Prediction by partial matching, or PPM, is a finite­ context statistical modeling technique that can be viewed as blending together several fixed­ order context models to predict the next character in the input sequence. Prediction probabilities for each context in the model are calculated from frequency counts which are updated adaptively and the symbol that actually occurs is encoded relative to its predicted distribution using arithmetic coding. The maximum context length is a fixed constant, and it has been found that increasing it beyond about six or so does not generally improve compression. -Prediction by partial matching, or PPM. is a finite