When you press the shutter button, and take an image, a DSLR camera's sensor is exposed to light, and the sensor captures image data. This data is then processed in the camera, and written to the storage card.
To help speed up this process, DSLRs contain a camera buffer (consisting of random access memory, or RAM), which temporarily holds the data information before the camera writes it to the storage card. The camera buffer speeds up the time between shots and allows for continuous (burst) shooting mode. This mode refers to the camera's ability to take several shots immediately after one another. The number of shots that can be taken simultaneously depends on the size of the camera's buffer.
Most modern DSLRs contain large buffers that allow you to keep shooting while data is processed in the background. Original DSLRs didn't contain buffers at all, and you had to wait for each shot to be processed before you could shoot again!
The camera buffer can be located either before or after image processing.
- Before Image Processing Buffer. The RAW data from the sensor is placed directly into the buffer. The data is then processed and written to the storage card in conjunction with other tasks. In cameras with this sort of buffer, continuous shooting cannot be increased by reducing the file size.
- After Image Processing Buffer. The images are processed and turned into their final format before being placed in the buffer. Because of this, the number of shots taken in continuous shooting mode can be increased by reducing the image file size.
Some DSLRs are now using "Smart" buffering. This method combines elements of both before and after buffers. The unprocessed files are stored in the camera buffer to allow for a higher "frames per second" (fps) rate. They are then processed into their final format and sent back to the buffer. The files later can be written to the storage cards at the same time as images are being processed, thus preventing a bottleneck.