During an epoch of origin of the mass market of the house multimedia systems, the fallen last quarter of the twentieth century, practically all arrangements were analogue. The information was written to rather big holders. In development they were replaced by compact variants of carriers
In the market of the videosystems which have banked audio and video, the greatest distribution have received the holders of format VHS used in stationary arrangements. They provide the permission to 250 strings of the map.
Tape width — 0,5 inches (12,65 mm). Writing is made by means of two video heads allocated on the opposite ends of the roll under a corner of 180 degrees. The given format provides various write modes of playback: SP, LP, EP. They are characterised by different speeds of writing-playback. For standard PAL speeds 23,39mm/c (standard, SP) and 11,695 mm/with (long-playing, longplay — LP), for standard NTSC — 11,12 mm/c (EP) are provided .
Development of the given standard of a steel of holder Super VHS (S-VHS). They have provided more excellence of the map which have reached of 400 strings. However in the domestic market they all the same have not received high distribution.
It is necessary to mark, that holders VHS became the popular carrier not only for video, but also for an audioinformation high-fidelity recording. It is provided with some types of videounits. By the way, in the late eighties – the beginning of the ninetieth the given holders were successfully applied to storage of the computer information.
On the basis of the analogue formats providing usage of rather big holders, the compact variant has been specially developed. It has received name C-VHS and began to be applied to appropriate analogue videocameras.
As alternative, SONY corporation has developed format Video-8. Actually this format is in many respects repetition of format VHS. Distinctive feature is the width of a film which has made 8 mm that has allowed to reduce the videocassette size. As to quality of the video map it is necessary to mark, for Video-8 it corresponded VHS. Small dimensions of the holder have allowed to release a series of the compact videocameras which have received name Handycam. A little bit later format Hi-8 has been released. The tape width was the same, as for Video-8. This format had much in common with S-VHS.
From analogue to the digital
Analogue formats remained mass long time. However they possess a number of serious lacks:
· poor quality of writing,
· quality lowering at overwriting,
· step-by-step lowering of quality at multiple playback,
· the limited period of storage of a substance,
· the big holder and the heavy arrangement.
To be saved of the specified problems it was possible only transition to the digital ways of writing meaning usage of appropriate arrangements and carriers. The main advantages are:
· durability of saving of the information, limited only periods of "life" of the carrier,
· absence of loss of quality at multiple overwriting (the tenth copy which becomes with the ninth which …, completely coincides with the original).
Format Digital-8 providing constructive compatibility with analogue holders of formats Video-8 and Hi-8 became a major landmark in formation of the market of compact digital videocameras.
However thanks to new processing techniques high-quality miniature components have been created. Added with appropriate carriers, they have allowed to reduce dimensions of videounits. First of all it concerns videocameras.
The considerable role in formation of the market of the arrangements providing writing of a video information, was provided with development of standard DV, holders MiniDV became a home which variant of implementation.
From technical characteristics it is necessary to mark a high-resolution in a frame — 720х576 pikselov. This standard is more qualitative not only analogue VHS, but even Super VHS. Holders MiniDV became the standard in the world of videocameras. Their size making 66х48х12 mm (more match the box) allows to provide with the little small dimensions of cameras. As to the sizes of holders the visualisation gives the Photo 1.
Photo 1. Videocassettes VHS and MiniDV
Replaceable carriers of a video information
Photo 2. Replaceable media: holder MiniDV, disk DVD, card SD
On the Photo 2 examples of the widespread, popular replaceable media are presented. These carriers widely use in advanced models of videocameras.
The greatest distribution was received by magnetic tapes MiniDV calculated for support of the digital format with the same name, representing home version DV.
Compression of the written information before writing on a magnetic film is carried out five times. As a result on standard holder MiniDV in mode SP (Standard Play - usual playing) is located 60 minutes of writing, and in mode LP (Long Play - long playing) — till 90 minutes of writing.
The sound digital recording can be made according to one of three modes:
· one stereochannel (i.e. Two audiotracks) 16-bit, 44,1 kgts (corresponds to CD-quality);
· one stereochannel 16-bit, 48 kgts (DAT-quality);
· two stereochannels (four tracks) 12-bit, 32 kgts.
Thus the sound is not compressed.
From the main advantages of the videocameras oriented to usage MiniDV of holders, it is necessary to select small dimensions, an accurate freeze frame, marking and marking of the finished shooting plots directly on a videocamera, support of time codes.
Holders MiniDV with a thin, narrow tape possess small dimensions and weight. The Tape recording is carried out by series of oblique labels by means of the miniature magnetic heads fixed on the spun roll. Such roll is resulted at centre of the Photo 3 on which the fragment of the tape drive of videocamera MiniDV is presented.
Photo 3. A fragment of the tape drive of videocamera MiniDV
Speed of rotation of the roll of 9000 turns. The size of a label written to a tape makes 10 microns in mode SP and 6.7 microns in mode LP a mode. The tape moves with a speed of 18.8 mm/sek in mode SP and 12.5 mm/sek in mode LP.
Standard parametres of a tape cartridge are presented in the table.
Standard parametres of magnetic tapes MiniDV 60
Write time in mode SP, mines
Write time in mode LP, mines
The information content, written to holder MiniDV for 60 minutes (mode SP), makes about 14 Gbytes. In mode LP the information capacity increases in one and a half time and reaches about 20 Gbytes. By the way, among replaceable carriers the given holders provide very low cost of an information storage. Really, the price 60 minute (SP) the firm holders, depending on the corporation-manufacturer, suppliers and sellers, averages now $5. However on the Internet meet the price and less than $3.
It is necessary to mark, that there are even more capacious holders, the truth, and essentially more expensive. They provide time of writing/playback with duration 80 and even 120 minutes in mode SP. It is obvious, that their application in mode LP increases writing/playback time in one and a half time, that is it will make accordingly 120 and 180 minutes. However before usage of these holders it is necessary to estimate not only advantages, but also their lacks. Perhaps main disadvantage consists in essential higher price, which several times above the price of the standard holder calculated for 60 minutes in mode SP. Besides, increased time of writing/playback is reached at the expense of usage of more thin tapes. Their maintenance demands high-quality, faultlessly working tape drives, that not always takes place, especially in inexpensive videocameras. But also in expensive models it is not easy to provide, as even small foreign matter of magnetic heads, the roll and other units of the tape drive, quite admissible in case of the standard holder, can lead zamjatiju a thin tape and to information corrupting on this site.
For reaching of maximum time of the service of the magnetic tape and support of long time of an information storage it is necessary to store holders correctly.
The temperature indoors should be supported at level of 18-25 degrees of Celsius, humidity — at level of 50-80 %. Sharp temperature drops and humidity are inadmissible in order to avoid condensation of water steams on a tape, tank and sliding parts of the mechanism of the holder.
Holders should be held without fail in the standard plastic boxes protecting from mechanical damages, dust penetrations etc.
To store holders it is necessary in vertical position that reduces probability of deformation of a tape and the subsequent damage of the mechanism of a videocamera.
Not to admit effect of the strong electromagnetic fields, capable to degauss a tape.
Not used holders it is recommended periodically (time in half a year) to rewind for removal of mechanical powers and static charges.
The holder brought in a premise from a frost, it is expedient to soak, not opening a plastic box, at normal temperature of 3-5 hours and only then to insert into a videocamera. In no event it is impossible to touch a tape fingers, fatty prints carry on to its damage.
It is not recommended to gain the holder of an unknown origin.
Before usage of their new tapes it is expedient to complete wind that reduces probability of "fallout" of the information at writing to subject.
Analogue video tapes soak some tens overwritings, digital — to hundred and more. Under the informal information of manufacturers of modern magnetic media and experience of archive storage of older, writings on not worn out holders are saved without considerable deterioration till 50 years.
Despite advantages of magnetic tapes, as replaceable carriers the last years the wide circulation was received by optical disks.
At the initial stage it were CD. However in further they were rather fast replaced DVD which differ from usual CD-ROMs, by CD-R, CD-RW bolshej information capacity. Here it is necessary to remind, that DVD (Digital Versatile Disk, a digital general-purpose disk) supports the modern standard of an information storage on optical disks, data record on which is carried out by means of a laser beam.
There are different variants of disks DVD. However in videocameras have found a wide circulation disks of diameter of standards DVD-R of 8 sm (unitary writing) and DVD-RW (multiple writing). The given disks can both one-sided, and double-side. In the latter case the information capacity doubles, as there is a possibility to write the information on both sides.
Single-sided disks DVD-R/-RW of diameter of 8 sm possess size of 1,4 Gbytes, and double-side — 2,8 Gbytes. Concrete numerical estimations of time of writing/playback depend on the write modes which basic performance are a transfer rate — bitrejt (bitrate). The Same parametre depends on used algorithms of compression of the written information. Thus the above the aspect ratio, the is more time of writing/playback for one disk. However it is necessary to consider, that strong compression of the information is accompanied by appropriate deterioration. Usually the write mode choice, and, therefore, and writing/playback time is given to the user. As an example it is possible to result videocamera Canon DC20 having three modes — three speeds, providing time of writing/playback for double-side disks DVD-R/-RW within 40, 60, 120 minutes, at bitrejtah 9, 6, 3 Mbit/with.
The price of disks DVD-R/-RW depends on the corporation-manufacturer, suppliers and sellers. In the present the price of 1,4 Gbytes of 8 sm DVD-R averages $3, but the Internet meet the price and less than $1, disks DVD-R of 2,8 Gbytes are more expensive approximately in 3 times. Even more expensively disks DVD-RW.
That after the writing termination the given carrier can be installed at once in the optical drive of the desktop computer or a notebook concerns indisputable advantages of optical disks.
At all advantages enumerated above carriers operation with them demands mechanisms in which construction moving units use.
Specificity of the given mechanisms demands precision fulfilment and quite often labour-consuming customisation of their components. It affects the price of the finite products which resource of operation is limited to a considerable quantity of continuously moving units. And in addition to this list of lacks it is necessary to mark, that operation of such mechanisms is accompanied by rather high power consumption.
Break is possible only changeover of informational carriers by such types which in the operation do not demand moving parts. As such carriers memory cells can appear.
Unfortunately, the traditional semiconducting memory used in computers, for this role is not necessary in sort of a high relation of the price and size. In addition it does not have not enough compactness. And such memory is volatile. It means, that the information fails at power supplies turn off. The given circumstance does practically impossible the replaceable carriers created on the basis of traditional units.
From the marked lacks flash-memory cards are free. They are non-volatile, compact and unlike holders with the magnetic tape and optical disks do not demand for the functioning of mechanisms with moving units. In addition to it the size of serial cards of the flash-memory reaches now already 4 Gbytes, that while 14 Gbytes of holders MiniDV 60 there are less , but exceeds 2,8 Gbytes of double-side 8 sm of optical disks DVD-R/-RW.
Now there are some types of cards of the flash-memory differing as konstruktivom, and standards hooking up (interfaces). However the most widespread and popular are cards SD (Secure Digital) and their more compact modifications miniSD.
It is necessary to mark, that cards SD and МiniSD are released by different manufacturers, have different size and a different transfer rate.
Mesh sizes of cards SD do by their perspective carriers of video and the audioinformation.
Unfortunately, their price if it to compare to cost of alternative carriers while it is high enough. Therefore while this type of the replaceable carrier uses for a data recording a little. And in such videocameras while it is impossible to name quality of the map high as from economic reasons low values of permissions use. Besides, in such videocameras very high aspect ratioes are applied, that inevitably carries on to information loss.
However the price fast decreases (in 1,5-2 times a year). Now cost of 1 Gbytes of electronic stuffing SD is estimated approximately in $30-40. Definitive cost of cards SD depends as on size, and high-speed parametres. By the way, the integral characteristic of speed is resulted recently on card SD in the form of multiplicity coefficients, for example, 60х, 66х, 80х, 133х, 150х, etc. Optimal now it is possible to consider cards SD of 1 Gbytes 80х, but, of course, can use and others. For an exception of the errors linked to inconsistence with some models vysokoemkih (more than 1 Gbyte) high-speed (133х, 150х and above) cards SD, it is expedient to consult with experts.
The built in carriers
Except replaceable carriers, in the numerous products calculated for writing and playback of the multimedia information, hard disk drives (HDD) use also. Proceeding from tendency to minimisation of the sizes of audio and videounits, in their construction accessories of compact form factors are applied. Disk drives concern them with magnetic disks in diameter 1, 1,8, 2,5 inches. On the Photo 4 examples of models with disks of 1 and 2,5 inches made by company Seagate are resulted.
Photo 4. Models HDD with disks of 1 and 2,5 inches released by company Seagate
The size serial HDD with disks in diameter of 1 inch, released in million circulations, makes now 5 Gbytes. But the models which size reaches 10 Gbytes are declared .
The information capacity mass HDD with 2,5-inch disks has reached 160 Gbytes. However, disk drives of such size are released while only by company Seagate, but, considering power of the given manufacturer, it is possible to expect, that the next months their quantity will be already calculated by millions. But here HDD size of 100 Gbytes became already standard and are offered by all manufacturers.
As to disk drives with disks of 1,8 inches they occupy intermediate position, both on the sizes, and on size. But it does not prevent to occupy with it a considerable share of the market.
The specified disk drives use as the newest media providing both considerable size, and fast access to the information.
Estimating advantages of the given carriers, it is necessary to mark, that videos of the arrangement with such resources of storage of a multimedia content yet do not occupy a considerable share in total amount. However their share steadily raises, restricting sector of products with traditional holders MiniDV.
Article is published in log Magic of the PC.