The Encoder.GetBytes(Char[], int, int, Byte[], int, bool) method converts sequential blocks of characters into sequential blocks of bytes, in a manner similar to the ASCIIEncoding.GetBytes(string, int, int, Byte[], int) method of this class. However, an System.Text.Encoder maintains state information between calls so it can correctly encode character sequences that span blocks. The System.Text.Encoder also preserves trailing characters at the end of data blocks and uses the trailing characters in the next encoding operation. For example, a data block might end with an unmatched high surrogate, and the matching low surrogate might be in the next data block. 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.