<Original Answer> because some devices on the board are slower than others and do not require or cannot support the same bus speeds.
<Update> The book that this question comes from has another answer: that it is required for backwards compatibility. This is the answer for the test, but, I do not like it.
My answer is that having a high speed bus to some devices is a waste of CPU effort that could be better used on RAM or other high-speed items. There is not point to putting a modem or printer on a high speed bus that the CPU has to monitor only to find out that the printer or modem is done with the last burst of data sent.
This started with the limitations of the earlier PCs. The 8088 CPU in the original IBM PC-XT ran at 4.77 MHz, and at the time, so did the 8-bit ISA bus, and the PC-AT operated at 6-8 MHz. Anyway, the peripherals available were designed to operate at those speeds, and everything was tied to the system clock and changing it to change the CPU speed would have consequences on everything.
Then came the early PC clones. They sped up the CPU and might have used faster memory, but kept the peripheral bus and other timings at the original speeds. That way, existing peripherals on the market and existing memory could be used. So they sped up what they could and still have compatibility, and kept other components like the peripheral bus, keyboard, and so on at the same speed for compatibility.
Then as time went on, the CPU kept getting faster than the motherboard could handle and keep all the timings unified, so that was where multipliers and all were introduced. So a 66 MHz CPU was still clocking the motherboard at 33 MHz, and and peripheral bus at 16 or 33 MHz depending on the type of interface.
As chipsets got faster, they still could not keep up with the CPU. So an Athlon-64 CPU may be clocked at 2-3 Ghz, but the communication from the CPU to the Northbridge of the chipset can only go at about 1 GHz. The buses got faster with time, but still cannot keep up with the CPU, and now, CPUs are multi-core, hyperthreaded, and so on.
because some devices on the board are slower then others , and do not require or can not support the same bus speeds
To support a number of processors and memory that differ in bus speed.
to support a number of processors and memory..
that differ in bus speed
It makes compatible with low price memory and result wider market for the motherboard itself.
yes
Yes, you can have as many as your case and motherboard will support.
No.
The faster the CPU can push data around the motherboard is mesured as a frequency
The Asus motherboard 77-12dl will be more than enough for your tpical home setup.
Yes.
Because the motherboard/processor is designed with that speed in mind, so overheating and various other issues can occur much more frequently at higher speeds. Also, the process of running hardware at a higher speed than is standard is called overclocking.
A server mother is like a normal motherboard except they are geared to a server processor and can hold more than one processor usually. They also support ECC memory which is memory with error correction. They support RAID. And most can are slim to be put in what is called a U1 chassis so they can go on a server rack.
The processor size or speed does not determine how much RAM your system needs. Generally speaking, the newer the system, the more RAM you can add. The amount of RAM slots on a motherboard and the motherboard's own subsystem (the BIOS) will determine how much RAM you can add to a particular motherboard.
You can buy more RAM for your computer. It can speed up your computer depending on your memory usage. You can buy it at a local electronics store. RAM only improves a computer's speed to a certain point, at which motherboard components and processor speed limit computer performance. So the question is oversimplified as computer speed is governed by motherboard chipsets, processor core numbers and speed, RAM volume, hard drive writing speed, etc.
It depends on your motherboard. It likely uses either DDR or DDR2 memory, and the speeds that are supported vary by the make and model of your motherboard. It doesn't support more than 4gb of RAM.