Sir Sadiq s computer notes for class IX. Chapter no 4. Storage Devices

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2 Q: Define Computer memory or storage. Ans: Memory: Memory refers to the place where data is kept for later use. For example, a human being has a memory where he/she stores the things that can be recalled whenever required. In the same way, computer storage or memory refers to the media and methods used to keep information available for later use. Q: What is primary (Main memory) and secondary memory? Ans: Primary memory: Primary memory comes in the form of chips located on the motherboard so that data can travel quickly between memory and CPU. There are two basic types of primary memory: 1. RAM (Random Access Memory) 2. ROM (Read Only Memory) Secondary memory: Secondary storage is called Auxiliary storage / external memory that is used to store large quantities of data for longer period of time and that is not currently being processed. This is the stuff filed away, but ready to be pulled out when needed. It is nonvolatile (power off does not erase data). It includes Floppy disk, Hard disk, CD ROM and magnetic tape. Q: Write a note on RAM. Ans: RAM: RAM stands for Random Access Memory. It is a type of computer memory that can be accessed randomly. The term RAM also refers to Read and Write memory. Old data and programs can be wiped out from the RAM chips and new ones can be written on the same. It is volatile which means that it requires a steady flow of electrically to maintain the contents. As soon as the power is turned off, whatever data was there in RAM is lost. It is also called temporary memory. There are two basic types of RAM. Dynamic RAM (DRAM) Static RAM (SRAM) Q: What is the Difference between dynamic and static RAM? Ans: DRAM: DRAM (Dynamic RAM) is the most common type. Dynamic RAM needs to be refreshed thousands of times per second. It uses capacitors and transistors storing electrical charges to represent memory 18

3 states. DRAM chips are small, simple, cheap, easy to make and four time as much information as a static RAM (SRAM) chip of similar complexity. SRAM: SRAM (Static RAM) storage is based on the logic circuit known as flip-flop, which retains the information stored in it as long as there is enough power to run the device. A static RAM chip can store only about one-fourth as much data as a dynamic RAM. Static RAM does not need to be refreshed, which makes it faster than DRAM. It is also more expensive. Q: Define ROM and its types. Ans: ROM: It is a kind of primary memory. ROM (Read Only Memory) is a permanent memory. At the time of making a computer, some programs are stored in ROM. Whenever the computer is switched on these programs are automatically executed. These programs are never removed even when the computer is switched off. It has special programs called Firmware for this purpose stored in it. The user can read the programs or information from this memory but cannot write his own program on it. That is why it is called Read Only Memory (ROM). ROM can be of three types, which are as follows: PROM (Programmable Read Only Memory) User can store a program but once the PROM has been used, user cannot clean it and use it to store something else. It is non-volatile. EPROM (Erasable Programmable Read Only Memory) It provides user both programming and re-programming facilities. EEPROM (Electrically Erasable Programmable Read Only Memory) It is a permanent memory on which user can write and erase his programs. Like EPROM, after erasing data user can reuse it. Q: What is the difference between SIMM and DIMM? Ans: SIMM: SIMM (single in-line memory module) is a module containing one or several Random Access Memory (RAM) chips on a small circuit board with pins that connect to the computer motherboard. SIMMs typically comes with a 32-data bit path to the computer that requires a 72-pin connecter. SIMMs usually comes in memory chip multiples of four megabytes. The memory chips on a SIMM are typically DRAM chips. 19

4 DIMM: A DIMM (dual in-line memory module) is a double SIMM. Like a SIMM, it s a module containing one or several random access memory (RAM) chips on a small circuit board with pins that connect it to the computer motherboard. A DIMM has a 168-pin connector and support 64-bit data transfer. It is considered that future computers will standardize on the DIMM. Q: What do mean by Units of memory and what are the Units of memory? Ans: Units of Memory: Data currently being processed is stored in memory register. Computer memory is an array of storage boxes, each of which is one byte in length. Each byte is the combination of eight (8) small units called bits (binary digit). Each bit is capable to store either 0 or 1 which are used to understand machine language. The smallest unit of memory is bit, but the smallest accessible unit of memory is Byte because we can store a single character of information in a byte not in a bit. A group of four bits is called a nibble but memory of computer is expressed in bytes. Prefix Symbol Power of 10 Power of 2 Equivalent Kilo K Bytes Mega M K-Bytes Giga G M-Bytes Tera T G-Bytes Q: Define the following. 1. Floppy Diskette 2. Hard Disk 3. Compact Disk Ans: Floppy Diskette: It is a small removable, portable storage device. It is readable by a computer with a floppy disk drive. It was a very common and popular storage device. We carried out data in a floppy and used it in any computer having a floppy drive to view. The read/write head in the Floppy Drive reads and writes the data on the floppy. These days floppies come in a standard size of 3.5 inches. The Floppy Disks we commonly used can store 1.44 MB (megabytes) of data. Hard Disk: The main device that the computer uses in order to store more information is the Hard disk or Hard Drive. It has a very large storage capacity. We can read as well as write data on the Hard Disk as many times as we may need. 20

5 A hard disk is a magnetic disk on which we can store computer data. The term hard is used to distinguish it from a soft, or floppy disk. Hard disks hold more data and are faster than floppy disks. Today s computers typically come with a hard disk that contains several billion bytes (gigabytes) of storage. The storage capacity of a Hard disk is always measured in megabyte and gigabytes. One gigabyte contains 1024 MB (megabytes). Nowadays, a normal Hard Disk Drive contains 40 GB (gigabytes) of disk space. Compact Disk: A compact disk commonly known as CD. It is also a portable storage device. It is a circular disk made of a hare plastic material and is coated with a very thin layer of metal. It is designed to store computer data in the form of text and graphics as well as hi-fi sound. It is popular for distribution of large databases, software and especially multimedia applications. Q: Write about magnetic tape. Ans: Magnetic Tape: A magnetic tape is also a storage device from which we can access data serially like an audio cassette from which we can hear the songs in order in which they are stored. When we want to access some particular data from the tap, the device has to scan through all the data we do not need but that data is stored before the required one. The best use of the magnetic tape is for the data that we do not use very often. The recording medium is a plastic tape coated with some magnetic material on one side only and this coated side is used to record data. Two kinds of blank spots, called gaps, are set on the tap. Interblock gap, which separates logical blocks. Interrecord gap, which is wider and separates records. Sir Sadiq s Computer Notes for Class IX. Composed by: Sir Sadiq smsadiqnoori@gmail.com 21