Multiple buffering

It is also used to avoid the need to use dual-ported RAM (DPRAM) when the readers and writers are different devices.

After the initial transient where W1 fires alone, this system is periodic and the transitions are enabled – always in pairs (R1 with W2 and R2 with W1 respectively).

In addition, computer monitors constantly redraw the visible video page (traditionally at around 60 times a second), so even a perfect update may be visible momentarily as a horizontal divider between the "new" image and the un-redrawn "old" image, known as tearing.

When all drawing operations are considered complete, the whole region (or only the changed portion) is copied into the video RAM (the "front buffer"); this copying is usually synchronized with the monitor's raster beam in order to avoid tearing.

The page-flip is much faster than copying the data and can guarantee that tearing will not be seen as long as the pages are switched over during the monitor's vertical blanking interval—the blank period when no video data is being drawn.

Finally, the displayed image was started without waiting for synchronization and thus with minimum lag.

[1] Due to the software algorithm not polling the graphics hardware for monitor refresh events, the algorithm may continuously draw additional frames as fast as the hardware can render them.

The term double buffering is used for copying data between two buffers for direct memory access (DMA) transfers, not for enhancing performance, but to meet specific addressing requirements of a device (esp.

[5] DOS and Windows device drivers are a place where the term "double buffering" is likely to be used.

Double buffering is also used as a technique to facilitate interlacing or deinterlacing of video signals.

Sets 1 , 2 and 3 represent the operation of single, double and triple buffering, respectively, with vertical synchronization (vsync) enabled. In each graph, time flows from left to right. Note that 3 shows a swap chain with three buffers; the original definition of triple buffering would throw away frame C as soon as frame D finished, and start drawing frame E into buffer 1 with no delay. Set 4 shows what happens when a frame (B, in this case) takes longer than normal to draw. In this case, a frame update is missed. In time-sensitive implementations such as video playback, the whole frame may be dropped. With a three-buffer swap chain in set 5 , drawing of frame B can start without having to wait for frame A to be copied to video memory, reducing the chance of a delayed frame missing its vertical retrace.
Double Buffering Petri Net