<dd>Pointer to the first item of the <em>byte array</em> to be written. The size of data to be written is sector size * <ttclass="arg">count</tt> bytes.</dd>
<p>The specified memory address is not that always aligned to word boundary because the argument is defined as <tt>BYTE*</tt>. For more information, refer to the description of <ahref="dread.html"><tt>disk_read</tt></a> function.</p>
<p>Generally, a multiple sector transfer request must not be split into single sector transactions to the storage device, or the write throughput will be drastically decreased.</p>
<p>FatFs expects delayed write function of the disk control layer. The write operation to the media does not need to be completed at return from this function by what write operation is in progress or data is only stored into the write-back cache. But write data on the <ttclass="arg">buff</tt> is invalid after return from this function. The write completion request is done by <tt>CTRL_SYNC</tt> command of <tt><ahref="dioctl.html">disk_ioctl</a></tt> function. Therefore, if a delayed write function is implemented, the write throughput of the filesystem will be improved.</p>
<p><em>Remarks: Application program MUST NOT call this function, or FAT structure on the volume can be collapsed.</em></p>