DVD data is read from an optical disc. Double buffering is used for outer error
correction syndromes, the syndrome for one ECC frame being accumulated in one syndrome
buffer, while error correction calculations for preceding data block are performed
using a syndrome accumulated previously in another syndrome buffer). The syndrome
buffers are used in alternating fashion as further blocks of data are received,
while the flow of data to a main buffer is uninterrupted. This reduces buffering
requirements in the decoder, and relaxes time constraints on the error correction
calculations. A multi-beam implementation is disclosed, providing higher throughput.
