Set sector count for multiple sector I/O on the drive.

Multiple sector mode (aka IDE Block Mode), is a feature of most modern IDE hard drives, permitting the transfer of multiple sectors per I/O interrupt, rather than the usual one sector per interrupt.

When this feature is enabled, it typically reduces operating system overhead for disk I/O by 30-50%. On many systems, it also provides increased data throughput of anywhere from 5% to 50%. Some drives, however (most notably the WD Caviar series), seem to run slower with multiple mode enabled. Your mileage may vary.

Most drives support the minimum settings of 2, 4, 8, or 16 (sectors). Larger settings may also be possible, depending on the drive. A setting of 16 or 32 seems optimal on many systems.

Western Digital recommends lower settings of 4 to 8 on many of their drives, due tiny (32kB) drive buffers and non-optimized buffering algorithms.

Some drives claim to support multiple mode, but lose data at some settings.
Under rare circumstances, such failures can result in massive filesystem corruption.