Stanford’s Apple Collection, the largest assembly of Apple Co. historical materials, can help historians, entrepreneurs and policymakers understand how a startup launched in a Silicon Valley garage became a global technology giant. “Through this one collection you can trace out the evolution of the personal computer,’’ said Stanford historian Leslie Berlin. “These sorts of documents are as close as you get to the unmediated story of what really happened.’’ The collection is stored in hundreds of boxes taking up more than 600 feet of shelf space at the Stanford’s off-campus storage facility.