1 : Strobe
2 : Data 0
3 : Data 1
4 : Data 2
5 : Data 3
6 : Data 4
7 : Data 5
8 : Data 6
9 : Data 7
10 : Acknowledge
11 : Busy
12 : Paper Empty
13 : Select
14 : Auto Feed
15 : Error
16 : Init
17 : Select In
18 - 25 : ground

D0 - D8 are 8 ouputs which we will use in a lot of our projects . These are TTL level output pins which means a logic 1 is equivalent to 5v and a logic 0 is 0v , in real life this is rarely the case and when a load is attached this may change . The parallel port can only source a couple of milliamps , so it is suitable for leds and some of other interfacing but for higher power devices you need driver circuitry such as transistors .