About the DRTM Data SRTM linked above (Readme.txt) ROCESSED SRTM DATA VERSION 4
The data distributed here are in ARC GRID, ARC ASCII and Geotiff format, in decimal degrees and datum WGS84. They are derived from the USGS/NASA SRTM data. CIAT have processed this data to provide seamless continuous topography surfaces. Areas with regions of no data in the original SRTM data have been filled using interpolation methods described by Reuter et al. (2007).
Here are the links of SRTM data in ASCII format of Indonesia coverage. The total size of files is about 300 MB
The tutorial of SRTM data processing and analysis will be republished soon.