LAPACK routines are written so that as much as possible of the computation is performed by calls to the Basic Linear Algebra Subprograms (BLAS)  . Highly efficient machine-specific implementations of the BLAS are available for many modern high-performance computers. The BLAS enable LAPACK routines to achieve high performance with portable code. The methodology for constructing LAPACK routines in terms of calls to the BLAS is described in Chapter 3.
The BLAS are not strictly speaking part of LAPACK, but Fortran 77 code for the BLAS is distributed with LAPACK, or can be obtained separately from netlib (see below). This code constitutes the ``model implementation'' .
The model implementation is not expected to perform as well as a specially tuned implementation on most high-performance computers - on some machines it may give much worse performance - but it allows users to run LAPACK codes on machines that do not offer any other implementation of the BLAS.