storage devices presentation parts of computer

Storage devices used in a computer

1. 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.

2. T ypes of Memory Primary Memory/Main Memory Secondary /Auxiliary memory Cache Memory

3. Primary Memory (Main Memory) Primary memory holds only those data and instructions on which the computer is currently working . It is a direct access storage device, consisting of a number of storage locations. Each locations in the storage has a unique number called address. It is generally made up of semiconductor device . It is fixed on the motherboard of the computer . It is divided into two subcategories RAM and ROM.

4. Characteristics of Main Memory It is known as the main memory . Usually volatile memory . It is temporary. It is the working memory of the computer. Faster than secondary memories . Takes few seconds for the CPU to access RAM. A computer cannot run without the primary memory . It is Costly. It has limited storage capacity .

5. RAM ( RANDOM ACCESS MEMORY) This memory is also known as Read/write memory. It is the computers working memory where it stores the programs and data that are being used at a given time. The contents of RAM can be changed because it only stores programs and data temporarily. When the computer is turned off, the contents of RAM are lost.

6. ROM (Read Only Memory) The written program in ROM can be read only. Any program or information cannot be stored in it. The program and data stored on ROM are permanent and cannot be changed . When the computer is switched off the contents of ROM are not lost. The memory which is not wiped clean, when the computer is turned off, is called non-volatile memory . The main use of ROM chips in a computer is to store the program that runs when the computer is turned on , this will then load the operating system from disk.

7. RAM RAM is a temporary memory. Volatile memory. Read and write. Contents are lost when power is off. ROM ROM is permanent in nature Non-volatile memory. Read only. Contents are remain stored even if power is turned off.

8. Secondary Memory This type of memory is also known as external memory or non-volatile . It is permanent in nature. It is slower than the main memory. These are used for storing data/information permanently . It is used to store the different programs and the information permanently. It holds the information till we erase it. The contents of secondary memories are first transferred to the main memory, and then the CPU can access it. Different types of secondary storage devices are : HDD, Compact Disc, DVD, Pen Drive etc .

9. Characteristics of Secondary Memory These are magnetic and optical memories. It is known as the backup memory. It is a non-volatile memory. Data is permanently stored even if power is switched off. They have more storage capacity than Primary memory. Slower than primary memories . Easy to transfer data from one computer to another. Secondary memory can be reused again and again. We can store new information and delete obsolete information.

10. Hard Disc Computer Hard Disc is the main storage device of the computer which is fixed inside the CPU box. Its storage capacity is very high that varies from 200 GB to 3 TB. As it is fixed inside the CPU box, it is not easy to move the hard disc from one computer to another. A hard disc contains a number of metallic discs which are called platters(arranged parallel one by one) . Information is recorded on the surface of the platters in a series of concentric circles . These circles are called Tracks . For the purpose of addressing information, the surface is considered to be divided into segments called Sectors . This division helps in the proper organisation of data on the platter and helps in maximum utilisation of the storage space.

11. HARD DISK

12. Compact Disc(CD) It is a thin plastic disc coated with metal . Computer can read and write data stored on it . This is an optical storage device with a storage capacity of up to 700 MB and it can store varieties of data like pictures , sounds, movies, texts etc.

13. Digital Versatile Disc (DVD) It is an optical storage device which reads data faster than a CD . A single sided DVD can store data up to 4.7 GB , i.e , around 6 times than that of CD. Though DVDs look just like CDs , they can hold much more data , for example, a full length movie .

14. Pen drive It is an electronic memory device popularly known as pen drive in which data can be stored permanently and erased when not needed . I t is a portable storage device that can be easily connected and removed from the CPU to store data in it . Its capacity can vary form 2 GB to 256 GB.

15. Primary Memory It is known as main memory/Internal memory/Temporary memory. It is Volatile Memory. It has limited storage capacity. It takes few nano -seconds for the CPU to access RAM. RAM is costlier than Secondary Memory Examples : RAM, ROM Secondary Memory It is known as Auxiliary/ External/ Permanent Memory. It is Non-volatile memory. It has large storage capacity. It takes several milli seconds to access secondary memory. It is cheaper than RAM. Examples: Pen Drive, HDD,CD,DVD

16. Cache Memory The cache is a special high-speed storage mechanism. It can be either reserved section of main memory or an independent high speed storage device. Whenever, some data is required, the CPU first looks in the cache, if it is there or not. If the data is found in cache, CPU does not access memory and hence the process becomes very fast.

17. Memory Units Data in the computer’s memory is represented by the two digits 0 and 1 . These two digits are called Binary Digits or Bits. A bit is the smallest unit of computer’s memory(0 or 1). To represent each character in memory , a set of 8 binary digits is used . This set of 8 bit is called a Byte . So , one Byte is used to represent one character of data . Bits=0,1 1 Byte= 8 bits(e.g,11001011 ) 4 bits= nibble

18. Cont.. To represent a large amount of data in memory, higher data storage units are used like KB(Kilobyte), MB(megabyte), GB(Gigabyte), TB(terabyte ), PB( PetaByte ), etc. But all these unites are formed with the set of bytes like, 1 KB(kilobyte) = 1024 Bytes 1 MB(megabyte) = 1024 KB 1 GB(Gigabyte) = 1024 MB 1 TB(Terabyte) = 1024 GB 1 PB( PetaByte ) = 1024 TB