What kind of Memory Stick can I use with my Sony PSP?

I'm also a bit confused by the many different names of Sony memory devices, actually. According to the Sony PSP manual, all of the following types of memory sticks will work with the device:

• Memory Stick Duo
• MagicGate Memory Stick Duo
• Memory Stick Duo (MagicGate / High Speed data-transfer compatible)
• Memory Stick PRO Duo

Sony generally talks about the "Memory Stick", but it encompasses all four of those formats.

Oh, and did I mention that they're different sizes too?

Here's a picture that shows the Memory Stick PRO Duo from Sony and the Memory Stick adapter so you can get a sense of the relative sizes:

Wondering about what MagicGate is all about? It turns out it's a copy protection mechanism. Here's what Wikipedia says about it:

"MagicGate is a copy-protection technology introduced by Sony in 1999 as part of the SDMI. It works by encrypting the content on the device and using MagicGate chips in both the storage device and reader to enforce control over how files are copied."

Having said all that, I still recommend you stick with Memory Stick PRO Duo devices are explicitly indicate that they're Sony PSP compatible. I have heard of some reports of problems with devices that weren't specifically indicated to be PSP compatible...

Hope that helps clear things up!