let me see if I can explain:
Memory bus: The memory bus is made up of two parts: the data bus and the address bus. When people just make reference to "the memory bus" they are usually referring to the data bus, which carries actual memory data within the PC. The address bus is used to select the memory address that the data will come from or go to on a read or write.
The wider the data part of the bus, the more information that can be transmitted simultaneously. Wider data buses generally mean higher performance. The speed of the bus is dictated by the system clock speed and is the other main driver of bus performance. The bandwidth of the data bus is how much information can flow through it, and is a function of the bus width (in bits) and its speed (in MHz).
Therefore, 256bit is better than 128bit and 64bit gives the lowest performance.
DVI: Short for Digital Visual Interface, a digital interface standard created by the Digital Display Working Group (DDWG) to convert analog signals into digital signals to accommodate both analog and digital monitors. Data is transmitted using the transition minimized differential signaling (TMDS) protocol, providing a digital signal from the PC's graphics subsystem to the display. The standard specifies a single plug and connector that encompass both the new digital and legacy VGA interfaces, as well as a digital-only plug connector. DVI handles bandwidths in excess of 160 MHz and thus supports UXGA and HDTV with a single set of links. Higher resolutions can be supported with a dual set of links.
IF u have a highend tv/monitor such as LCD, PLASMA etc. then u can use DVI interface. Else for normal tv, connect using the s-video output if available.