The Decoder.GetChars(Byte[], int, int, Char[], int) method converts sequential blocks of bytes into sequential blocks of characters, in a manner similar to the ASCIIEncoding.GetChars(Byte[], int, int, Char[], int) method of this class. However, a System.Text.Decoder maintains state information between calls so it can correctly decode byte sequences that span blocks. The System.Text.Decoder also preserves trailing bytes at the end of data blocks and uses the trailing bytes in the next decoding operation. Therefore, ASCIIEncoding.GetDecoder and ASCIIEncoding.GetEncoder are useful for network transmission and file operations, because those operations often deal with blocks of data instead of a complete data stream.