Using old machines not PXE capable

Yes, computeMode can be used to create a cluster even with quite old machines.

However, those machines often do not provide the PXE boot method.

Etherboot

Hopefully, thank to Etherboot, it is possible to generate a PXE floppy for most of the existing network adaptors using the ROM-O-MATIC.

Then just write the floppy image on a floppy disk, insert the disk into the drive and change to boot order to first try the floppy.

You are all set.

Rq: It is also possible to use a PXE boot from CD or from a USB key for instance.

PXE on a disk

You may also have a look atthe pxe-on-a-disk page, that provides a PXE disk that should boot using any network card by detecting the actual driver to use.