Unit 2 - Basic computer organisation

 CBSE Revision Notes

Class-11 Computer Science (New Syllabus)
Unit 2: Computer Systems and Organisation (CSO)

Basic computer organisation

Computer organization is concerned with how the various components of computer hardware operate and they are interconnected to implement the architectural specification. Let’s discuss various components of computer organization.

Computer system: A computer system allows users to input, manipulate and store data. Computer system typically includes a cpu, Hard disk, Ram, monitor, keyboard, mouse and other optional components. All of these components also can be integrated into all-in-one units, such as laptop computers.

During the data processing stage, instruction sets, known as programs, are provided to let the system know what to do with the entered system data. Without these programs, the computer would not know how to process data that enters the system, and the data might be discarded. Known as a stored program computer, this type of computer is the most common in use today. It is very flexible, as it can process any task by loading a program from storage. Computer systems can work by themselves or access other devices that are external or connected with other computer systems.

Mobile System: Now a day’s mobile system has taken over computers it can perform tasks that a computer can perform and can easily be carried in our pockets. Mobile systems are becoming powerful day by day. It’s a single unit made of cpu , ram and memory storage, Battery all these things are embedded on motherboard.

Let’s discuss some of the components of computer system

CPU: CPU is called brain of the computer. Its primary function is to execute programs. In addition CPU also controls operation of all other components such as Input and output devices, memory.

Alternately it’s referred to as a processor, central processor, or microprocessor. There are two major parts of a CPU

  1. Arithmetic logical Unit (ALU): ALU of a computer system is where actual execution of instruction takes place during the processing operation. To be more precise all calculations and comparisons are done at ALU.
  2. Control unit (CU): A control unit (CU) handles all processor control signals. It directs all input and output flow, fetches code for instructions from micro programs and directs other units and models by providing control and timing signals. A CU component is considered the processor brain because it issues orders to just about everything and ensures correct instruction execution.

    CU functions are as follows:
  • Controls sequential instruction execution
  • Interprets instructions
  • Guides data flow through different computer areas
  • Regulates and controls processor timing
  • Sends and receives control signals from other computer devices
  • Handles multiple tasks, such as fetching, decoding, execution handling and storing results

Memory: Memory is referred as RAM or primary memory. RAM stores programs and data currently being used by the CPU. The maximum amount of programs and data that a piece of RAM can store is measured in units called bytes. Modern PCs have many millions, even billions, of bytes of RAM, so RAM is measured in units called megabytes (MB) or gigabytes (GB). An average PC will have from 4 to 8 GB of RAM, although PCs may have more or less. Each piece of RAM is called a stick. One common type of stick found in today’s PC is called a dual inline memory module (DIMM).

Hard Disk: A hard drive stores programs and data that are not currently being used by the CPU. Although RAM storage is measured in megabytes and gigabytes, a PC’s hard drive stores much more data than a typical PC’s RAM hundreds of gigabytes to terabytes. A terabyte is 1000 gigabytes. An average PC has one hard drive, although most PCs accept more. Special PCs that need to store large amounts of data, such as a large corporation’s main file-storage computer, can contain many hard drives 8 to 16 drives in some cases.

The two most common types of hard drives seen in today’s PCs are the older Parallel Advanced Technology Attachment (PATA) and the more modern Serial Advanced Technology Attachment (SATA). PATA drives use a ribbon cable very similar to the one used by floppy drives, whereas SATA drives use a very narrow cable. Most motherboards only come with SATA connections, but if you look around, you can find one that supports PATA as well.

Input output: There are many devices which are used for input and output. Let’s see them one by one Input devices are those devices which give input to the computer for example keyboard, mouse, joystick etc.Output devices are those devices that gives result to end user for example printer, monitor etc.

Battery: Battery is usually used to supply uninterrupted power supply to the computer battery is present in the form of UPS (Uninterruptible power supply). All UPS are measured in both watts (the true amount of power they supply in the event of a power outage) and in volt-amps (VA). Volt-amps is the amount of power the UPS could supply if the devices took power from the UPS in a perfect way. UPS provides perfect AC power, moving current smoothly back and forth 60 times a second. Power supplies, monitors, and other devices, however, may not take all of the power the UPS has to offer at every point as the AC power moves back and forth, resulting in inefficiencies. If your devices took all of the power the UPS offered at every point as the power moved back and forth, VA would equal watts.

There are two main types of UPS: online, where devices are constantly powered through the UPS’s battery, and standby, where devices connected to the UPS receive battery power only when the AC sags below ~80–90 V. Another type of UPS is called line-interactive, which is similar to a standby UPS but has special circuitry to handle moderate AC sags and surges without the need to switch to battery power.

Power: Your PC uses DC voltage, so some conversion process must take place before the PC can use AC power from the power company. The power supply in a computer converts high-voltage AC power from the wall socket to low-voltage DC. The first step in powering the PC, therefore, is to get and maintain a good supply of AC power. Second, you need a power supply to convert AC to the proper voltage and amperage of DC power for the motherboard and peripherals. Finally, you need to control the by-product of electricity use, namely heat.