Unit 1.4 Computer Hardware The physical parts of a computer which can be seen, felt and touched are called computer hardware. Computer hardware is important component of computer system. The user can perform a task by using a set of instructions through the computer hardware. So, the combination of computer hardware and software makes up a full functioning computer system that performs specific task. Motherboard, microprocessor, RAM, ROM, hard disk, pen drive, keyboard, scanner, monitor, etc. are the examples of computer hardware. a. Motherboard Motherboard is called PCB (Printed Circuit Board) or system board or main circuit board. All parts of computer system like microprocessor, slots, ports etc. are mounted on motherboard. So, it is also called backbone of computer system. It also connects important chips like ROM chip, Network chip, sound card, etc. Motherboard Function of motherboard a. There are different slot which joins modem, TV card, etc. in motherboard. b. Motherboard helps in data communication among different hardware. c. BIOS (Basic Input Output System) programs are stored in ROM and ROM is Computer Science : Grade 9 29 attached to motherboard to boot the system. b. Microprocessor Microprocessor is an important part of computer hardware. Computer cannot perform the task without a microprocessor. So, it is also called the brain of a computer. Microprocessor gets data and instructions from various hardware and processes it with the help of software to produce information as an output to the user. It can do arithmetic calculation and logical comparison between two numbers. Nowadays, a trillion of instructions can be processed within a second. Microprocessor Working of Microprocessor i. Fetch The user can give data and instructions which is stored in RAM. Microprocessor receives data and instruction according to necessity and requirement which is known as fetch. So, fetch means get instruction from memory. ii. Decode The main function of microprocessor is to change fetched instruction into decoded instruction. The given instruction is separated for arithmetic or logical calculation. So decode means to decide what the instruction means. iii. Execute Microprocessor can perform the main task in this unit. For example, ALU is used for mathematical calculation. So, execute means to carry out the instruction into action. iv. Write back 30 Computer Science : Grade 9 Microprocessor processes the instructions and produces result which is transferred to memory for storage. This is called to write back. The complete cycle of four units as fetch, decode, execute and write back of microprocessor for processing the instruction is called the instruction cycle. c. Memory The physical part of a computer that store data, information and software temporarily or permanently is called memory or storage. Storage device or memory device is used to store data and information. The three types of memory are as follows i. Primary memory, ii. Secondary memory and iii. Cache memory. Register High cost Cache memory Low cost Fast access time High disk storage Low storage capacity Main memory capacity Slow access time Magnetic Disks Magnetic Tapes Memory Hierarchy i. Primary memory The main memory is called primary memory. Primary memory stores data temporarily or permanently. It stores information during the processing of raw data. The two types of primary memory are: RAM (Random Access Memory) ROM (Read Only Memory) Computer Science : Grade 9 31 RAM (Random Access Memory) RAM is the main memory of computer system. It is volatile or temporary memory. Volatile memory means that RAM loses its information when the computer is switched off or faces power failure. So, it needs constant power supply to hold currently running program. It is also called semiconductor memory. It is read/write memory. There are two types of RAM. They are SRAM and DRAM. SRAM: SRAM stands for Static Random Access Memory. It does not need periodic refreshing to preserve the information. It is faster and expensive than DRAM. Characteristic of Static RAM ⚫ Long life and no need to refresh ⚫ Faster and used as cache memory ⚫ Large size and expensive ⚫ Expensive and high power consumption DRAM: DRAM stands for Dynamic Random Access Memory. It needs a periodic refreshing to preserve the information. It is slower and cheaper than SRAM. Characteristics of Dynamic RAM ⚫ Short data lifetime and needs to be refreshed continuously ⚫ Slower as compared to SRAM and used as RAM ⚫ Smaller in size and less expensive ⚫ Less power consumption RAM ROM (Read Only Memory) ROM is a non-volatile or permanent memory. Non-volatile means never loses data in ROM. It stores data permanently even when the computer is switched off or power failure. It is read-only memory because the programs in ROM are stored at the time of 32 Computer Science : Grade 9 manufacture of the computer. It is fixed on motherboard. The three types of ROM are PROM, EPROM and EEPROM. PROM PROM stands for Programmable Read Only Memory. Once a program has been written onto the PROM, it remains there forever and can't be updated and deleted. EPROM EPROM stands for Erasable Programmable Read Only Memory. It can be erased by ultraviolet light and reprogramming. EEPROM EPROM stands for Electrical Erasable Programmable Read Only Memory. It is called flash ROM. It can be erased by exposing it to an electrical charge and reprogramming. It is also called hybrid memory with a combined feature of RAM and ROM. ROM Firmware Firmware is software that's embedded in a piece of hardware. So, the firmware is software for hardware. CPU Register CPU Register is a small storage memory, located inside the microprocessor and has a high speed data transfer rate. It stores data and instructions used by the microprocessor. Cache Memory Cache memory is also like CPU Register, located inside the microprocessor but has high storage capacity than CPU Register and high-speed data access rate. It also stores the data and instruction used by the microprocessor. So, it stores very active data and instructions temporarily during processing. If required data and instruction are not found in cache memory then the searching is done in primary memory. Computer Science : Grade 9 33 ii. Secondary Memory Secondary memory is also called auxiliary memory or backup memory. These memories are used to store data and instructions permanently for future use. CD/DVD, pen drive, hard disk, etc. store data and instruction for future. The various types of secondary memory are Magnetic Tape, Hard disk, SSD (Solid State Drive), Optical Storage Disc, Pen drive, etc. a. Magnetic Storage Computer systems need to store data in digital format. One of the most widely used types of digital data storage is magnetic storage. This refers to any type of data storage using a magnetized medium. Several types of magnetized media are used in computer systems, including magnetic tape, floppy disks, Super disks, hard disks, etc. Magnetic Tape Magnetic Tape is a usable secondary storage device to store and retain a large volume of data. It is made up of a plastic strip of which one surface is coated with magnetic ink. Analog and digital data are stored in magnetic tape. Normally, minicomputer, mainframe computer, large scale business organization server, etc. uses magnetic tape for backup data and information. Magnetic tape driver are used to store and retrieve the data and information from magnetic tape. The main important function of magnetic tape is to store data safely for a long period of time. Magnetic Tape and Tape Drive Hard Disk Hard disk is commonly used storage device. It stores large amount of data and information permanently. It is also called fixed disk. It is made of aluminium materials 34 Computer Science : Grade 9 and the surface is coated with the ferromagnetic element. Circular metal discs also called platters to rotate while writing or reading the data and information into them. It stores a large amount of data on hard disk. The speed of the hard disk is measured in rpm (revolutions per minute). The hard disks with 5400 rpm or 7200 rpm are generally used in present-day computer system. Hard disk capacity Hard disk must be formatted before use. There are thousands of track on the surface of hard disk. So, each track is divided into various sectors. Each sector stores 512 bytes. Header is used to read and write on hard disk. The storage capacity of hard disk is determined from number of disk or platter it contains and their density. Hard Disk Track and Sector SSD (Solid State Drive) Hard disk can be replaced and upgraded by SSD (Solid State Drive) as new technology. Semiconductor chips are used to store data in SSD. The speed to read and write data is greater than hard disk. So its price is more expensive than hard disk. Laptop, notebook, ultra book, etc. uses SSD as storage device. Its storage capacity is about 4 TB but various companies are trying to develop SSD with high storage capacity. It is more costly than HDD (Hard Disk Drive). Computer Science : Grade 9 35 Solid State Drive Differences between SSD and Hard disk S.N. Hard disk SSD 1 It is heavier than SSD. It is lighter than hard disk. 2 Its storage capacity is 500 GB to Its storage capacity is 1 TB to 4 TB. 100 TB. 3 It is cheaper than SSD. It is more expensive than hard disk. 4 It takes 6-7 watt electricity. It takes 2-3 watt electricity. The file writing speed is 50-120 The file writing speed is 200-550 MB/S 5 MB/S (megabyte per second) (megabyte per second) 6 It is made up of aluminium material. It is made up of semiconductor microchip. External Hard Drive The working principle of hard disk is similar to that of internal hard drive but it is not placed inside CPU casing.