In other words, if your sister's drive is master on an IDE channel and is the only drive on that channel, set it to Master. If it is on an IDE channel with another drive present and that other drive is Master, then set your sister's drive to Slave. If it is on an IDE channel with another drive present and that other drive is Slave, set your sister's drive to Slave Present (which will also make your sister's drive Master).
For the specific configuration you describe:
dodecahedron wrote:f i want the hard drive to be a master with a second drive on the same IDE channel, should i leave it as Master or change to Slave Present ?
You should change it to Slave Present.
I actually ran into this problem at work just this past Friday. The other IBM Deskstar hard drive in my RAID 1 mirror failed and I had to replace it (if you recall its twin failed about three months ago - both are just past the three year warranty expiration, so apparently the built-in auto-fail timer worked as designed
). I ended up replacing it with a Western Digital 80 GByte drive.
Unfortunately the BIOS didn't recognize the replacement drive on boot. After a little investigation I found that the reason was that the drive had been set to Slave Present (actually labeled "Master with Slave Present") to match it to the system from which it had been removed but on my system it was the only drive on the channel and should have been set to plain Master. When I checked the jumpers on first installing it I saw "Master" and didn't bother reading the rest about "Slave Present", which is why I got the setting wrong.
Honestly, I didn't even think to check for a Slave Present setting. In fact I was quite surprised to see a Slave Present setting on an 80 GByte drive. I thought they dropped that years ago.