第5章アルゴリズムのハードウェアによる実現：コンピューターシステム設計

Read this concise history of computers starting from the nineteenth century (https://openstax.org/r/ 76CompHistory19) to see how computers have changed and been developed over time.

The job of input/output (I/O) devices is to take input from a user (i.e., typing on a keyboard or speaking into a microphone), transform it into 1s and 0s, and store this information in memory. It also takes some 1s and 0s, generated by some type of software program, from memory and translates them to an output format such as a picture on the screen or a sound from a speaker. Distinct devices have different speeds and varying ways of transforming the input and output to/from 1s and 0s.

Any I/O device, your keyboard for example, connects to the computer system using an interface such as a USB port that we see in all computers. The USB controller shown in Figure 5.4 is the piece of hardware that manages the USB port and allows it to detect that a device has been connected. Another important piece of hardware is the main memory.

For the CPU to execute programs and process data stored locally, it needs to obtain them from the computer's disk. But a disk is very slow. So, the CPU brings what it needs from the disk and temporarily stores it in faster storage referred to as main memory or random access memory (RAM). When you buy a laptop, one of the specifications is the amount of memory it has, such as 16 GB of RAM or 32 GB of RAM. The main memory is much faster than the disk and connected to the CPU with a faster interconnect, as shown in Figure 5.4. When you click an icon to start a program (e.g., your web browser), the program and its needed data are copied from the disk to the main memory. Then, the CPU reads the data and instructions from the memory into the CPU’s registers and the ALU starts executing it.

The processor, also called the microprocessor, is another name for the CPU. It is the brain of the computer system, and its main job is to execute programs. As we discussed earlier, the processor fetches instructions from the memory, understands what each instruction wants to do, gets the data needed to execute the instruction, executes the instruction, and then stores the result in a register or in the main memory. It keeps doing so until the program ends. There have been huge advances in processor design leading to faster and more powerful computers. The processor in your smartphone today is more powerful than a big supercomputer was a few decades ago.