Videoaccelerators

The image which we see on the screen of the monitor, represents deduced(removed) by special digit-analog converter RAMDAC (Random Access Memory Digital to Analog Converter) and the device of development(display) contents of videomemory. These contents can change both the central processor, and the graphic processor of a videomap — the accelerator two-dimensional schedules (synonyms: the 2D-accelerator, a 2D-accelerator, a Windows-accelerator or a GDI-accelerator). Modern window interfaces demand fast (for the tenth shares of second) copying of contents of the screen at opening / closing of windows, their moving, etc., differently the user will feel insufficiently fast reaction of system to his(its) actions. For this purpose the processor should process the data and pass them on the Bus with a speed, all in 2-3 times smaller, than speed of job RAMDAC, and is tens and even hundreds megabytes a second that is practically unreal even to modern measures. In due time for increase of speed of system local Buss, and later — 2D-accelerators which represent the specialized graphic processors capable independently to draw on the screen the cursor of the mouse, elements of windows and the standard geometrical figures stipulated GDI — have been developed by graphic library Windows. 2D-accelerators exchange the data with videomemory on the own Bus, not loading the system Bus of the processor. On the system Bus the 2D-accelerator receives only GDI-instructions from the central processor, thus the volume of the transmitted data and loading of the processor in hundreds times is less.

Modern 2D-accelerators have 64-or the 128-digit Bus of the data, and for an effective utilization of opportunities of this Bus on a videomap 2 or 4 Mb of videomemory accordingly should be established, differently the data will be passed on twice narrower Bus with corresponding loss in speed.

It is possible to say, that by the present(true) moment 2D-accelerators have reached(achieved) perfection. All of them work so quickly, that in spite of the fact that their productivity on special tests can differ from model to model on 10-15 %, the user, most likely, will not notice this distinction. Therefore at a choice of the 2D-accelerator it is necessary to pay attention to other factors: quality of the image, presence of additional functions, quality and functionality of the drivers, supported frequencies of a vertical sweep, compatibility with VESA (for fans(amateurs) of DOS-games), etc. Microcircuits of 2D-accelerators now make ATI, Cirrus Logic, Chips*Technologies, Matrox, Number Nine, S3, Trident, Tseng Labs and other companies.

As a multimedia - accelerators usually understand devices which besides acceleration of usual graphic operations can carry out also a number(line) of operations on processing the videodata from different sources.

First of all, it is functions on acceleration of a conclusion of video in formats AVI, Indeo, MPEG-1 and others. A problem that videofilm in format NTSC goes with speed of 30 staff in a second, PAL and SECAM — 25 staff / with. Speed of change of the staff also less or is equal digital video of the listed formats 30 staff / with, however the sanction of the imageseldom exceeds 320 x 240 пикселов. At these parameters speed of receipt of the information makes about 6 Mb per second and the processor has time to execute her(it) декомпрессию and transfer on the Bus in videomemory. However such size of the image is too small for comfortable viewing on the screen, therefore it(him) usually scale on all screen. In this case speed of the dataflow grows up to tens and hundreds megabytes a second. This circumstance has led to to occurrence of videoaccelerators which are able to scale independently video in formats AVI and MPEG-1 on all screen, and also to carry out smoothing отмасштабированного images that it did not look as a set квадратиков. The overwhelming majority of modern 2D-accelerators the some people are at the same time and videoaccelerators, and, for example ATI Rage128, are able to reproduce and video in format MPEG-2 (i.e. with the initial sanction 720 х 480).

To multimedia - functions also carry a hardware digital compression and декомпрессию video (that does not meet almost on mass videomaps), presence композитного a video output, a conclusion of a TV-signal to the monitor, a low-frequency video input and a high-frequency TV-input, the module for job with a teletext and other functions.

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