Computer storage has components that store computer data. The different storage types in the storage hierarchy are as follows: Primary Storage This is also known as the main memory and is the memory directly accessible by the CPU. All the instructions are executed in the main memory by CPU and the data required by these instructions is also stored in main memory. Main memory primarily consists of the RAM which is volatile in nature. It is also quite small compared to secondary memory and expensive as well. Secondary Storage Secondary or external storage is not directly accessible by the ... Read More

Computer storage contains many components that are used to store computer data. Some information about the various storage devices is given below.Computer Storage DefinitionsThe computer storage devices include Primary and Secondary Storage devices. These are explained in detail as follows −Primary Storage DevicesPrimary storage is also known as the main memory and is the memory directly accessible by the CPU. Some primary storage devices are −ROMROM is read only memory. This memory cannot be changed, it can only be read as required. Since ROM is unchangeable memory, it is used by data and programs that are frequently required and seldom ... Read More

The computer system is a combination of many parts such as peripheral devices, secondary memory, CPU etc. This can be explained more clearly using a diagram.The salient points about the above figure displaying Computer System Organisation is −The I/O devices and the CPU both execute concurrently. Some of the processes are scheduled for the CPU and at the same time, some are undergoing input/output operations.There are multiple device controllers, each in charge of a particular device such as keyboard, mouse, printer etc.There is buffer available for each of the devices. The input and output data can be stored in these ... Read More

An operating system is a construct that allows the user application programs to interact with the system hardware. Operating system by itself does not provide any function but it provides an atmosphere in which different applications and programs can do useful work.The place of an operating system in a computer can be demonstrated aptly using the following diagram:As can be seen from the above diagram, the computer system is divided into four components namely, hardware, operating system, application programs and users.The operating system coordinates between the hardware and the application programs. It makes sure that adequate hardware resources are distributed ... Read More

SQL (Structured Query Language) is a specialized programming language which is standardized to be used for managing relational databases and performing various operations on the data. There are various uses of SQL which includes modifying database table and index structures; adding, updating and deleting rows of data; and retrieving various subsets of information from a database for transaction processing and analytics applications. There are specialized queries and operations which operates in the form of commands and commonly known as SQL statements like select, add, insert, update, delete, create, alter and truncate.SQL became standard programming language for relational databases after they ... Read More

A hierarchical model represents the data in a tree-like structure in which there is a single parent for each record. To maintain order there is a sort field which keeps sibling nodes into a recorded manner. These types of models are designed basically for the early mainframe database management systems, like the Information Management System (IMS) by IBM.This model structure allows the one-to-one and a one-to-many relationship between two/ various types of data. This structure is very helpful in describing many relationships in the real world; table of contents, any nested and sorted information.The hierarchical structure is used as the ... Read More

In a "product sales" database, a product may have optional supplementary information such as image, more description and comment. Keeping them inside the Products table results in many empty spaces (in those records without these optional data). Furthermore, these large data may degrade the performance of the database.Instead, we can create another table (say ProductDetails, ProductLines or ProductExtras) to store the optional data. A record will only be created for those products with optional data. The two tables, Products and ProductDetails, exhibit a one-to-one relationship. That is, for every row in the parent table, there is at most one row ... Read More

In a "product sales" database, a customer's order may contain one or more products; and a product can appear in many orders. In a "bookstore" database, a book is written by one or more authors; while an author may write zero or more books. This kind of relationship is known as many-to-many.Let's illustrate with a "product sales" database. We begin with two tables: Products and Orders. The table products contain information about the products (such as name, description and quantityInStock) with productID as its primary key. The table orders contain customer's orders (customerID, dateOrdered, dateRequired and status). Again, we cannot ... Read More

In a "class roster" database, a teacher may teach zero or more classes, while a class is taught by one (and only one) teacher. In a "company" database, a manager manages zero or more employees, while an employee is managed by one (and only one) manager. In a "product sales" database, a customer may place many orders; while an order is placed by one particular customer. This kind of relationship is known as one-to-many.The one-to-many relationship cannot be represented in a single table. For example, in a "class roster" database, we may begin with a table called Teachers, which stores ... Read More

Relational database design (RDD) models’ information and data into a set of tables with rows and columns. Each row of a relation/table represents a record, and each column represents an attribute of data. The Structured Query Language (SQL) is used to manipulate relational databases. The design of a relational database is composed of four stages, where the data are modeled into a set of related tables. The stages are −Define relations/attributesDefine primary keysDefine relationshipsNormalizationRelational databases differ from other databases in their approach to organizing data and performing transactions. In an RDD, the data are organized into tables and all types ... Read More