ALGOL W is a relatively simple upgrade of the original ALGOL 60, adding string, bitstring, complex number and reference to record data types and call-by-result passing of parameters, introducing the while statement, replacing switch with the case statement, and generally tightening up the language.
[1] With a number of small additions, this eventually became ALGOL W. Wirth supervised a high quality implementation for the IBM System/360 at Stanford University that was widely distributed.
[2][3] The implementation was written in PL360, an ALGOL-like assembly language designed by Wirth.
The key differences are improvements to record handling in Pascal, and, oddly, the loss of ALGOL W's ability to define the length of an array at runtime, which is one of Pascal's most-complained-about features.
ALGOL W's syntax is built on a subset of the EBCDIC character encoding set.