Memory Of Computer | Primary and Secondary Storage

Memory is an area of computer where information is stored temporarily in RAM & permanently in ROM. It is capable of storing the instructions before as well as after processing of inputs. The basic function of these storage devices is to store the data, instructions, the outputs in the computer system so that they can be accessed by the users whenever they want to use them in the future.

Memory Of Computer | Primary and Secondary Storage

Types Of Memory

The computer memory has been categorized into two large categories:

  • Primary Storage
  • Secondary Storage

Primary Storage | Main Memory | Volatile Memory

Primary storage is also known as main memory as they directly stores the data accepted by the input devices before processing. It is also called temporary memory because it temporarily stores data in it & data can be lost if there is any power failure. It is unable to store the data in bulk. It consists of storage locations & each of these locations has a unique number known as Storage Address. Due to these unique storage address, it becomes easy for the system to access directly any particular type of data.

Primary memory <=>Processor

The main memory directly interacts with the processor of the computer.

Other Words For Primary Memory

  • Volatile Memory
  • Main Memory
  • Temporary Memory
  • Internal Memory

Types Of Primary Storage

  • RAM (Random Access Memory)
  • ROM (Read-Only Memory)
  • Cache Memory
  • Virtual Memory

RAM (Random Access Memory)

RAM stores the data entered by the user into the computer & this stored data is accessed randomly that’s why it is named so Random Access Memory. In simple words, you can say that it stores data that is currently using. Computers can easily fetch data from RAM but it will vanish out as the power goes down. RAM is generally used by many devices such as PCs, tablets, servers, smartphones, etc. RAM is available in the computer in the form of chips. It becomes easy to read and write the data (in the RAM) instantly. It is a volatile memory.

 Types Of RAM

SRAM: SRAM stands for Static Random Access Memory. The word static means that it holds the data till the memory is applied to it & it does not need to refresh the data repeatedly. Data is lost in static RAM when power goes down. Hence, it is a volatile memory. It is also called 6T SRAM as it includes 6 transistors to form a single memory cell. As compared to the DRAM it is more costly, uses more power, can grip less data.
DRAM: DRAM stands for Dynamic Random Memory. It requires to refresh the data periodically (after every two milliseconds) as in DRAM it does not matter that power is ON or OFF because it loses stored data in a few milliseconds even the power is ON. It is cost is reasonable and consumes less power.

ROM (Read-Only Memory)

ROM is also called non-volatile memory as it can hold the data without the flow of any electricity. It consists of a tiny chip placed near the CPU on the motherboard. It is a permanent type of storage. It does not lose the stored data even the computer’s power is switched OFF. It is in-built in computer memory. The instructions which are required to start the computer is stored in ROM & this process is known as bootstrap. In ROM the user cannot write the instructions because it is read-only memory. In ROM data does not store & selected randomly as happened in RAM. When we switch on the computer system the instructions has stored in the ROM get loaded and after they executed naturally. This ROM chips can also be seen in many other electronic devices like calculator, washing machines, microwave oven, etc.

Types Of ROM

PROM(Programmable Read-Only Memory): It is also known as User Programmable Read-Only Memory as the instructions are programmed by the use. These instructions can be design & modify only at once by the user as he required. That’s why it is also called One-time programmable non-volatile memory.
EPROM (Erasable Programmable Read-Only Memory): In EPROM the user can design the instructions as well as erase them by using Ultra-Violet Rays (UV-Rays) according to his requirement. User has also the advantage of reprogramming the instructions into it but can not read any information.
EEPROM (Electrically Erasable Programmable Read-Only Memory): In this user according to his requirement can program as well as reprogram the instructions. Instructions are erased electrically (through electrical pulses) in EEPROM. Users can easily erase a small section of the contents of the ROM. EEPROM is quite useful when slight changes are required in the contents.

Cache Memory

Cache is also a volatile memory & hence, data is lost in case of power down. It is a space between the computer’s hard drive & RAM. Browser saves copies in it. It has low capacity. It is a very high-speed memory lies between the main memory & the processor. It is also called Buffers.

As we all know that a program is a set of instructions. So, when you run a program these instructions are supplied by the primary memory to the CPU. At first, the data get loaded into the RAM & after that it is issued to the CPU. CPU is capable of bringing out a massive number of instructions per second but RAM is not able to deliver the data to all the cores of the CPU at the same time. Hence, CPU demands access to a super-fast memory. So, here the cache memory comes in use. Cache memory is the fastest among all the memories. It is also a RAM but it belongs to a special kind of RAM, called as Static RAM. The cache has memory size in the range of kilobytes up to megabytes. The data which is usually required by the CPU is stored in the cache as well as supplied by it. It includes different levels of memory.

Different Levels Of Cache Memory Are

Level 1 Cache (L1 Cache): L1 cache is a slight amount of memory mixed in the CPU itself. All CPU has individual L1 cache. This level can operate at the same speed as the CPU. That’s why it is the fastest among all the levels of the cache. Its memory size is 2KB to 64KB. L1 cache is divided into instruction cache and data cache. Instruction cache deals with the instructions required by the CPU to operate while data cache stores the data on which the operation is to be performed.
Level 2 Cache (L2 Cache): L2  cache may be internal or external to the CPU. It may be separated from all the cores or may be shared by all the cores of the CPU. If it is outside the CPU it is connected with a very high-speed bus with the CPU. Its size is bigger but its speed is slower as compared to the L1 Cache. Its memory size is 256KB to 312KB.
Level 3 Cache (L3 Cache): L3 cache is the largest memory unit but it has the slowest speed among all the levels of the cache. Its memory size is 1MB to 8MB. Not all the processors have this L3 Cache but it is available in some higher processors.

How process Flows In cache?

CPU <=> L1 Cache <=> L2 Cache <=> L3 Cache <=> RAM <=> HDD

If CPU needs some data it will look inside the L1 cache. If the processor will not find the data in the L1 cache then, it will look inside the L2 cache. If it will not find the data in the L2 cache it will look inside the L3 cache. If the data will not find in the L3 cache then, it will look in the RAM. If the data does not found in the RAM then at the end it will look inside the hard disk drive (HDD).

Virtual Memory

RAM is necessary for performing multiprocessing functions at the same time. But when the space in the RAM is not sufficient to store the data as its size decreases when various applications are opened at the same that situation, no other program will run. So, to overcome this problem virtual memory is required by the system to perform the alternative tasks of the RAM. Virtual memory provides another RAM which is quite different from the physical RAM. Physical RAM is available in the form of a chip & the size of the RAM is limited while virtual memory is in the form of software that takes space of all the disks in the computer.

Secondary Storage/Auxiliary Storage/Non-volatile Memory

Secondary memory is also called non-volatile memory as the data stored in the secondary memory is not lost even the power of the computer is switched OFF. Auxiliary memory is permanent as it stores the permanently till the user does not delete or modify it. Users can access the data in the future whenever he wants to use or reshape it.

Other Words For Secondary Storage are:

  • External Memory
  • Secondary Memory
  • Non-volatile Memory
  • Auxiliary Memory

Types Of Secondary Storage

  • Magnetic Storage
  • Optical Storage
  • Solid State Storage

Magnetic Storage

It is the storage of data in the magnetic medium. This magnetic medium uses different arrangements of magnetization to store data in the digital form. They are usually used to store large amounts of data. Magnetic is subsisted of:

(1) Magnetic Tape: It works on the sequential access method which means that you can access/read the data in the same sequence in which you have stored the data into it. It is made up of a plastic material called Mylar. Magnetic tapes can be easily carried out from one place to another. Data is stored in them in the form of binary digits. Data can be deleted from the tape and current data can be stored into it. They are used in the form of cassettes and cartridges. Cassettes are used to store the data in the form of audio while cartridges are used to store the data in the form of audio, video.

(2) Magnetic Disk: It works on the direct access method in which you can easily access any data directly that you want to use. There is no need to access the data in sequence to approach the desired data. It is also made up of plastic material i.e., Mylar. Any portion of the data can be accessed by the user directly. It consists of sectors and tracks. Tracks are the coordinated circles & sectors are the portions generated by splitting the disks into the number of sections.

Types Of Magnetic Disks:

Floppy Disk/Removable disk: Floppy disk is a storage medium, collection of a disk of delicate & soft magnetic storage medium. It is used to store data permanently on the floppy disk & it has low storage capacity. It is wrapped in a rectangular plastic carrier. It consists of concentric circular tracks and these tracks are further divided into sectors. Data is stored in these tracks. You can reuse the floppy disk & you can add new data into it after eliminating the earlier data. It is sensitive to external environmental factors such as dust, temperature, moisture, etc. It is also known by some other names like:

  • 3.5″ Drive,
  • 5.25″ Drive,
  • Disk Drive,
  • Diskette Drive,
  • Removable Disk,
  • Floppy Diskette,
  • Floppy Disk Drive.
Hard Disk/Fixed disk: Hard disk also has a magnetization storage medium. It is used to record and store the data. Information is still maintained even you turn off your computer. It has high storage capacity as compared to the floppy disk. It consists of rotating disks called platters & covered with, magnetic material. It is also known by names such as:

  • Fixed Disk,
  • Hard Drive,
  • Non-removable Disk.

Optical Storage

In optical storage, data is stored on the optical medium by using a beam of laser light. It uses laser light to store & retrieve the information. The devices used optical technology to store data is called optical storage devices. It is non-volatile as the data is retained even the system is switched off. It provides high storage capacity at low cost.

Types Of Optical Disk

(1) CD-ROM: It stands for Compact Disk Read-Only Memory. It is the storage medium in which various types of data can be stored in digital form like images, video, playback audio, etc. It has a storage capacity of 630 MB. It uses the method of One Time Write which means that once you have stored data into it you cannot delete it. In simple words you can say that it is not reusable storage device. You can write the data into it only at once. You can read the CD-ROM in CD-Player, CD-ROM Drive, CD Drive, etc.

CD-ROM is further organized as:

  • WORM Disk: WORM disk states that Write once read for many. It means it is the storage device in which you can write the data only at once but can read the data many times whenever you want to read it. Suppose you have stored  100 MB data in a WORM disk then the remaining space will be waste as you once write data into it.
  • CD-Recordable (CD-R): CD-R is usually used for recording audios. It is used to write data only for once but the data stored into it can be read multiple times. You can make use of every MB of disk. Suppose you have recorded 200MB data in the disk & after that the remaining space 500MB can be recorded next.
  • CD-Rewritable (CD-RW): In CD-RW users can write the data multiple times. It is a reusable storage device in which you can add new data after erasing the previous one. It is expensive than the other CD’s.

(2) DVD (Digital Versatile/Video Disk)/DVD-ROM

It is generally used for storing large applications. It is just similar to a CD-ROM but it has high storage capacity. It can store data minimum of 4.38GB and maximum of 17GB. It stores data permanently which cannot be modified or erased.

Solid State Storage/drive (SSS/ SSD)

Solid State Storage is a non-volatile memory that stores digital data by using electronic circuits (integrated circuit). This device is working stores data without any moving mechanical parts & this type of storage is also known as flash memory. This memory is permanent and does not erase data when the power is switched off.

 Types Of Solid State Storage

Flash Drive: Flash drive is a storage device that connects to the computer and other devices to store data into it. It comes with different storage capacities such as 512MB, 1GB, 2GB, 4GB, 8GB, 16GB, 32GB, etc. It is portable & removable storage device. A pen drive makes easy for the users to transfer the data from one computer to another. USB ports are available in the computer to insert flash drive into it. It is also non-volatile. It is usually referred to as pen drives, thumb drives or jump drives.
Memory Card (SD/MMC): It is also known as flashcards. It is an electronic flash storage device used to store data in digital format. The most popular type of memory cards are Secure Digital (SD) and Multimedia Memory Card (MMC). Its storage capacity ranges from 64MB to 8GB. They are usually used in devices like mobile phones, laptops, digital cameras, etc.



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