The description of the cables is really hard to understand for anybody just starting out with DAK, and as the cables are very expensive you cannot afford to buy the wrong one.
I bought the Brotherlink 1 to use mainly with my KH940, it says downloading and uploading and interactive knitting. But then there is the Brotherlink 5 for interactive knitting. Only after I had bought and used the Brotherlink 1 did I really understand the difference in the interactive knitting. One (the Brotherlink 5) works with any machine even non electronic ones, the Brotherlink 1 needs to be connected to the machine and the carriage set to KC (even for knitting only stockinette) in order that the computer can count the rows knitted. Not a big mistake for me, any stick magnet can be attached to carriage and works just the same. But then in the description for the Brotherlink 1 it also mentions PPD/900. Did not really understood what this means. The Brotherlink 3 connects to the PPD for the KH940. Then there is a cartridge link the Brotherlink 4, more expensive than the whole DAK software to be used for machines with cartridge port and a Brotherlink 7 to be used with floppy drives.
To get the patterns from the floppy disks in DAK I started downloading from disk to knitting machine, then uploading to Computer with DAK. Very slow process and lots of unplugging cables especially if the disks were in the 930 format. I later invested in the Brotherlink 7 and could upload all disk patterns really fast to the computer.
Now I think I even understand the PPD problem. There are 4 modes for the PPD and I believe they use different cables (please correct me if I am wrong). Looking at the description again direct download to the cartridge in mode 1 (KH940, several others and KH270) should work only with Brotherlink 3. After talking to 30Knitter, she uses Brotherlink 5 for connection with PPD, did not work for me. But then I thought why not try the Brotherlink 7 cable (that is not supposed to work with PPD), but it did for me in mode 1. I did not try all the other modes. So now I can design a stich pattern and in one step download to cartridge and use the cartridge on the 270. Pretty nice!