Computer Science
Units of Data Storage
Units of data storage refer to the different ways in which digital information is measured and stored. The most common units of data storage include bits, bytes, kilobytes, megabytes, gigabytes, terabytes, and petabytes. These units are used to quantify the amount of data that can be stored on a computer or other digital device.
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5 Key excerpts on "Units of Data Storage"
eBook - PDF- Hossein Bidgoli(Author)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
2-3c Storage and Retrieval Storage means saving data in computer memory, and retrieval means accessing data from memory. Computers can store vast quantities of data and locate a specific item quickly, which makes knowledge workers more efficient in performing their jobs. In computers, data is stored in bits. A bit is a single value of 0 or 1, and 8 bits equal 1 byte. A byte is the size of a character. For example, the word computer consists of 8 characters or 8 bytes (64 bits). Table 2.3 shows stor- age measurements. Every character, number, or symbol on the keyboard is represented as a binary number in computer memory. A binary system consists of 0s and 1s, with a 1 representing “on” and a 0 representing “off,” similar to a light switch. Computers and communication systems use data codes to represent and transfer data between comput- ers and network systems. The most common data code for text files, PC applications, and the Internet is the American Standard Code for Information Interchange (ASCII), developed by the American National Standards Institute. In an ASCII file, each alphabetic, numeric, or special character is represented with a 7-bit binary num- ber (a string of 0s or 1s). Up to 128 (2 ) 7 characters can be defined. There are two additional data codes used by many operating systems: Unicode and Extended ASCII. Unicode is capable of representing 256 (2 ) 8 characters, and Extended ASCII is an 8-bit code that also allows representation of 256 characters. Before the ASCII format, IBM’s Extended Binary Coded Decimal Interchange Code (EBCDIC) was popular. In an EBCDIC file, each alphabetic, numeric, or special character is represented with an 8-bit binary number. The “A Supercomputer in Your Pocket” box high- lights the power of smartphones that are faster than a supercomputer of a few years ago. 2-4 COMPUTER OPERATIONS Computers can perform three basic tasks: arithmetic operations, logical operations, and storage and retrieval operations.
eBook - PDF- M Smit R Jonker(Author)
- 2017(Publication Date)
- Macmillan(Publisher)
Each character or number that makes up the source code is assigned a unique ‘bit pattern’. The computer stores all data electronically using binary digits . A bi nary digi t is known for short as a bit . A bit can be in one of two states: ‘on’ or ‘off’, equivalent to 1 and 2. One bit can only be used to represent two different values, 0 and 1. However, by grouping bits together we can store more values, for example: • 2 bits (2 2 ) can represent 4 different values: 00, 01, 10 and 11. • 3 bits (2 3 ) can represent 8 different values: 000, 001, 010, 100, 011, 101, 110 and 111, and so on. A data unit that consists of 8 bits (2 8 ) is known as a byte and it can represent 256 values. Other terms used for data units are as follows: • A nybble is equal to 4 bits. • A halfword is equal to 16 bits or 2 bytes. • A word is equal to 32 bits or 4 bytes. • A doubleword is equal to 64 bits or 8 bytes. Programming languages may specify data sizes in different terms, for example Java defines four sizes: byte = 8 bits; short = 16 bits; int = 32 bits and long = 64 bits. 82 Module 10 10.1.2 How data is stored in memory Computer memory plays an important role in saving and retrieving data. In a computer, programs and data are stored on a hard disk drive, also known as secondary memory. Whenever you access a program, the instructions that have to be executed are copied to the computer’s primary memory, also called random access memory (RAM), from where it can be accessed quickly by the CPU. Apart from hard disk drives and RAM, there are also other types of memory that can be used to store data and programs. The different methods of storing data are shown in Figure 10.1.
eBook - PDF- Greg Tomsho(Author)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
An Overview of Computer Storage One of the main reasons people use computers is to create, receive, and download files and documents of every type. Everything is stored on digital media now—documents, email, music, photographs, videos—and this trend is continuing. In addition, people want instant access to whatever they store. Just about every large Internet company has its own version of cloud storage, including Dropbox, iCloud, Google Drive, and Microsoft’s OneDrive. Dozens of cloud storage services are competing to store your files, and although these services are convenient and seemingly work by magic, they all start with a computer and storage devices. The following sections cover some basics of computer storage: what it is, why you need it, and the common methods for accessing storage. What is Storage? Generally speaking, storage is any digital medium that data can be written to and later retrieved. Technically, this definition includes random access memory (RAM), but the term computer storage generally means long-term storage in which data is maintained without a power source; for example, RAM only holds data when it has electrical power, and is referred to as volatile storage. Long-term storage, such as hard disks and flash drives, maintains data when the power is turned off and is referred to as non-volatile storage.
eBook - PDF- Paul Murrell(Author)
- 2009(Publication Date)
- Chapman and Hall/CRC(Publisher)
The first things we need to establish are some fundamental ideas about computer memory. 5.2.1 Computer memory The most fundamental unit of computer memory is the bit . A bit can be a tiny magnetic region on a hard disk, a tiny dent in the reflective material on a CD or DVD, or a tiny transistor on a memory stick. Whatever the physical implementation, the important thing to know about a bit is that, like a switch, it can only take one of two values: it is either “on” or “off”. 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 byte bit word A collection of 8 bits is called a byte and (on the majority of computers today) a collection of 4 bytes, or 32 bits, is called a word . 5.2.2 Files and formats A file is simply a block of computer memory. A file can be as small as just a few bytes or it can be several gigabytes in size (thousands of millions of bytes). A file format is a way of interpreting the bytes in a file. For example, in the simplest case, a plain text format means that each byte is used to represent a single character. In order to visualize the idea of file formats, we will display a block of memory in the format shown below. This example shows the first 24 bytes from the PDF file for this book. 72 Introduction to Data Technologies 0 : 00100101 01010000 01000100 01000110 | %PDF 4 : 00101101 00110001 00101110 00110100 | -1.4 8 : 00001010 00110101 00100000 00110000 | .5 0 12 : 00100000 01101111 01100010 01101010 | obj 16 : 00001010 00111100 00111100 00100000 | .<< 20 : 00101111 01010011 00100000 00101111 | /S / This display has three columns. On the left is a byte offset that indicates the memory location within the file for each row. The middle column displays the raw memory contents of the file, which is just a series of 0 ’s and 1 ’s. The right hand column displays an interpretation of the bytes. This display is split across several rows just so that it will fit onto the printed page.
- Adele Kuzmiakova(Author)
- 2020(Publication Date)
- Arcler Press(Publisher)
• Storage unit: Storage devices are part of the computer hardware to store and remember data. There are many types of storage device: • Hard disk drive – these are magnetic storage devices that are not volatile and are capable of storing a large amount of data. They have an electromagnet in the read and write head that charges the surface of the disk with either a positive or negative charge. This is how the binary numbers one or zero are represented. The head is then able to detect the magnetic charges that are left on the surface of the disc and this is how the data on the disk is interpreted. The surface of the disc is divided into two parts: concentric circles and sixes. This division helps to provide specific locations which Introduction to Computer Science and Technology 46 can help in remembering where the data was saved. Coordination of the rotating disk and swinging actuator arm are carefully done by the circuit board which gives the opportunity to the read and write head to find access to the specific locations in a fast manner. Hard disk drive capacities on measured in Terabytes. They can be installed into the computer or bought in format that is portable. One of the disadvantages of hard disk drives is that they can break and wear out easily due to the moving parts. • Solid-state drive – these devices are not volatile and are also able to hold a large amount of data. They use millions of transistors that have been wired in a series on its circuit board. This is called NAND flash memory. This means that they do not have any mechanical moving pads and that can be instantaneous access to the data. Solid-state drives are able to perform much quicker than the normal hard disk drives but they are also quite expensive. The capacities of solid-state drives are measured in gigabytes. Due to their expense, one can compromise by using two disc drives inside one computer.
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