Actually, that isn't a sidewinder game pad. It's actually a Microsoft Plug & Play Game Pad. The sidewinder game pad has six main buttons (abc,xyz), two shoulders, a shift button, a start button, and a d-pad. It also has a mode button to control its pass-through game port.

The sidewinder game pad was one of the first digital-only game port pads (The other was gravis's GRIP system, which started off as a multitap, and ended up incorperated into their joysticks, and Xterminator pads). Its big feature was that it had loads of buttons (conventional pads could only have four at the time), and that it could daisy chain to attach up to four pads to the same game port.

Microsoft deliberately kneecapped the pads' DOS support in order to pimp DirectX. It worked. Initially there was no DOS support at all, but later the drivers emulated a 6 button pad, or a pair of two button pads, depending how many were plugged in. The other buttons could be mapped to keys or macros. But only in a windows dos box. The gamepad's protocol has now been reverse-engineered, and they are natively supported in such dos programs as ZSNES, Callus, Genecyst and Sneskey.

Interestingly enough, if you crack open one of these pads, you'll find on the board pre-drilled, pre-stripped solder points for every button on the pad. Suggests to me that the board designers had no idea what the pad would look like, and were keeping their options open. Whatever the reason, this makes the controller boards ideal for arcade controllers- Easy construction, built-in multitap, and keyboard emulation. Lovely.