2. The Context of Cybersecurity: Cyberspace 19 hacker is able to input valid machine instructions into memory and then prompt the CPU to execute them, he can hijack the operation of a computer! Figure 2.6 Computer memory is similar to post office boxes—the only cell with a value shown is at address 0x42. In order for a program to be run, its instructions and data must be loaded into memory. Memory is constantly being written, read, and re-written. Computers work off of data in memory because unlike storage, it is close to the CPU and is able to be accessed quickly. Memory is volatile, meaning that when a computer is turned off, all the contents of memory are lost. Therefore, data in memory must be written to storage in order for it to be saved. A typical laptop computer might come with anywhere from four to thirty-two GBs of memory (i.e., RAM). As we have seen, all of the information processed by a computer is a string of 1s and 0s. This includes memory addresses, instructions that “tell the CPU what to do,” and user data, such as documents, videos, and pictures. The general purpose nature of a computer is due to its ability to interpret strings of 1s and 0s differently based on context. Sometimes the 1s and 0s select wires to read or write a value to a memory address, sometimes they cause the CPU to perform an operation, sometimes they instruct a monitor how to render pixels on a computer screen, etc. 2.2.2 Storage Storage is where computers store data persistently. All of a computer’s programs and data, including the operating system, reside in storage. Storage is inexpensive compared to memory and is also much slower. It is needed because data held in storage is saved
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