The LZ-77 compression method is an adaptive compression method where the encoder dynamically builds a dictionary from the input data and then uses the previously occurring strings to compare and compress the new strings.

The amount of compression i.e. the compression ratio depends on :

• Length of the dictionary

• Size of the window used

The encoder maintains a window and shifts the input to that window from right to left as the symbols are being encoded and that is why this method is called sliding window.

The sliding window has two parts:

• The left part is called the search buffer and it contains the current dictionary. It includes the strings that have been input and encoded.

• The right part of the window is called the look ahead buffer and it contains the strings which are to be encoded.

The drawback of this method is that it assumes that a match is found around the window which is not the case in practical applications.

Compression ratio can be improved only by increasing the size of search window which increases the latency.

This method is not practically applicable as there is no definite data structure.