COMPUTER MEMORY (IMPORTANT NOTES)

The capability of computer to remember our data is called as memory. In computer it is implemented through electronic circuit. Computer memory is a physical device which is capable of storing information temporarily or permanently. Memory can be classified into two categories ----

1. Primary Memory ( Temporary Memory)
2. Secondary Memory ( Permanent Memory) 

1. Primary Memory :- Primary Memory is also called internal, main or central memory. All data and instructions just of all process into the main memory or primary memory. It store program and data while computer is running. Primary Memory is classified into two categories ------

• RAM (Random Access Memory)
• ROM (Read Only Memory)

• RAM :- It is read and write memory, so user can either read or write from it. It is volatile in nature, means when the computer is switched off, all the information stored on it, will be erased.

Types of RAM --------

➝ SRAM

➝ DRAM

SRAM is stand for Static RAM whereas DRAM is stand for Dynamic RAM. Static RAM retain stored information as long as the power supply is on, but the Dynamic RAM loses its stored information in a very short time even when the power supply in on.

Dynamic RAM are cheaper and have moderate speed. Static RAM are costlier and consume more power. They do not need refreshing circuitry and have higher speed than Dynamic RAM.

• ROM :- ROM is a permanent type of memory, it contains our data even when the power supply is switched off because it is non-volatile in nature. However the user cannot write into a ROM. 

Types of ROM ------

➝ PROM (Programmable ROM) 

➝ EPROM (Erasable Programmable ROM)

✳️ Electrically EPROM (EEPROM)

✳️ Ultraviolet EPROM (UVEPROM)

      2. Secondary Memory :- You cannot store data in the main memory of a PC permanently, because it is very expensive and its contents are erased when the computer is turned off. It order to preserve or save the work which you have done on your computer (permanently fro future use) before you shut it off, you need secondary storage medium. Secondary Memory is also known as Auxiliary Memory.

Types of Secondary Memory -------

➝ Magnetic Disk

  

     ✳️ Floppy Disk :- It is also known as disk or diskette,a floppy disk is a removable storage disk used for storing data, it is floppy disk because the round film inside the disks plastic shell is flexible.

Floppies are available in 3.5''(inch) with a capacity 1.44 MB or 2.88 MB and 5.22''(inch) size with a capacity 160 KB, 360 KB, or 1.2 MB.

      ✳️Hard Disk :- A Hard Disk is a device used for mass storage of data. The data stored on the hard disk can be retrieved at very fast speed. unlike floppies, CDs, etc cannot easily remove a hard disk from a PC.

➝ Optic Disc 

      ✳️ CD ROM :- It is an optical read only memory. The disc is made up of polycarbonate. CD ROM provide random access data retrieval and the disc have a self life of more than 40 years. CD ROM can store about 700 MB.

      ✳️ DVD (Digital Versatile Disc) :- DVD disc provide more more storage capacity than a CD ROM disc. The disc used with DVD drives are of same diameter and thickness as traditional CDs. Like CD and DVD disc can tolerate dust and fingre prints. DVD ROM of capacity ranging from 4.7 GB to 50 GB.

➝ Flash Memory 

      ✳️ Pen Drive :- A Pen Drive or USB flash drive is a portable data storage device. Pen Drive have replace the floppy disk and have become the most popular data storage devices among consumers. To access the data stored in a pen drive, the drive must be connected to a computer through USB host controller. Pen Drive are available in many capacities like 2 GB, 4 GB, 8 GB, 16 GB and so on.

Cache/Cash Memory :- Cache Memory is placed in between the CPU and the main memory. It is faster than main memory. Cache memory provides faster data storage  and access by storing data routinely accessed by the processor. Thus, when our processor requests data that already has an instance in the cache memory, it does not used to go to the memory or the hard disk to fetch the data. There are three labels of cache ------

     ✳️ Label 1 Cache (L1)

     ✳️ Label 2 Cache (L2)

     ✳️ Label 3 cache (L3)

Computer Memory Units ---

1 or 0                    ￫ 1 Bite

4 Bits                    ￫ 1 Nibble or 1/2 Byte

8 Bits                    ￫ 1 Byte

1024 Bytes           ￫ 1 Kilobyte

1024 Kilobytes    ￫ 1 Megabyte

1024 Megabytes   ￫ 1 Gigabyte

1024 Gigabytes    ￫ 1 Terabyte

1024 Terabytes     ￫ 1 Petabyte

1024 Petabytes     ￫ 1 Exabytes

1024 Exabytes      ￫ 1 Zettabyte

1024 Zettabytes    ￫1 Yottabyte

1024 Yottabye      ￫ 1 Brontobyte

1024 Brontobyte  ￫ 1Geopbyte