function show_div(div_id) {
    // hide all the divs
    document.getElementById('specs').style.display = 'none';
    document.getElementById('technologies').style.display = 'none';
    document.getElementById('review').style.display = 'none';
    document.getElementById('feedback').style.display = 'none';

    // show the requested div
   if (div_id != null) {
      document.getElementById(div_id).style.display = 'block';
   }
}

function show_all() {
    // show all the divs
    document.getElementById('specs').style.display = 'block';
    document.getElementById('technologies').style.display = 'block';
    document.getElementById('review').style.display = 'block';
    document.getElementById('feedback').style.display = 'block';

}

window.onload = show_div;