Thanks RichieP for your reply. Still slightly confused! I have looked at the leads on my printer and card reader and the terminal which slots into the usb port appear to have four slots, which I assume goes into four pins in the usb port. If generally on a desktop it will be 6pin why is mine different - unless I can't add up! Your link was slightly dark so I couldn't quite make out the detail but it looked different to my usb port! I always assumed that whatever you bought to connect it to a pc via the usb port, it simply did just that and there was no concern regarding the number of pins in the usb port! You learn something new every day on the Forums and that's what it is all about.
Thanks again for your help.