You can use read as merlyn points out, but you can also do it by setting the input record separator to a scalar reference.

{
  local $/ = \512;

  while (<FILE>) {
    # process the 512 bytes you have in $_
  }
}
[download]

--
<http://www.dave.org.uk>

"Perl makes the fun jobs fun
and the boring jobs bearable" - me