Some Assembly Required: An approachable introduction to assembly

googles Intel CPU data sheet

Ah, here we go.

https://www.intel.com/content/www/us/en/products/docs/proces...

Just two volumes and 1000 pages of reading. Simple!

You see the machine executing a sequence of instructions, and that is exactly what happens - eventually.

But behind the scenes, the goal of the hardware is to execute those instructions as quickly as possible. Since there's a limit to how fast silicon can work, the way to achieve this is via a number of tricks that effectively throw yet more circuitry at the problem, taking you from millions to billions of transistors.

Just one of these tricks for example is caching. Instead of writing directly to memory (as it appears to your assembler code), the CPU actually writes data to the L1 cache, a smaller but much faster block of memory on the CPU itself. At a later time, the data can be transferred from the cache out to RAM. In fact a modern CPU will have caches feeding into caches - e.g. CPU feeds into the L1 cache, which itself feeds into the L2 cache, then into the L3 cache, and finally into RAM. At each step, the cache gets larger and slower - so while the L1 cache is measured in KB, the L3 cache in a modern CPU might be up to 64MB in size.

You don't see any of this when you are writing assembler code. To all intents and purposes the caches are invisible to you. There are obscure instructions like CLFLUSH that provide very limited control of the cache but these are not typically something you'd use.

It's easy to see how managing these caches enormously increases the circuitry in the chip, without any need for you, the assembler programmer, to even think about them.

As other commenters have noted, other areas where extra circuitry is thrown at the problem include area is pipelining. In your mental model, the CPU is probably plodding along executing instructions one after another. In practice the CPU is aggressively trying to reorder those instructions and execute them in parallel as much as possible. This is an incredibly complex process, requiring enormous amounts of circuitry.

TLDR; what you see as a relatively simple CPU instruction set is really an abstraction - behind the scenes is an enormously complex collection of moving parts that break your code down and try and execute it as quickly as possible.