In this article, we will review the capabilities of the Rufus program for creating ...
Information carriers (floppy disks, hard disks, CD-ROM disks, magneto-optical disks, etc.) and their main characteristics.
External (long-term) memory is a place for long-term storage of data (programs, calculation results, texts, etc.) that are not currently used in the computer's RAM. External memory, unlike operational memory, is non-volatile. External memory media, in addition, provide data transportation in cases where computers are not networked (local or global).
To work with external memory, you must have a drive (a device that provides recording and (or) reading information) and a storage device - a carrier.
The main types of drives:
floppy disk drives (FPHD);
hard disk drives (HDD);
magnetic tape drives (NML);
drives CD-ROM, CD-RW, DVD.
They correspond to the main types of media:
floppy disks (Floppy Disk) (3.5'' diameter and 1.44 MB capacity; 5.25'' diameter and 1.2 MB capacity 5.25'', also discontinued)), disks for removable media;
hard magnetic disks (Hard Disk);
cassettes for streamers and other NML;
CD-ROMs, CD-Rs, CD-RWs, DVDs.
Memory devices are usually divided into types and categories in connection with their principles of operation, operational, technical, physical, software and other characteristics. So, for example, according to the principles of functioning, the following types of devices are distinguished: electronic, magnetic, optical and mixed - magneto-optical. Each type of device is organized on the basis of the appropriate technology for storing/reproducing/recording digital information. Therefore, in connection with the type and technical performance of the information carrier, there are: electronic, disk and tape devices.
The main characteristics of drives and media:
information capacity;
speed of information exchange;
reliability of information storage;
price.
Let us dwell in more detail on the consideration of the above drives and media.
The principle of operation of magnetic storage devices is based on methods of storing information using the magnetic properties of materials. As a rule, magnetic storage devices consist of the actual information reading / writing devices and a magnetic medium, on which the recording is directly carried out and from which information is read. Magnetic storage devices are usually divided into types in connection with the performance, physical and technical characteristics of the information carrier, etc. The most commonly distinguished are: disk and tape devices. The general technology of magnetic storage devices is to magnetize sections of the carrier with an alternating magnetic field and read information encoded as regions of variable magnetization. Disk carriers, as a rule, are magnetized along concentric fields - tracks located along the entire plane of a discoidal rotating carrier. Recording is done in digital code. Magnetization is achieved by creating an alternating magnetic field using the read/write heads. The heads are two or more magnetic controlled circuits with cores, the windings of which are supplied with alternating voltage. A change in the voltage value causes a change in the direction of the lines of magnetic induction of the magnetic field and, when the carrier is magnetized, means a change in the value of the information bit from 1 to 0 or from 0 to 1.
Disk devices are divided into flexible (Floppy Disk) and hard (Hard Disk) drives and media. The main property of disk magnetic devices is the recording of information on a carrier on concentric closed tracks using physical and logical digital encoding of information. The flat disc media rotates during the read/write process, which ensures the maintenance of the entire concentric track, reading and writing is carried out using magnetic read/write heads that are positioned along the radius of the media from one track to another.
For the operating system, data on disks is organized into tracks and sectors. Tracks (40 or 80) are narrow concentric rings on the disc. Each track is divided into sections called sectors. When reading or writing, the device always reads or writes an integer number of sectors, regardless of the amount of information requested. The sector size on a floppy disk is 512 bytes. The cylinder is the total number of tracks from which information can be read without moving the heads. Because a floppy disk has only two sides, and a floppy disk drive has only two heads, there are two tracks per cylinder in a floppy disk. A hard drive can have many platters, each with two (or more) heads, so there are many tracks per cylinder. A cluster (or data allocation cell) is the smallest disk area that the operating system uses when writing a file. Usually a cluster is one or more sectors.
The floppy disk must be formatted before use. its logical and physical structure must be created.
Diskettes require careful handling. They may be damaged if
touch the recording surface;
write on the floppy disk label with a pencil or ballpoint pen;
bend a diskette;
overheat the floppy disk (leave it in the sun or near the radiator);
expose the disk to magnetic fields.
Hard disk drives combine media(s) and a read/write device in one package, as well as, often, an interface part called a hard disk controller. A typical design of a hard disk is the execution in the form of a single device - a chamber, inside which there is one or more disk media placed on one axis, and a block of read / write heads with their common drive mechanism. Usually, next to the chamber of media and heads are circuits for controlling heads, disks and, often, an interface part and (or) a controller. The disk device interface itself is located on the interface card of the device, and the controller with its interface is located on the device itself. The drive circuits are connected to the interface adapter using a set of cables.
The principle of functioning of hard disks is similar to this principle for the GMD.
The main physical and logical parameters of the railway.
Disc diameter. The most common drives with disk diameters are 2.2, 2.3, 3.14 and 5.25 inches.
Number of surfaces - determines the number of physical disks strung on the axis.
Number of cylinders - determines how many tracks will be located on one surface.
Number of sectors - the total number of sectors on all tracks of all surfaces of the drive.
The number of sectors per track is the total number of sectors per track. For modern drives, the indicator is conditional, because. they have an unequal number of sectors on external and internal tracks, hidden from the system and user by the device interface.
The transition time from one track to another is usually 3.5 to 5 milliseconds, and the fastest models can be from 0.6 to 1 millisecond. This indicator is one of the determinants of the speed of the drive, because. it is the transition from track to track that is the longest process in a series of random read / write processes on a disk device.
Setup time or seek time - the time taken by the device to move the read / write heads to the desired cylinder from an arbitrary position.
The data rate, also called bandwidth, determines the speed at which data is read from or written to the disk after the heads are in position. It is measured in megabytes per second (MBps) or megabits per second (Mbps) and is a characteristic of the controller and interface.
Currently, hard disks with a capacity of 10 GB to 80 GB are mainly used. The most popular are disks with a capacity of 20, 30, 40 GB.
In addition to NGMD and NGMD, removable media are often used. A fairly popular drive is Zip. It is available as built-in or stand-alone units connected to the parallel port. These drives can store 100 and 250 MB of data on 3.5" floppy cartridges, provide access times of 29 ms, and transfer rates up to 1 MB/s. If a device connects to the system through a parallel port, the data rate is limited by the parallel port rate.
A type of removable hard drive is the Jaz drive. The capacity of the used cartridge is 1 or 2 GB. The disadvantage is the high cost of the cartridge. The main application is data backup.
In magnetic tape drives (most often streamers act as such devices), recording is done on mini-cassettes. The capacity of such cassettes is from 40 MB to 13 GB, the data transfer rate is from 2 to 9 MB per minute, the tape length is from 63.5 to 230 m, the number of tracks is from 20 to 144.
CD-ROM is a read-only optical storage medium that can store up to 650 MB of data. Accessing data on a CD-ROM is faster than data on floppy disks, but slower than on hard drives.
A CD with a diameter of 120 mm (about 4.75'') is made of polymer and covered with a metal film. Information is read from this metal film, which is covered with a polymer that protects data from damage. CD-ROM is a one-sided storage medium.
Information is read from the disk by registering changes in the intensity of the low-power laser radiation reflected from the aluminum layer. The receiver or photosensor determines whether the beam is reflected from a smooth surface, scattered or absorbed. Scattering or absorption of the beam occurs in places where indentations were made during the recording process. The photo sensor senses the scattered beam, and this information is fed to a microprocessor in the form of electrical signals, which converts these signals into binary data or sound.
The speed of reading information from a CD-ROM is compared with the speed of reading information from a music disc (150 Kb/s), which is taken as one. To date, the most common are 52x-speed CD-ROM drives (reading speed 7500 Kb / s).
CD-R (CD-Recordable) drives allow you to burn your own CDs.
More popular are CD-RW drives, which allow you to write and rewrite CD-RW discs, write CD-R discs, read CD-ROM discs, i.e. are, in a certain sense, universal.
The abbreviation DVD stands for Digital Versatile Disk, i.e. universal digital disk. Having the same dimensions as a conventional CD and a very similar principle of operation, it holds an extremely large amount of information - from 4.7 to 17 GB. Perhaps it is because of the large capacity that it is called universal. True, today the DVD disc is actually used only in two areas: for storing video films (DVD-Video or simply DVD) and extra-large databases (DVD-ROM, DVD-R).
The variation in capacities occurs as follows: unlike CD-ROMs, DVDs are recorded on both sides. Moreover, one or two layers of information can be applied on each side. Thus, single-sided single-layer discs have a capacity of 4.7 GB (they are often called DVD-5, i.e. discs with a capacity of about 5 GB), double-sided single-layer discs - 9.4 GB (DVD-10), single-sided double-layer discs - 8.5 GB (DVD-9), and double-sided double-layer - 17 GB (DVD-18). Depending on the amount of data that needs to be stored, the type of DVD disc is selected. When it comes to films, double-sided discs often store two versions of the same picture - one widescreen, the second in the classic television format.
Thus, here is an overview of the main external memory devices, indicating their characteristics. 
... ; end; To determine the height of a row, use the following statement: height:=E.ActiveWorkbook.Sheets.Item.Rows.RowHeight; Task №5 "Excel Spreadsheet Processor" Working with functions in EXEL. Working with files. Working with Functions Prepare a spreadsheet to calculate your weekly public transport spending: Create a spreadsheet using the template. For this: In...
Exe). It is included with MS-DOS and also comes with almost all CD-ROM drives. Device and principle of operation As you know, most drives are external and built-in. CD drives are no exception in this sense. Most CD-ROM drives currently on the market are built-in. External storage is usually...
To store binary numbers in a computer, a device is used, which is commonly called a memory cell. Cells are formed from several bits, just as binary numbers are formed from binary digits. And the entire memory of a computer can be imagined as an automatic storage chamber, consisting of a large number of individual cells, in each of which you can put, write down some binary number. ...
At the same time, information is understood as various information about certain natural phenomena, social events or processes occurring in technical devices. 1. WHAT IS A COMPUTER? What is a personal computer? If you describe it externally, then it is “a small box lying (desktop) or standing (mini-tower) on the table, less often - a box about a meter high (...
By studying this topic, you will learn:
What is computer memory and how does it compare with human memory;
- what are the characteristics of the memory;
- why computer memory is divided into internal and external;
- what is the structure and features of internal memory;
- what are the most common types of external computer memory and what is their purpose.
Purpose and main characteristics of memory
During the operation of a computer program, the initial data, as well as intermediate and final results, must be stored somewhere and be able to access them. To do this, the computer has various storage devices, which are called memory. The information stored in the memory device is various symbols (numbers, letters, signs), sounds, images encoded using the numbers 0 and 1.
Computer memory - a set of devices for storing information.
In the process of developing computer technology, people voluntarily or involuntarily tried to design and create various technical information storage devices in the image and likeness of their own memory. To better understand the purpose and capabilities of various computer storage devices, we can draw an analogy with how information is stored in a person's memory.
Can a person store all the information about the world around him in his memory and does he need it? Why, for example, remember the names of all the towns and villages in your area, when, if necessary, you can use a map of the area and find everything that interests you? There is no need to remember the prices of train tickets in different directions, as there are information services for this. And how many all kinds of mathematical tables exist, where the values of some complex functions are calculated! In search of an answer, you can always refer to the appropriate directory.
The information that a person constantly stores in his internal memory is characterized by a much smaller volume compared to the information concentrated in books, films, video cassettes, disks and other material media. We can say that the material media used to store information constitute the external memory of a person. In order to use the information stored in this external memory, a person must spend much more time than if it were stored in his own memory. This disadvantage is compensated by the fact that external memory allows you to save information for an arbitrarily long time and many people can use it.
There is another way of storing information by a person. A baby that has just been born already carries external features and, in part, a character inherited from its parents. This is the so-called genetic memory. A newborn can do a lot: breathes, sleeps, eats... A connoisseur of biology will remember unconditioned reflexes. This kind of internal human memory can be called constant, unchanging.
A similar principle of memory sharing is used in the computer. All computer memory is divided into internal and external. Similar to human memory, the internal memory of a computer is fast, but has a limited capacity. Working with external memory requires much more time, but it allows you to store an almost unlimited amount of information.
Inner memory consists of several parts: operational, permanent and cache memory. This is due to the fact that the programs used by the processor can be conditionally divided into two groups: temporary (current) and permanent use. Programs and temporary data are stored in RAM and cache only as long as the computer is powered on. After turning it off, the part of the internal memory allocated for them is completely cleared. Another part of the internal memory, called permanent, is non-volatile, that is, the programs and data recorded in it are always stored, regardless of whether the computer is turned on or off.
External memory computer, by analogy with how a person usually stores information in books, newspapers, magazines, on magnetic tapes, etc., can also be organized on various material media: floppy disks, hard drives, magnetic tapes, laser disks (compact -disks).
The classification of types of computer memory by purpose is shown in Figure 18.1.
Consider the characteristics and concepts common to all types of memory.
There are two common memory operations - reading (reading) information from memory and writing it to memory for storage. Addresses are used to access areas of memory.
When reading a portion of information from memory, a copy of it is transferred to another device, where certain actions are performed with it: numbers are involved in calculations, words are used to create text, a melody is created from sounds, etc. After reading, information does not disappear and is stored in that same area of memory until other information is written in its place.
Rice. 18.1. Types of computer memory
When recording (saving) pieces of information, the previous data stored at that location is erased. Newly recorded information is stored until another one is written in its place.
Read and write operations can be compared to the playback and recording procedures you know in everyday life performed with a conventional cassette recorder. When you listen to music, you read the information stored on the tape. In this case, the information on the tape does not disappear. But after recording a new album of your favorite rock band, the information previously stored on the tape will be erased and lost forever.
Reading (reading) information from memory is the process of obtaining information from a memory area at a given address.
Recording (saving) information in memory is the process of placing information in memory at a given address for storage.
The method of accessing a memory device for reading or writing information is called access. This concept is associated with such a memory parameter as access time, or memory speed - the time required to read from memory or write a minimum portion of information to it. Obviously, for the numerical expression of this parameter, time units are used: millisecond, microsecond, nanosecond.
Access time, or performance, memory - the time required to read from memory or write to it the minimum portion of information.
An important characteristic of memory of any kind is its size, also called capacity. This parameter indicates the maximum amount of information that can be stored in memory. The following units are used to measure the amount of memory: bytes, kilobytes (KB), megabytes (MB), gigabytes (GB).
The amount (capacity) of memory is the maximum amount of information stored in it.
Inner memory
The characteristic features of internal memory compared to external memory are high speed and limited volume. Physically, the internal memory of a computer is integrated circuits (chips) that are placed in special stands (sockets) on the board. The larger the internal memory, the more complex the task and the faster the computer can solve.
Non-volatile memory stores information that is very important for the normal operation of the computer. In particular, it contains the programs necessary to check the main devices of the computer, as well as to load the operating system. Obviously, these programs cannot be changed, since any intervention will immediately make it impossible to use the computer later. Therefore, only reading the information stored there permanently is allowed. This property of permanent memory explains its often used English name Read Only Memory (ROM) - read-only memory.
All information recorded in permanent memory is retained even after the computer is turned off, since the microcircuits are non-volatile. Writing information to permanent memory usually occurs only once - during the production of the corresponding chips by the manufacturer.
Read-only memory is a device for long-term storage of programs and data.
There are two main types of permanent memory chips: once-programmable (after writing, the contents of the memory cannot be changed) and repeatedly programmable. The content of the repeatedly programmable memory is changed by means of electronic influence.
RAM stores information necessary to execute programs in the current session: initial data, commands, intermediate and final results. This memory only works when the computer is powered on. After turning it off, the contents of the RAM are erased, since microcircuits are volatile devices.
RAM is a device for storing programs and data that are processed by the processor in the current session.
The RAM device provides modes of recording, reading and storing information, and at any time access to any memory cell is possible. Random access memory is often referred to as RAM (Random Access Memory).
If you need to store the results of processing for a long time, then you should use some kind of external storage device.
NOTE!
When you turn off the computer, all information in RAM is erased.
RAM is characterized by high speed and relatively small capacity.
RAM chips are mounted on a printed circuit board. Each such board is equipped with contacts located along the bottom edge, the number of which can be 30, 72 or 168 (Figure 18.2). To connect to other computer devices, such a board is inserted with its contacts into a special connector (slot) on the system board located inside the system unit. The motherboard has several slots for memory modules, the total amount of which can take on a number of fixed values, for example, 64, 128, 256 MB and more.
Rice. 18.2. Microcircuits (chips) of RAM
Cache (English cache - cache, warehouse) is used to increase computer performance.
Cache memory is used in the exchange of data between the microprocessor and RAM. The algorithm of its operation allows to reduce the frequency of microprocessor accesses to RAM and, consequently, to increase computer performance.
There are two types of cache memory: internal (8-512 KB), which is located in the processor, and external (256 KB to 1 MB), installed on the motherboard.
External memory
The purpose of the external memory of a computer is to store information of any kind for a long time. Turning off the computer's power does not clear the external memory. This memory is thousands of times larger than the internal memory. In addition, if necessary, it can be "built up" in the same way as you can buy an additional bookshelf to store new books. But accessing external memory takes much more time. Just as a person spends much more time searching for information in reference literature than searching for it in his own memory, so the speed of accessing (accessing) external memory is much greater than that of operational memory.
It is necessary to distinguish between the concepts of a storage medium and an external memory device.
A carrier is a material object capable of storing information.
An external memory device (drive) is a physical device that allows reading and writing information to the appropriate media.
Information carriers in the external memory of modern computers are magnetic or optical disks, magnetic tapes and some others.
According to the type of access to information, external memory devices are divided into two classes: direct (random) access devices and sequential access devices.
In devices of direct (random) access, the time of accessing information does not depend on its location on the media. In serial access devices, such a dependency exists.
Let's look at familiar examples. The access time for a song on an audio cassette depends on the location of the recording. To listen to it, you must first rewind the cassette to the point where the song was recorded. This is an example of sequential access to information. The time of access to a song on a phonograph record does not depend on whether this song is the first or the last one on the disc. To listen to your favorite work, it is enough to place the player's pickup in a certain place on the disk where the song is recorded, or indicate its number on the music center. This is an example of direct access to information.
In addition to the previously introduced general memory characteristics for external memory, the concepts of recording density and information exchange rate are used.
Recording Density determined by the amount of information recorded per unit track length. Recording density is measured in bits per millimeter (bits/mm). The recording density depends on the density of the tracks on the surface, that is, the number of tracks on the surface of the disc.
Recording DENSITY - the amount of information recorded per unit track length.
Information exchange rate
depends on the speed of its reading or writing to the media, which, in turn, is determined by the speed of rotation or movement of this media in the device. According to the method of writing and reading, external memory devices (drives) are divided depending on the type of media into magnetic, optical and electronic (flash memory). Consider the main types of external storage media.
Flexible magnetic disks
One of the most common storage media are floppy disks (floppy disks) or floppy disks (from the English floppy disk). Floppy disks with an outer diameter of 3.5" (in.), or 89 mm, commonly referred to as 3" are now widely used. Disks are called flexible because their working surface is made of elastic material and placed in a hard protective envelope. For access to The magnetic surface of the disc in the protective envelope has a window closed by a shutter.
The surface of the disk is covered with a special magnetic layer. It is this layer that provides storage of data represented by a binary code. The presence of a magnetized surface area is coded as 1, the absence is coded as 0. Information is recorded from both sides of the disk on tracks that are concentric circles (Figure 18.3). Each track is divided into sectors. Tracks and sectors are magnetized areas of the disc surface.
Working with a floppy disk (writing and reading) is possible only if it has magnetic markings for tracks and sectors. The procedure for preliminary preparation (marking) of a magnetic disk is called formatting. To do this, a special program is included in the system software, with the help of which the disk is formatted.
Rice. 18.3. Surface marking of a floppy disk
Formatting a disk is the process of magnetically marking a disk into tracks and sectors.
To work with floppy disks, a device called a floppy disk drive, or a floppy disk drive (FDD) is designed. The floppy drive belongs to the group of direct access drives and is installed inside the system unit.
A floppy disk is inserted into the drive slot, after which the shutter automatically opens and the disk rotates around its axis. When an appropriate program accesses it, a magnetic write / read head is installed over the sector of the disk where information needs to be written or from where it is required to read information. To do this, the drive is equipped with two stepper motors. One motor rotates the disk inside the protective envelope. The higher the rotation speed, the faster the information is read, which means that the speed of information exchange increases. The second engine moves the write/read head along the radius of the disk surface, which determines another characteristic of external memory - the information access time.
The protective envelope has a special write protection window. This window can be opened or closed using the slider. To protect information on the disk from being changed or deleted, this window is opened. In this case, writing to the floppy disk becomes impossible and only reading from the disk remains available.
To refer to a disk installed in the drive, special names are used in the form of a Latin letter with a colon. The presence of a colon after the letter allows the computer to distinguish the drive name from the letter, as this is a general rule. The drive for reading information from a 3-inch disk is given the name A: or sometimes B:.
Remember the rules for working with floppy disks.
1. Do not touch the working surface of the disc with your hands.
2. Keep discs away from a strong magnetic field such as a magnet.
3. Do not expose discs to heat.
4. It is recommended to make copies of the contents of floppy disks in case of damage and failure.
The volume stored on a magnetic disk can be significantly increased by technologies that additionally use information compression (ZIP disk) when recording.
Hard magnetic disks
One of the essential components of a personal computer are hard drives. They are a set of metal or ceramic discs (package of discs) coated with a magnetic layer. Disks, together with a block of magnetic heads, are installed inside a sealed drive housing, usually called a hard drive. A hard disk drive (hard drive) refers to drives with direct access.
The term "winchester" originated from the slang name for the first 16 kb hard drive (IBM, 1973), which had 30 tracks of 30 sectors, which coincidentally coincided with the 30"/30" caliber of the famous Winchester hunting rifle.
Main features of hard drives:
♦ hard disk belongs to the class of media with random access to information;
♦ to store information, the hard disk is marked into tracks and sectors;
♦ to access information, one disk drive motor rotates a pack of disks, the other sets the heads to the place where information is read/written;
♦ The most common hard drive sizes are 5.25 and 3.5 inches in outer diameter.
A hard disk is a very complex device with high-precision read/write mechanics and an electronic board that controls the operation of the disk. To preserve the information and performance of hard drives, it is necessary to protect them from shocks and sudden shocks.
Hard drive manufacturers have focused their efforts on creating hard drives with greater capacity, reliability, data transfer speed and less noise. The following main trends in the development of hard magnetic disks can be distinguished:
♦ development of hard drives for mobile applications (for example, one-inch, two-inch hard drives for laptops);
♦ development of non-PC applications (TVs, VCRs, cars).
To access the hard disk, use the name specified by any Latin letter, starting with C:. If a second hard disk is installed, it is assigned the following letter of the Latin alphabet D:, etc. For convenience, the operating system provides the ability to conditionally split one physical disk into several independent parts, called logical disks, using a special system program. In this case, each part of one physical disk is assigned its own logical name, which allows you to independently access them: C:, D:, etc.
Optical discs
Optical or laser media These are disks on the surface of which information is recorded using a laser beam. These discs are made of organic materials with a thin layer of aluminum sprayed on the surface. Such discs are often called CDs or CDs (English Compact Disk - CD). Laser discs are currently the most popular storage media. With dimensions (diameter - 120 mm) comparable to floppy disks (diameter - 89 mm), the capacity of a modern CD is about 500 times greater than that of a floppy disk. The capacity of a laser disc is approximately 650 MB, which is equivalent to storing text information of approximately 450 books or a sound file of 74 minutes.
Unlike magnetic discs, a laser disc has one track in the form of a spiral. Information on a track-spiral is recorded by a powerful laser beam, which burns depressions on the surface of the disk, and is an alternation of depressions and bulges. When reading information, the protrusions reflect the light of a weak laser beam and are perceived as a unit (1), the cavities absorb the beam and, accordingly, are perceived as zero (0).
The non-contact method of reading information using a laser beam determines the durability and reliability of CDs. Like magnetic, optical disks are devices with random access to information. The optical disk is assigned a name - the first free letter of the Latin alphabet, not used for hard disk names.
There are two types of drives (optical drives) for working with laser discs:
♦ a CD-ROM reader that only reads information previously written to the disc. This is the reason for the name of the optical drive CD-ROM (from the English. Compact Disk Read Only Memory - a read-only CD). The impossibility of recording information in this device is explained by the fact that it has a source of weak laser radiation, the power of which is only enough to read information;
♦ an optical drive that allows not only reading but also writing information to a CD. It's called CD-RW (Rewritable). CD-RW devices have a sufficiently powerful laser that allows you to change the reflectivity of surface areas during the recording process and burn microscopic depressions on the surface of the disc under the protective layer, thereby recording directly in the computer's drive.
DVDs, like CDs, store data by arranged bulges (notches) along spiral tracks on a reflective, plastic-coated metal surface. The laser used in DVD recorders/readers creates smaller notches, which allows increasing the data recording density.
The incorporation of a translucent layer that is transparent to light of one wavelength and reflects light of another wavelength makes it possible to create two-layer and two-sided discs and therefore increase the capacity of the disc at the same size. At the same time, the geometric dimensions of DVD and CD are the same, which made it possible to create devices capable of reproducing and recording data both on CD and DVD. But it turned out that this is not the limit. DVD video and audio uses sophisticated data compression technology to fit even more information into a smaller space.
Magnetic tapes
Magnetic tapes are media similar to those used in home audio cassette recorders. A device that provides recording and reading information from magnetic tapes is called a streamer (from the English stream - flow, flow; flow). The streamer refers to devices with sequential access to information and is characterized by a much lower speed of writing and reading information compared to disk drives.
The main purpose of streamers is the creation of data archives, backup, and reliable storage of information. Many large banks, commercial firms, commercial enterprises transfer important information to magnetic tapes at the end of planning periods and put the cassettes in archives. In addition, information from the hard drive is periodically written to the streamer cassettes in order to use it in the event of an unforeseen failure of the hard drive, when it is necessary to urgently restore the information stored on it.
Flash memory
Flash memory refers to an electronic non-volatile type of memory. The principle of operation of flash memory is similar to the principle of operation of computer RAM modules.
The main difference is that it is non-volatile, that is, it stores data until you delete it yourself. When working with flash memory, the same operations are used as with other media: writing, reading, erasing (deleting).
Flash memory has a limited lifespan, which depends on the amount of information being overwritten and how often it is updated.
Comparative characteristics
Modern computers, as a rule, have external memory consisting of: a hard drive, a drive for 3.5-inch floppy disks, CD-ROM, flash memory. It should be remembered that magnetic disks and tapes are sensitive to magnetic fields. In particular, placing a strong magnet near them can destroy the information stored on these media. Therefore, when using magnetic media, it is necessary to ensure their remoteness from sources of magnetic fields.
Table 18.1 compares the memory sizes of the most common modern memory devices and storage media discussed earlier.
Table 18.1. Comparative characteristics of memory devices
personal computer, August 2006
Control questions and tasks
1. The capacity of a 3.5" floppy disk is 1.44 MB. A laser disc can contain 650 MB of information. Determine how many floppy disks will be needed to accommodate the information from one laser disk.
2. The diameter of floppy disks is specified in inches. Calculate the floppy disk dimensions in centimeters (1 inch = 2.54 cm).
3. It has been established that 1 byte of memory is required to write one character. In a notebook in a cell, consisting of 18 sheets, we write one character in each cell. How many notebooks can be written on one floppy disk with a memory capacity of 1.44 MB?
4. Determine the amount of memory required to store 2 million characters. How many 1.44 MB disks will be needed to record this information?
5. Your hard drive has a capacity of 2.1 GB. The speech recognition device perceives information at a maximum rate of 200 letters per minute. How long does it take to fill up 90% of the hard disk space?
6. What is the purpose of information storage devices in a computer?
7. What types of memory do you know and what is their main difference?
8. What is external memory used for when working on a personal computer?
9. What is the essence of reading and writing information into memory?
10. What characteristics do you know that are common to all types of memory?
11. What characterizes the internal memory of a computer?
12. What are the features of permanent memory?
13. What are the features of RAM?
14. What are the features of cache memory?
15. Specify the distinguishing features of the internal and external memory of the computer.
16. What specific characteristics of external memory do you know?
17. List the carriers of information known to you from ancient times to the present day. Arrange them in chronological order.
18. Give a brief description of the most common storage media used in a computer.
19. What is the difference between direct and sequential access to information on media?
20. Specify the general properties and distinctive features of floppy and hard drives.
21. What is CD, CD-ROM, CD-R?
22. When is it appropriate to use a streamer?
23. Complete Table 18.1 with the data for your specific computer model.
Any electronic computers include memory drives. Without them, the operator would not be able to save the result of his work or copy it to another medium.
Punch cards
At the dawn of its appearance, punched cards were used - ordinary cardboard cards with printed digital markings.
One punched card contained 80 columns, each column could store 1 bit of information. The holes in these columns corresponded to the unit. The data was read sequentially. It was impossible to re-record anything on a punch card, so a huge number of them were required. It would take 22 tons of paper to store a 1 GB data array.
A similar principle was used in perforated tapes. They wound on a reel, took up less space, but often torn and did not allow you to add and edit data.
floppy disks
The advent of floppy disks was a real breakthrough in information technology. Compact, capacious, they allowed to store from 300 KB on the earliest samples to 1.44 MB on the latest versions. Reading and writing were carried out on a magnetic disk enclosed in a plastic case.
The main disadvantage of diskettes was the fragility of the information stored on them. They were vulnerable to action and could be demagnetized even in public transport - a trolleybus or tram, so they tried not to use them for long-term data storage. Floppy disks were read in disk drives. At first there were 5-inch floppy disks, then they were replaced by more convenient 3-inch ones.
Flash drives have become the main competitor of floppy disks. Their only drawback was the price, but as microelectronics developed, the cost of flash drives dropped dramatically and floppy disks became history. Their production was finally discontinued in 2011.
streamers
Streamers were previously used to store archived data. They were similar to video cassettes in appearance and in principle. A magnetic tape and two reels made it possible to sequentially read and write information. The capacity of these devices was up to 100 MB. Such drives have not received mass distribution. Ordinary users preferred to store their data on hard drives, and it was more convenient to keep music, movies, programs on CDs and later DVDs.
CD and DVD
These storage media are still in use today. An active, reflective and protective layer is applied to the plastic substrate. Information from the disc is read by a laser beam. A standard disk has a capacity of 700 MB. This is enough for example to record a 2-hour movie in average quality. There are also double-sided discs where the active layer is deposited on both sides of the disc. Mini-CDs are used to save a small amount of information. Drivers, instructions for computer products are now written on them.
DVDs replaced CDs in 1996. They allowed to store information already in the amount of 4.7 GB. Their advantage was also that the DVD drive could read both CDs and DVDs. At the moment it is the most massive memory storage device.
Flash drives
The CD and DVD drives discussed above have a number of advantages - cheapness, reliability, the ability to store large amounts of information, but they are designed for one-time recording. You cannot make changes, add or remove unnecessary things on a recorded disc. And here a fundamentally different drive comes to our aid - flash memory.
For some time he competed with floppy disks, but quickly won this race. The main limiting factor was the price, but now it has been reduced to an acceptable level. Modern computers are no longer equipped with disk drives, so the flash drive has become an indispensable companion for everyone dealing with computer technology. The maximum amount of information that can fit on a flash drive reaches 1 Tb.
Memory cards
Phones, cameras, e-books, photo frames and much more require memory drives to work. Due to their relatively large size, USB sticks are not suitable for this purpose. Memory cards are specially designed for such cases. In fact, this is the same flash drive, but adapted for small-sized products. Most of the time, the memory card is in an electronic device and is removed only to transfer the accumulated data to a permanent medium.
There are many standards for memory cards, the smallest of them are 14 by 12 mm. On modern computers, instead of a disk drive, a card reader is usually installed, which allows you to read most types of memory cards.
Hard drives (HDD)
Memory drives for a computer are inside it there are metal plates coated on both sides with a magnetic composition. The motor rotates them at a speed of 5400 for older models or 7200 rpm for modern devices. The magnetic head moves from the center of the disk to its edge and allows you to read and write information. The volume of the hard drive depends on the number of disks in it. Modern models allow you to store up to 8 Tb of information.
There are practically no shortcomings of this type of memory drives - they are very reliable and durable products. The cost of a unit of memory in hard drives is the cheapest among all types of drives.
Solid state drives (SSD)
No matter how good hard drives are, they have almost reached their ceiling. Their performance depends on the speed of disk rotation, and its further increase leads to physical deformation. Flash technology, which is used in the manufacture of solid-state memory drives, is devoid of these disadvantages. They do not contain moving parts, so they are not subject to physical wear and tear, are not afraid of shock and do not make noise.
But there are still serious shortcomings. First of all - the price. The cost of a solid state drive is 5 times higher than a hard drive of the same size. Another significant drawback is a short service life. Solid state drives are usually chosen for installing the operating system, and a hard drive is used for data storage. The cost of solid-state drives is steadily declining, and there is progress in increasing their resource. In the near future, they should replace traditional hard drives, just as flash drives replaced floppy disks in their time.
External drives
Internal storage and internal memory are good for everyone, but often you need to transfer information from one computer to another. Back in 1995, the USB interface was developed, which allows you to connect a wide variety of devices to a PC, and memory drives are no exception. Initially, these were flash drives, later DVD players with a USB connector appeared, and finally HDD and SSD drives.
The attractiveness of the USB interface is in its simplicity - just plug in a USB flash drive or other storage device and you can work, no driver installation or other additional steps are required. The development of the interface and the appearance of USB 2.0 first, and then USB 3.0, dramatically increased the speed of data exchange over this channel. The performance now differs little from the internal one, and their size cannot but rejoice. An external memory drive fits easily in the palm of your hand, while it allows you to store hundreds of gigabytes of information.
Information carriers (flexible and hard disks, CD-ROM disks).
The main purpose of the external memory of a computer is the long-term storage of a large number of different files (programs, data, etc.). The device that provides writing / reading information is called a drive, and information is stored on media. The most common types of drives are:
Floppy disk drives (3.5" floppy disks (capacity 1.44 MB);
Hard disk drives (HDD) with information capacity up to 200 GB;
CD-ROM drives for CD-ROMs with a capacity of 700-800 MB.
For the user, some technical and economic indicators are essential: information capacity, information exchange rate, reliability of its storage, and, finally, the cost of the drive and media to it
The recording, storage and reading of information is based on two physical principles, magnetic and optical. The floppy disk drive and hard disk drive use the magnetic principle. With the magnetic method, information is recorded on a magnetic medium (a disk coated with a ferromagnetic varnish) using magnetic heads.
The storage media is disk-shaped and placed in a plastic case (3.5"). In the center of the disk there is a hole (or gripping device) to ensure that the disk rotates in the drive, which is performed at a constant angular speed of 300 rpm.
The protective envelope (body) has an elongated hole through which information is written / read. On 3.5" floppy disks, write protection is provided by a safety latch in the lower left corner of the plastic case.
The disk must be formatted, i.e. the physical and logical structure of the disk must be created. During the formatting process, concentric tracks are formed on the disk, which are divided into sectors; for this, the drive head places track and sector marks in certain places on the disk.
Hard magnetic disks consist of several disks placed on the same axis and rotating at a high angular velocity (several thousand revolutions per minute), enclosed in a metal case. The large information capacity of hard disks is achieved by increasing the number of tracks on each disk to several thousand, and the number of sectors per track to several tens.
CD-ROM drives use the optical principle of reading information. Information on a CD-ROM is recorded on a single spiral track (like on a gramophone record) containing alternating sections with different reflectivity. The laser beam falls on the surface of a rotating CD-ROM disk, the intensity of the reflected beam corresponds to the values 0 or 1. With the help of a photoconverter, they are converted into a sequence of electrical impulses,
The speed of reading information in a CD-ROM drive depends on the speed of rotation of the disk.
CD-ROMs are produced either by stamping (white discs) or recorded (yellow discs) on special devices called CD-recorder.
External memory
External memory- this is memory implemented in the form of external (relative to the motherboard) storage devices (VZU) with different principles of information storage.VZU are intended for long-term storage of information of any kind and are characterized by a large amount of memory and low speed compared to RAM.
External memory of a computer is usually understood as a device for reading / writing information - drives, and devices where information is directly stored - carriers information.
As a rule, each storage medium has its own drive. And such a device as a hard drive, combines both the media and the drive.
Information carriers in the external memory of modern computers are magnetic and optical disks, magnetic tapes and some others.
The main types of external (long-term) memory devices by recording method are:
In personal computers, external memory devices include:
- Floppy disk drives designed to read/write information on floppy disks (floppy disks);
- Hard disk drives, or hard drives;
- disk drives for working with laser (optical) disks;
- streamers designed to read / write information to magnetic tapes;
- Magneto-optical drives for working with magneto-optical disks;
- Non-volatile memory devices (flash memory).
According to the type of access to information, external memory devices are divided into two classes:
- Devices direct (random) access.
In devices of direct (random) access, the time of accessing information does not depend on its location on the media. For example, to listen to a song recorded on a phonograph record, it is enough to place the turntable's pickup in the place on the record where the song is recorded.- Devices sequential access.
In serial access devices, such a dependency exists. For example, the access time to a song on an audio cassette depends on the location of the recording. To listen to it, you must first rewind the cassette to the point where the song was recorded.
The capacity of external memory is hundreds and thousands of times greater than the capacity of RAM or generally unlimited when it comes to drives with removable media.
- Capacity (volume)- the maximum amount of information (amount of data) that can be written to the media.
- Performance is determined by the time of access to the necessary information, the time of its reading / writing and the data transfer rate.
But accessing external memory requires much more time, since the speed of external memory is significantly lower than that of RAM.
