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Memory A memory is just like a human brain. It is used to store data and instructions. Computer memory is the storage space in the computer, where data is to be processed and instructions required for processing are stored. The memory is divided into large number of small parts called cells. Each location or cell has a unique address, which varies from zero to memory size minus one. For example, if the computer has 64k words, then this memory unit has 64 * 1024 = 65536 memory locations. The address of these locations varies from 0 to 65535. It is of two types: a) Primary Memory b) Secondary Memory a) Primary Memory( Main Memory): Primary Memory is the Main memory of the Computer System. It is directly accessed by the CPU(Central Processing Unit). It also referred as \"Internal Memory\". The use of this memory is to process the inputted data. This memory is necessary for booting of a computer. Primary memory holds only those data and instructions on which the computer is currently working. It has a limited capacity and data is lost when power is switched off. It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instruction required to be processed resides in the main memory. It is divided into three subcategories ie. i) RAM ii) ROM iii) Cache i) RAM : It is acronyms for Random Access Memory. It is volatile(Temporary) Memory. The data stored in RAM will automatically erased when power goes off. RAM stores the currently processed data from the CPU and sends them to the graphics unit. -> SRAM -> DRAM ->SD-RAM Static RAM Dynamic RAM Statically Dynamic RAM (Refresh) (No refresh) (Refresh) ii) ROM : It is acronyms for Read Only Memory. It is permanent Memory. There is no loss in data if electricity goes off. Rom is divided into: - PROM (Programmable Read Only Memory) Once the data are loaded, can’t deleted at any condition. - EPROM(Erasable Programmable Read Only Memory)

The data on this EPROM will be deleted using UV (Ultra Violet Rays) - EEPROM(Electrically Erasable Programmable Read Only Memory) The data on this EEPROM will be deleted using Electricity. iii) Cache Memory: It is a memory between the CPU and RAM. It enhances the speed of processing unit. It minimizes the computer Idle Time. If data is under Cache Memory, then it is called Cache \"hit\" otherwise called Cache \"Miss\". Cache memory is a very high speed semiconductor memory which can speed up the CPU. It acts as a buffer between the CPU and the main memory. It is used to hold those parts of data and program which are most frequently used by the CPU. The parts of data and programs are transferred from the disk to cache memory by the operating system, from where the CPU can access them. 32bits CPU = 32/8 byte = 4 Bytes 64-bits= 84/8 byte = 8 Bytes b) Secondary Storage( Secondary Memory): Secondary Memory is use to store huge amount of data. In Secondary Memory we can store our personal data for future use. It’s slower than Primary Memory. It is cheaper than Primary Memory. However, it can save a substantial amount of data, in the range of GigaByte(GB) and TeraByte(TB). This memory is also called Secondary Storage or Backup Storage or Mass Storage Media. This type of memory is also known as external memory or non-volatile. It is slower than the main memory. These are used for storing data/information permanently. CPU directly does not access these memories, instead they are accessed via input-output routines. The contents of secondary memories are first transferred to the main memory, and then the CPU can access it. For example, disk, CD-ROM, DVD, etc.

Types of Secondary Memory: 1) Magnetic Tape 2) Magnetic Disk 3) Optical Disk 4) Flash Drive 1) Magnetic Tape Magnetic tape is a serial(sequential) access storage device which allows us to store huge amount of data. This is old technique to store data. The magnetic tape is made up of special type of plastic which is coated with Magnetic material(like Iron Oxide). The data stored in Magnetic Tape as Track and Sector. Magnetic Tape records data in two format ie. Single side and double side. For Example, Cassette used in Walkman. VCR cassettes etc. 2) Magnetic Disk Magnetic Disk is a circular Disk made up of Plastic/Fiber/Aluminum/Glass. It is coated with Magnetic Material (like Iron Oxide). It is use to store large volume of data than Magnetic Tape. It is based on Random Access Technique. It uses a Magnetic Disk Player (Called Drive) which is able to read data from the Magnetic Disk using Head. For example, Floppy Disk, Hard Disk etc. a) Floppy Disk (1.44MB) Floppy Disk is a Magnetic Disk. It was one of the popular storage devices in 1990’s. It is made up of a special plastic called myler coated with Magnetic Material like as Magnetic Disk. It is jacketed with Solid Plastic. Its capacity is 1.44 MB. In floppy Disk,

data is stored as Track and Sector. Floppy Disk is played(Operated) by a device called Floppy Drive. Today, we don’t use it. b) Hard Disk Drive(HDD) Hard Disk Drive is also a Magnetic Disk. It is very popular storage device from beginning. It is also called Solid Disk due to its structure. It contains platters made up of Aluminium plates coated with magnetic material. It contains a motor connected with spindle to rotate platters. It has its drive attached. Hard Disk Drive has a R/W(Read/Write) Head from which data is inserted, updated, viewed or manipulated into Hard Disk Platters. HDD also use Track and Sector to store data. It uses Random Access Technique to store data which makes faster access of data searching. The data on platters becomes bad sector due to any scratch or crack. Scan Disk is a software to search Bad Sector from Hard Disk And Disk Defragmentation is a s/w to arrange data in good track/sector. SSD(Solid State Drive) is also HDD for Today’s Laptop. It is faster than Normal HDD due to it’s mechanism. HDD has 3600 RPM-7200 RPM while SSD has MBPS speed. Generally, Hard Disk Drive is use to store Computer Operating System and File Systems. 3) Optical Disk

Optical Disk is a round shaped Disk made up of plastic/fiber/glass coated with higher reflecting material. It uses Optical Mechanism to read/write data. It uses Laser beam light technique to Read/write data. Optical Disk has a single Track but multiple Sector. The data recorded in it is Sequential Technique. Data are stored on Pit (0,1 format). Optical Disk was firstly introduced by Sony Company for their Music Data. Types of Optical Disk a) CD-R b) CD-R/W c) DVD d) Blue Ray Disk a) CD-R : It acronyms for Compact Disk Recordable. It was first Disk developed in the history of Optical Disk. It’s normal capacity is 600-700 MB. b) CD-R/W : It acronyms for Compact Disk Re-Writable. It’s normal capacity is 600- 800 MB. c) DVD : It acronyms for Digital Versatile Disk. It is more powerful than CD. It’s normal capacity is 4 GB – 8 GB. d) Blue Ray Disk: It is very popular disk today. It’s normal capacity is 10GB- 30 GB. 4) Flash Drive: Flash drives are automatic drives that automatically play & Plug. These devices are made up of Chips Technology. A flash drive is a small, ultra-portable storage device which, unlike an optical drive or a traditional hard drive, has no moving parts. Flash drives connect to computers and other devices via a built-in USB Type-A or USB-C plug, making one a kind of combination USB device and cable. These are very small but has great storing capacity. For Example, Pen Drive, Memory Card Etc.