Computer Storage Structure
The main use of computers is to store and retrieve data. The data are generally stored in memory and memory is divided into two types,
1. Primary memory
2. Secondary Memory
1) PRIMARY MEMORY
The memory that communicates directly with the CPU is called Main or Primary memory It is actually a group of cells, known as memory cells having two stable states either 0’s or l’s. Each memory cell can store one bit at a time. It is used to store programs and data during the processor execution. It is a volatile type of memory.
Some of the commonly used Primary Computer Storage devices are as follows,
- ROM
- RAM
- Cache Memory
ROM
This memory never changes, RAM is known as Read-Only Memory. It can be only read as need. ROM is unchangeable memory, Rom uses data (Information) Or Programs that required.
RAM
This is also known as volatile. RAM is Random Access Memory, It is also an expensive Component of a Computer. Its stores data temporarily, it helps to computer to do the process.
CACHE MEMORY
Cache Memory is used to store information(data) and instructions, for Example, Cache Memory is used to store cookies browser passwords and etc., Cache Memory is regularly needed by the CPU to perform faster, This is a very mini memory and very fast.
2) SECONDARY MEMORY
The primary memory storage device is volatile memory expensive and has limited capacity. To overcome the above problems, secondary Computer storage is used. The secondary type of memory is also called auxiliary memory or backup storage etc. This type of memory is used for supporting the actual main memory. As storing currently unused data may waste a lot of memory space in primary storage, therefore such data are stored on secondary Computer Storage devices, which can be used if required later. These types of storage provide a lot of Computer storage space and they are cheaper compared to primary memory but one can not execute the program in the secondary memory.
Some of the commonly used secondary Computer Storage devices are as follows,
- Magnetic Disks
- Magnetic Tape
- Optical Disks
- Floppy Disk
- Memory Card
- Flash Drive
The main parameters to evaluate disk are as follows.
- Number of tracks
- Number of sectors
- Storage capacity
- Price
- Access technique (Sequential/Random etc)
- External/ Internal
MAGNETIC DISK (HARD DISK)
It is coated with ferromagnetic material. They could be used as an input or output device on the computer system. It is the most popular medium for the Direct Access Computer Storage device Data is recorded and can be accessed in sequence or randomly. They are available in different sizes and capacities. They can be portable and permanently mounted in the storage device called disk drives.
The most commonly used magnetic disk devices are floppy disks and hard disks The working of the magnetic disk is similar to that of a gramophone record. They use different techniques for data accessing and also differ in the data transfer rate. In magnetic disk, Read/Write heads are small electromagnets that are capable to read, write or erase the data stored as magnetic dots. These disks are capable to rotate at a very high speed of about 1800-3600 revolutions per minute.
MAGNETIC TAPE
Magnetic tape works like a cassette tape. The tape used for storage is a 125 ta 25 mm wide plastic film and is 500 to 1200 meters long. It is coated with a magnetizable material. The spool containing the tape is made to run on the deck connected to the processor The information is then fed or read from the tape through the processor. The data stored on these tapes could be erased and written many times.
It provides the serial or sequential type of access. It is frequently used to transport data program from one computer site to another
OPTICAL DISK OR LASER DISK (CD- ROM)
In this type of Computer storage device, thin metal is coated which is a highly reflective material and due to which laser beam technology is used to read and write data on the disk. it is a part of Computer Storage. The recording is done by focusing a laser beam on the surface of the spinning disk. The laser beam is turned on and off to build some specific codes and hence tiny holes are made into the metal coating of the disk.
When a laser beam of low intensity is focused on the disk, the metal surface reflects that laser back and a small or negligible amount of laser is reflected back, hence recognizing this data can be decoded in the form of ON/OFF reflections and converted into the electronic signals. The recording technique of this type of device is complex
Optical disks are mounted on an Optical disk drive which contains a motor to rotate the disk and the most common disk drives are CD-ROM (Compact Disk Read Only Memory DVD (Digital Versatile Disk, formally Digital Video Disk), etc.
FLOPPY DISK
This disk is the most popular way of storage of data for micro and mini-computers. It consists of flexible plastic which is coated with magnetic oxide, enclosed within a jacket to protect it from contamination. The data is read from the aperture in the jacket when mounted on the drive. Data can be easily read and written onto the floppy disk. They are typically 3.5 25, or 8 inches in diameter. They come in either single or double density versions. They are of four types,
- Single-sided single density
- Single-sided double-density
- Double-sided single density
- Double-sided double-density
The access mechanism in the floppy disk is fast, reliable, and could be used many times These media are more popular because of their portability when compared to other Computer Storage devices but should be handled carefully. The storage capacity floppy disk is quite small (1.44 MB). It also takes high access time and a low transfer rate of data.
MEMORY CARD
The Memory Card is a type of permanent Computer storage device or secondary Computer storage device. this device having similar functionality to Flash Drive and It is a plug-and-play device. you can store data permanently, but it has a risk to corrupt data after long use. A memory card is available in so many Sizes like 8MB, 16Mb, 128MB, 512MB and etc., the Minimum size of a Memory Card is 8 MB and the Maximum size is 1 TB.
FLASH DRIVE
Flash Drive is also known as Pen Drive. this the best portable device which, unlike an Optical Drive or its does not have any moving parts. other devices connect via a built-in USB Type-A or USB Type-B plug. computers and range in sizes from 2GB to 1 TB. Flash drive is a plug-and-play device.
Comparison between Hard Disk and Floppy Disk
Comparison between Primary Storage and Secondary Storage
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