What exactly is SL controller

Dear Experts,

when installing SAP, both sapinst and its "new" version, the Software Provisioning Manager,

are asking for a media, called again Kernel, or a.k.a. SL controller.

It contains the same directory as the kernel itself and even issues a warning, when one tries

to unpack it to the same directory, where the kernel already is unpacked.

So, I was wondering...

1) Why 2 kernels ?

2) What exactly is SL controller ?

3) I also noticed, that SWPM 7.20 accepts SL controller 7.00, but there is also SL controller 7.20 available for download...

Please kindly try to bring light into this, I tried to google, but nobody explained it nowhere...

It's like a big common secret - everybody knows about it, but nobody dears to speak about it :-D

Thanks a lot for the replies!