With MBR (master boot record) partitioning, Windows had to be on a primary partition, and it was only possible to have four of them. Linux could be installed to

With MBR (master boot record) partitioning, Windows had to be on a primary partition, and it was only possible to have four of them. Linux could be installed to a primary or extended partition, of which there could be more. As far as I know the order never actually mattered as long as Windows could have a primary partition. The newer GPT system doesn't have such a distinction or low limits (Windows is limited to 128 partitions per disk; I think Linux can handle more).