RAM中数据与程序指令的存储位置有何区别？

Hey there! Let's unpack your questions step by step—this low-level computer stuff can feel overwhelming at first, but once you connect the dots it makes a lot of sense.

RAM: Where do program instructions and data live? #

First off: Yes, program instructions do get stored in RAM (for most modern general-purpose computers, anyway). Here's the breakdown:

• RAM uses a unified address space—meaning both instructions and data are stored in the same pool of memory, just at different memory addresses. There's no physical "wall" separating them.
• The CPU uses its Program Counter (PC) register to keep track of which instruction to fetch next. When the CPU is in "fetch" mode, it grabs the binary instruction from the RAM address pointed to by the PC, then increments the PC to the next instruction.
• When the CPU needs to work with data (like numbers, text, or variables), it uses load/store instructions to pull data from specific RAM addresses into its internal registers, or write data back from registers to RAM.

For example: When you open a web browser, the browser's executable code (instructions) gets loaded from your hard drive into RAM, and all the data it uses (like the webpage you're viewing) also lives in RAM while the browser is running.

What's ROM, anyway? #

ROM stands for Read-Only Memory—a type of non-volatile storage (meaning it keeps its data even when power is turned off). Unlike RAM, you can't easily write to ROM (or in some older cases, not at all).

• Its main job is to hold critical boot-up instructions. When you turn on your computer, the CPU doesn't have any instructions in RAM yet (RAM is empty when powered off). So it starts by executing the firmware stored in ROM (like the old BIOS or modern UEFI).
• This firmware initializes your hardware (CPU, GPU, hard drive, etc.), then loads the operating system from your hard drive/SSD into RAM. Once the OS is in RAM, the CPU switches to executing instructions from RAM, and ROM's job is basically done until the next boot.
• Modern devices often use flash memory (a type of rewritable non-volatile storage) instead of traditional ROM, but it's still referred to in the same context because it serves the same boot-up purpose.

Does the CPU get everything from registers? #

Nope—registers are just tiny, super-fast storage inside the CPU (we're talking a few dozen 64-bit registers on modern x86/ARM chips). They're only used for holding data or instructions that the CPU is actively working on right now.

• Here's the typical flow:
  1. The CPU fetches an instruction from RAM (or L1/L2/L3 cache, which is faster intermediate storage between RAM and the CPU) into its Instruction Register.
  2. It decodes the instruction to figure out what to do.
  3. If the instruction needs data, the CPU first checks if that data is in cache. If not, it loads the data from RAM into a general-purpose register.
  4. The CPU performs the operation (like adding two numbers) using the registers.
  5. If needed, it writes the result back from the register to RAM (or cache).

Registers are like the CPU's "workbench"—they hold the tools and materials it's using right this second, but all the raw materials (program instructions, large datasets) live in RAM or other storage until needed.

内容的提问来源于stack exchange，提问作者maxbd