the operation taking place
• Another important function of CU is the program execution i.e., carrying out all the instructions stored in the program. The CU gets program instructions from memory and executes them one after the other. After getting the instructions from memory in CU, the instruction is decoded and interpreted i.e., which operation is to be performed.
• Then the asked operation is carried out. After the work of this instruction is completed, control unit sends signal to memory to send the next instruction in sequence to CU.
• The control unit even controls the flow of data from input devices to memory and from memory to output devices.

Registers

• Registers or processor registers are small units of data holding places.

• The CPU uses registers to temporarily hold some important processing information during the time the processing is taking place.

• CPU may store some part data or some memory address or some instruction in its processor registers.

Memory (Main/Primary)

The memory of a computer is more like a predefined working place, where it temporarily keeps information. Each memory location has a unique memory address.

When the task is performed, it clears its memory and memory space is then available for the next task to be performed.

• The memory of a computer can be thought of as ‘cells’. Each of these cells is further broken down into smaller parts known as bits.
• A bit means a binary digit i.e., either 0 or 1. Several bits together are used to store data instructions by their combination.

• A bit is an elementary unit of memory. Eight bits together form a byte.

• One byte is the smallest unit which can represent a data item or a character.

• Other units of memory are KB, MB, GB, TB.

• Every higher memory unit is equal to 2 of it’s lower unit.

Some most common secondary storage media are hard disk, CD-RW’s, pen drives &b etc. The secondary memory devices are also known as storage devices.

RAM – Random Access Memory

RAM allows information transfer from any random location, but its main drawback is that it loses all data when power is lost due to its volatile nature.

RAM in a computer can be of two types:

1. Dynamic RAM (DRAM): These are made of transistors and capacitors. Today’s DRAM Chips have access times below 20-70 nanoseconds.
2. Static RAM (DRAM): These are made up of flipflops and offer faster access times (about 10 nanoseconds) than DRAMS, thus are utilized in specialized applications.

ROM– Read Only Memory

• A Read-Only Memory (ROM) is a memory unit that performs the read operation only; it does not have a write capability. This implies that the binary information stored in a ROM is made permanent during the hardware production of the unit and cannot be altered by writing different words into it (hence non-volatile).
• Whereas RAM is a general-purpose device whose contents can be altered during the computational process, a ROM is restricted to reading words that are permanently stored within the unit.
• ROMs are used for applications in which it is known that the information never needs to be altered. Example: a monitor program controlling a machine. These, however, are slower than RAM.

There are many types of ROM, but we will only cover that’s in our syllabus:

1. PROM (Programmable ROM): Also called OTP (One Time Programmable). PROM is a user-programmable memory in which information is burnt using special equipment called a ROM burner.
2. EPROM (Erasable Programmable ROM): In EPROM, one can program the memory chip (through various mechanisms e.g., UV radiation) and erase it many times as needed. The UV-EPROM can take up to 20 minutes to erase EPROM contents.
3. EEPROM (Electrically Erasable Programmable ROM): In EEPROM, the EPROM is erased electrically which is faster. Also, with EEPROM, selective bytes can be erased, unlike UV-EPROM which erases fully.
4. Flash EEPROM: It is like EEPROM but is very fast comparatively (the erasure of the entire contents takes less than a second). Also, it erases fully and not selectively.
5. Mask ROM: Mask ROM is a kind of ROM in which the IC manufacturer programs the contents. It is not a user-programmable ROM.

Storage Unit

Since primary memory has a limited storage capacity and is not permanent, secondary storage devices are used to store large amount of data permanently.

There are various types of secondary devices available these days. To specify the storage capacity of storage devices, same units of memory are used, which are used for measuring primary memory. That is, we can represent the storage capacity of storage devices in terms of kilo bytes (KB‘s), mega bytes (MB‘s), giga bytes (GB‘s) and tera bytes (TB‘s) as we do for main memory.

Some common storage units are:

1. Hard Disks: The hard disk memories store information on one or more circular platters (or disks) which are continually spinning.
   • These rotating disks are coated with a magnetic material and stacked with space between them. Information is recorded on the surface of rotating disks by magnetic heads as tiny magnetic spots. The hard disks of today have storage capacity measured in giga bytes upto tera bytes.
2. Compact Disks: (CDs) The compact disks or CDs are optical media. The CDs are relatively cheap and have a storage capacity of upto 700 Mb. There are three main types of CDs:
   • (i) CD-ROM (Compact Disk-Read Only Memory): This is used only to store information and cannot be used to store data. It is mainly used for CD distribution e.g., encyclopedias, software, games, e-books etc.
   • (ii) CD-R (Compact Disk-Recordable): It is mainly used for CD-R and can be written on only once and disk can’t be erased.
   • (iii) CD-RW (Compact Disk-Rewritable): CD-RW is an erasable disk you can write on multiple times.
3. DVDs: DVD is an optical storage device that looks the same as a compact disc but is able to hold about 15 times as much information and transfer it to the computer about 20 times as fast as a CD-ROM. A DVD, also called a Super Density disk (SD), can hold upto 17 gigabytes of data or four hours of movies on a side. DVDs also come in three varieties.
   • (i) DVD-ROM: This is read only DVDs i.e., once recorded initially, you cannot write on it.
   • (ii) DVD-R (DVD-Recordable): DVD-R similar to CD-R’s allow users to write on the disc once but read it many times.
   • (iii) DVD-RW (DVD-Rewritable): Most writable DVD drives are DVD-RW You can erase and read many times on them.
4. Flash Memory: A flash drive is a small, ultra-portable storage device with a ‘solid state‘ memory i.e., it has no moving parts unlike magnetic storage devices, nor does it make use of lasers – unlike optical drives.
   • Instead, it works in a similar way to RAM. The key difference is that data is retained in Flash memory even when the power is switched off. They are now fairly inexpensive, costing from 250/- upwards. Typical sizes range from 256 Mbytes up to 128 GB and beyond.
5. Blu-Ray:Disk Blu-ray Disc (also known as Blu-ray or BD) is an optical disc storage media format. Its main uses are high-definition video and data storage.
   • The disc has the same dimensions as a standard DVD or CD.
   • The benefit of using a blue-violet laser (405 nm) is that it has a shorter wavelength than a red laser (650 nm), which makes it possible to focus the laser spot with even greater precision.
   • This allows data to be packed more tightly and stored in less space, so it’s possible to fit more data on the disc even though it’s the same size as a CD/DVD. Blu-Ray disks of today are capable of storing upto 128 GB of data.

System Bus

The system bus (or the bus) is an electronic pathway composed of connecting cables and that connects the major components of a computer system. Through system bus, data and instructions are passed among the computer system components.

• The data carrying part of system bus is called data bus.
• The control instruction carrying part of system bus is called control bus.
• The memory address carrying part is called address bus.
• A separate type of bus called I/O Bus connects the Input, Output and other external devices to the system.

Mobile System Organization

Modern mobiles are tiny computers in your hand. Although they have less computing power compared to their bigger versions, they handle diverse type of applications such as making calls through radio signals, offering camera utilities, handling touch sensitive screen, display audio/video/graphical content but having little battery based power etc.

Mobile Processor

This is the brain of a smartphone. The CPU receives commands, makes instant calculations plays audio/video, stores information and sends signals throughout the device.

The CPU of a mobile system has majorly two sub-processor types Processing Unit.

1. Communications Processing Unit : This subsystem is responsible for making and receiving phone calls on a mobile handset. It has a digital signal processor that helps it work with RF Transceiver and the Audio subsystem.
   • Radio Signal Management Unit is responsible for connecting SIM (which provides a type of modem) to the base stations through radio signals (3G/LTENG based cellular networks).
2. Applications Processing Unit (APU). This subsystem is responsible for governing controlling all types of operations taking place on a mobile system by running various types of mobile applications (apps).

Display Subsystem

This system is responsible for providing display facilities, touch sensitive interface and touch sensitive keyboards.

Camera Subsystem

This subunit is designed to deliver a tightly bound image processing package and enable a improved overall picture and video experience.

It has an integrated Image Signal Processor ensures things like instant image capture, high-resolution support image station, and other image enhancements

Mobile System memory

A mobile system memory is compromised of two memories:

1. RAM (Random Access Memory): It is the work memory of your mobile system.
   • The installed mobile apps, when run, are first loaded in the RAM and then executed. These apps remain in the RAM after you are no longer using them and then they are shifted to background.
2. ROM (Read Only memory): The ROM or Read Only Memory is a part of mobile system’s internal storage and it is not accessible for users to write on and is thus referred to as Read Only Memory.
   • The ROM is basically Flash memory or technically EEPROM (electrically erasable and programmable read-only memory)

This subunit is designed to deliver a tightly bound image processing package and enable a improved overall picture and video experience. It has an integrated Image Signal Processor ensures things like instant image capture, high-resolution support image station, and other image enhancements

Storage

The external storage of a mobile system is also called expandable storage. It comes in the form of SD cards, or micro SD cards etc. It is the storage which can be removed easily by you and can be used for storing pictures, music, videos and the likes.

To an extent, even the cloud storage can also be categorized as external storage.

Battery – Power Management System

This subsystem is responsible for providing power to a mobile system. The mobile systems work on limited power provided through an attached battery unit.

This subsystem has a battery management system that works with a battery charger and a battery unit, and provides power to the mobile system in required form.

System Software

Instructions are provided to the computer through software. The software that controls internal computer operations (viz. reading data from input devices, transmitting processed information to the output devices, checking system components, converting data/instructions to computer understandable form etc.) is known as system software. The system software can further be classified into two categories:

1. Operating System
2. Language Processor

Operating System

An operating system is an important component of a computer system which controls all other components of the computer system.

Major components of a computer system are:

1. The Hardware
2. The Operating Software
3. The application program routines (compiler, linkers, database management systems, utility programs)
4. The Humanware (Users)

• Application program routine: the ways in which these resources are used to solve the computing problems of the users.

• The OS controls and coordinates the use of the hardware among the various application programs for various users.

• There are different types of operating systems available today to cater to varied type of requirements. Example: Single user OS, Multiuser OS, Time sharing OS, Real time OS, Multiprocessing OS, Distributed OS etc.

Language Processors

A special type of computer software that can translate the source code into an object code or machine code.

There are three types of language processors:

1. Assembler : This language processor converts the program written in assembly language into machine language.
2. Interpreter : An interpreter is a type of system software that translates and executes instructions written in a computer program line-by-line, unit by unit etc.
3. Compiler : A Compiler is another type of system software that translates and executes computer program in one go.

Application Software

These are the programs written by programmers to enable computer to perform a specific task such as processing words, inventory control, handling calculations and figures, medical accounting, financial accounting, result preparation, railway reservation, billing etc.

Application software can further be subdivided into four categories:

1. Packages
2. Utilities
3. Customised Software
4. Developer Tools

Packages

As applications may be numerous (from thousands to millions of them), it is not feasible to design software for each one of them. Rather some general software are designed that may be used by individual users in the manner it suits their needs and requirements. Such general-application software are known as packages. Some major and most common categories of general application software (packages) are:

• Word Processing Software
• Spreadsheets
• Desktop Publishing Software
• Graphics, multimedia & presentation applications.
• Database Management Systems

Utilities

These are those useful software that ensure smooth functioning of the computer.

Some of the important utilities are mentioned below:

1. Text editor: Creating, and editing text files.
2. Backup Utilities: Utility program facilitates the backing-up of disk. Back-up means duplicating the disk information so that in case of any damage or data-less, thus backed up data may be used.
3. Compression Utility: This utility program facilitates compression of files. Large files can be compressed so that they take less storage area.
4. Disk Defragmenter: A file is fragmented when it consumes to large for your computer to store in a single location on a disk.
   • When this happens, your computer splits the file up and stores it in piece. You can use fragmented files, but it takes your computer larger to access them.
   • Disk Defragmenter utility program speeds up disk access by rearranging the files and Free space on your computer
5. Antivirus Software: This utility program ensures virus-free work environment.
   • A computer virus is a malicious computer program that disrupts normal functioning of a computer.
   • An antivirus software scans your disk for viruses and removes them, if any virus is found.
   • Moreover, some antivirus software remains present in memory all the time so that they can detect the viruses (as soon as they occur) and counterattack them.

Business Software

This type of software is specifically created software according to a business requirements. This type of software is developed to meet the general requirements of a business.

There are many readymade business software that can cater to a variety of business needs.

• However, such software cannot be directly installed at any other user’s workplace as the requirements of the second user may differ from the first and the software may not fit in the requirements of the new user.

Software Libraries

When programmers develop software and programs, they have a prewritten set of code/functions, classes, scripts etc available to do a variety of tasks, which they can use directly in their code. These predefined sets of codes are called software libraries.

The software libraries combine codes/ functions/scripts/classes etc., on the basis of their common domain. In order to use the rewritten functionality, a programmer needs to add that libraries to its code.

1. NumPy :It provides an abundance of useful features and functions for operations on numeric arrays and matrices in Python.
2. SciPy : Contains modules for Linear algebra, optimization, integration and statistics.
3. Panda : It is a python framework to handle “labelled” and “relational ” data.