What Is the "Root" of a PSP Memory Stick?

The PSP doesn't expose a hierarchical "root directory" to the user. The Memory Stick PRO Duo is formatted FAT32 and presents a flat top-level view when accessed via USB or the XMB.

What You See (Top Level = "Root")

ms0:/ (or "Memory Stick" on PC)
├── PSP/
│   ├── GAME/       ← Homebrew, emulators, signed apps
│   ├── GAME150/    ← 1.50 kernel homebrew (legacy)
│   ├── SAVEDATA/   ← Game saves (ULJS00000, etc.)
│   ├── SYSTEM/     ← Browser bookmarks, network config
│   ├── THEME/      ← .ptf themes
│   ├── MUSIC/      ← .mp3, .at3 (ATRAC)
│   ├── VIDEO/      ← .mp4, .avi (PSP format)
│   ├── PICTURE/    ← .jpg, .png, .gif
│   ├── COMMON/     ← Shared data (e.g., PS1 saves)
│   └── UPDATE/     ← EBOOT.PBP for firmware install
├── ISO/            ← CFW: Game ISOs/CSOs here (or /PSP/ISO)
├── SEPLUGINS/      ← CFW: .prx plugins + game.txt/pops.txt/vsh.txt
└── ... (any user folders)

Key Points

• No "C:\" or "/" prompt. The PSP OS abstracts the filesystem. You navigate folders in XMB (Photo, Music, Video, Game).
• Homebrew expects ms0:/PSP/GAME/APPNAME/EBOOT.PBP. That's the "root" for that app.
• On PC (USB Mode): The drive letter is the root. Drag folders there.
• CFW Note: seplugins folder at root loads plugins at boot (vsh.txt = XMB, game.txt = in-game, pops.txt = PS1).

So: "Root" = the drive letter on PC, or the top folder list in a PSP file manager (IRShell, VitaShell, PSP Filer).