Breaking down In/Out abbreviated is I/O. The I/O bus includes communications (serial) ports, parallel (printer) port, keyboard port, and today Universal Serial Bus (USB). The I/O bus is the slowest of the bus system in the PC today. For those of you wondering why not just make everything fast? The simple answer is, "Speed costs. How fast do you want to go?" It would be money wasted to create a PC where someone could type at a million words a minute.
If you are wise to the ways of the PC, you may be wondering what about data bus and address bus? These two buses are discussed in Chapter 0011.
Just a few paragraphs ago, in Backside bus, a reference was made to a special type of RAM. It is time to flip to the backside and see what is happening back there.
The original IBM 5150 had one thing in common with the other PCs of the day. They were all excruciating slow. As the components got quicker, some parts became more capable then other parts. This observation became one of Tcat's laws of Engineering. "All computers wait at the same speed".
This was not good for Intel. Who would purchase a new, faster CPU if it had to wait for something to do?
By analysis of how a computer works, it was found that, in general, if a CPU needed a piece of information now, there is a high likelihood it will be needed again, real soon. So, if the CPU designers created an intelligent process to determine what might be needed again soon, they could put that data in super high-speed memory. By limiting the amount of super-high speed memory, they could keep costs low, to only one or two limbs (say one arm and a leg), yet improve the working time of the CPU. That is the concept known as cache.
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