9th Class Computer: chapter 4 Storage Devices Short Questions Answer
9th Class Computer: chapter 4 Storage Devices Short Questions Answer
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The data in direct access storage can be accessed directly. The required data can be accessed if its address in known. The require data is searched very quickly. Magnetic disc and CD are important examples of direct access storage.
The main memory is known as working area of the computer. It is very fast but limited in capacity. Most computer have enough of memory to store a few million characters.
A computer can not work with out main memory. A program first loaded in the memory before it is executed. The result and data of calculation are also stored in the memory. The computer needs main memory to execute instruction and store their result temporarily.
Memory is volatile but storage in not volatile. Memory is faster and more expensive than storage. memory is generally smaller in size than storage. The capacity of memory is less than storage. Memory directly connected to CPU but storage is not directly connected to CPU.
RAM stands for random access memory. It is used to store data and instructions temporarily. Most desktop computer typical have 4GB of RAM or more.
RAM is known as directly access memory. It means that each byte in the memory can be access directly. Any location in the RAM can be accessed in same amount of time. RAM is used to store data and instructions temporarily.
The main memory is called random access memory RAM called because each memory cell of this memory can be accessed randomly i.e with out any sequence and order.
RAM is temporary memory. When the power is turned off, The information in the memory is lost. That is why it is called volatile memory.
DRAM is most commonly used technology. It is least expensive kind of RAM. It required an electric current to maintain their electrical state. It is recharge and refresh again and again to maintain its data.
The processor can not access the data of DRAM when it is being refreshed. That is why it is slow.
SRAM is faster than DRAM but it is more expensive. It does not need to be refreshed. It is normally used to build a fast memory known as cache memory. Cache memory is very small in size. It is used to increase the performance of computer.
DRAM holds its data dynamically. It does not hold it definitely. Each DRAM memory cell must be constantly refresh to keep data in DRAM. SRAM does not required refreshing. It hold the data indefinitely as long as computer remain on. It is faster than DRAM but it is more complex.
DRAM uses more power because it is recharge and refreshed again and again to maintain data.
The instruction in the ROM prepare the computer for use. These content of ROM can only be read but can not be change or delete. It is not possible to write new information or instructions in ROM. It stores data and instructions permanently.
RAM is a type of volatile memory. The content in RAM are not stored permanently. ROM is non volatile memory. Its contents can only be read and new information can not be written.
ROM stored data and instructions permanently. When the power is switched off, The instruction stored in ROM are not lost. Therefore ROM is called non volatile memory.
PROM is initial blank. The user and manufacturer can write data and programs on it using spacial device. The user can write data and instruction on it only one. If there is any error in writing the instructions, the error can not be removed from PROM. The chip become unusable.
This form of ROM is initially blank. The users or manufacturer can write data and program on it by using special device. The data and program written on it can be erased using ultraviolet rays. The user can then write new programs.
The user can erase and writ instruction in EEROM using electrical devices. The user can erase its content by electrically if any error occurs writing instructions. The content of EEPROM can be modified easily.
There are different factor that affect the storage speed. Access time is a time in which a device locate an item on a storage medium. It is measured in millisecond. Data transfer rate is amount of data a storage device move per second from storage medium to computer. Higher number indicate the higher transfer rate.
Storage capacity is the maximum amount of data that can be stored in a storage medium. It is measured in megabyte MB, gigabyte GB or terabyte TB. Storage capacity is directly related to storage density that is amount of data that can be stored in given area of storage medium such as disk surface. The higher the storage density allow more data to be stored.
Storage device categorized by the type of operation they perform, the method use to access the information, the technology they use and their capacity and speed.
1 gigabyte = 2×10^30 bytes= 2000000000= about one billion bytes.
The data stored on floppy disk can be read with floppy disk drive. The read/write head of disk drive is used to read and write data on the floppy disk.
Hard disk is main storage device in computer to store programs and data permanently. It is also known as hard disk drive HDD or Hard drive HD. Most personal computer have at least one hard disk drive. The capacity of hard disk is up to 8 TB or more.
Hard disk drive is the preferred type of main storage for most personal computers for three reasons. First it provide large storage capacity. Second it provides fast access to files. Third, a hard disk is economical and reliable storage media.
hard disk consist of different circular disk called platters. The platters stacked on one an other in a sealed case. Each platter has two read/write heads, one for each side. The hard disk also has arms they move read/write head to the paper location on the platter to read ans write data.
The performance of hard disk measured by its data rate and seek time. Data rate is the number of bytes per second that are delivered to CPU by the drive. Seek time is the time that is used to move the head to the required track after reading the address.
Magnetic disk storage is the most widely used storage media. The magnetic disk use magnetic material to store data, instructions and information the disk surface. A disk must be formatted before it can be used. The formatting process prepare disk for storing data. It creates tracks and sectors on the disk.
The data stored on the surface of plotter in sector and tracks. A track is a concentric circle that is further divided into sectors. A track is typically divided into 8 sectors. A specter usually contains a fix number of bytes such as 512 bytes.
Disk drive used to read and write data on disk. It has one or more read and write heads to read and write data. There are different type of disk drives for different type of disk. For example a floppy drive read/ write the data on floppy disk.
Formatting is a process of preparing a disk to store data. This process creates tracks and sectors on disk. Each track further divided into sectors.
A drive marks the tracks and sectors on disk during low level formatting. It is usually done by the manufacturer of the disk. This process writes the starting and points of each sector on the plotter. It prepare the disk to store data.
The information about files written on the disk during high level formatting. The information is known as file allocation table FAT. This process also prepare the disk to store data.
Compact disk is widely used storage media today. It is usually known as CD-ROM. It can stored more then 700MB of data. It is very useful for storing audio and video data. The data stored in CD-ROM can not be deleted or change. CD-ROM is portable storage device.
CD-ROM stand for Compact Disk Read Only Memory. The data store on CD-ROM can only be read. It can not be deleted or changed. It can store up to 700MB data.
CD-ROM is mostly used to store photos and audio. It is often use to distribute new application software and game.
It is the least expensive way to store data and information. CD-ROM discs are durable and easy to handle. Information can be store on CD-ROM for many years.
Magnetic tape is an old storage media. It consist of thin ribbon of plastic. The tape is coated with magnetic material. A tape drive used to access magnetic tape to write and read data.
The magnetic tape is divided into segments. Each segment mark magnetically by a gap when disk is formatted. Each segment contains many tracks. The first eight bit are used to store data. The last bit used to store parity data.
Bit stands for binary digit. It is the smallest unit of data. that can be used by computer. It can be either 0 or 1. Byte is collection of 8 bit. A byte is required to store one characters.
The time used to move the head of disk to required track after reading the address is called seek time.
A byte usually represent one character.
The basic unit of data storage are bit, byte, kilobyte, megabyte and gigabyte.
128 Bits = 16 bytes.
64 bytes = 64*8 = 512 bits.