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XMB (Cross Media Bar) is a type of menu in which we navigate in all basic directions, developed by Sony. It's used on PSP, PS3 and some newer Sony Bravia TV's.
Once a category is selected, its options appear below the icon, selectable by pressing right on the directional pad. Going back is possible by pressing the left directional button or the Circle button (for European and American version), or X button (Asian versions only). Some items have an option menu that can be displayed by pressing the Triangle button. The XMB is capable of limited multitasking. This is accessed by pushing the "Home" button while listening music, looking at photos, etc. This feature can be used to watch a video, look at a certain photo, listen to music, and look at the current web page, all while browsing the XMB. However, what is in the background will be cancelled if any item is accessed on the XMB. The background color on the XMB changes color depending on the current month. On a PSP with firmware 2.00+ the background color can be changed or the background can be changed to a picture.
Customizing the XMB
For a detailed guide to install Themes safely visit here.
Unofficial Themes for PSP XMB
On hacked and Custom Firmwares for the PSP, aspects of the XMB can be customized such as the icons, battery and volume meters, the text displayed under each menu item, the animated wave in the background, and the bitmap for each month can be changed. The PSP Slim contains 27 backgrounds, instead of the original 12, varying from color to color. On the original firmware, only the menu icons themselves can be customized via themes.
The XMB on the PSP is known internally as the "VSH" and since the advent of homebrew is highly customizable. The firmware files vshmain.prx and paf.prx contain the main positioning of the icons and the layout of the XMB. Topmenu_plugin.rco contains the menu icons as well as the glow and shadow icons for each menu icons (3.52 and below firmware), and for 3.70 and above firmware, it is named Topmenu_icon.rco. Topmenu_plugin.rco also holds the names of any of the icons in the XMB (on 3.52 and below), and for 3.70 and above it only stores text. System_plugin.rco file stores components such as XMB sounds and the busy icon and system_plugin_fg.rco contains the battery icon. Impose_plugin.rco in the other hand, holds the sound volume icon. Finally, system_plugin_bg.rco contains the background animated wave. Before the firmware update 2.70 was released, it was very easy to edit the menu background colors by just editing the BMP files at FLASH0:/VSH/RESOURCE files 01.bmp to 12.bmp, but after the update all the background BMPs were held in a single BMP file named 01-12.bmp. The files were added after each other in the BMP file by simple HEX editing. That way opening the file in Paint for example, the user would just see the first month background color which is grey.
Official Themes for PSP XMB
PSP users with the 3.70 Official Firmware or newer have the ability to download themes for the Playstation Portable and apply theme to the Playstation Portable without hacking. There is also software that was released by Sony that allows any one person to create a theme.
These "official" themes can only change the looks of the XMB icons, but can not changes other resources, like the XMB wave or the position of the icons.