Here’s the deal: I wanted to be able to temporarily see all the posts at once in the WordPress Administration, so I went into the
wp-admin folder, and poked around, and became frustrated: it wasn’t that simple!
/wp-admin/includes/post.php and scroll to line 517. You will see
posts_per_page value to whatever you want it to be. Note: deleting the code will not let you view all posts.
WARNING: I don’t ever like to modify the default WordPress files, because when they get updated, you’ll be screwed. This is a only a temporary fix. It will not last if you update WordPress.