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What happens when a CPU starts

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Re: What happens when a CPU starts

#51

Post by martyvis »

fzliu wrote: post #43

> This is because when the power supply is first powering up, even if it only takes a second or two, the CPU has already received "dirty" power, because the power supply was building up a steady stream of electricity. Digital logic chips like CPUs require precise voltages, and they get confused if they receive something outside their intended voltage range. This is only partially true. When digital chips boot up, gat…

All so called digital devices are really analog devices corralled into operating using binary logic. All it takes is a volt or two applied or removed unexpectedly on those discrete components and you have a bit-flip and possible ensuing mayhem.

Re: What happens when a CPU starts

#54

Post by 8bitsrule »

retrac wrote: post #13
billti wrote: post #3

Amongst the first sentences... > It may be thought of as what happens when a whole computer starts, since the CPU is the center of the computer and the place where the action begins. I thought that too. Last year I spent a while getting as low-level as I could and trying to understand how to write a boot loader, a kernel, learn about clocks and pins and interrupts, etc. I thought, "I know, I'll get a Raspberry Pi! Th…

As early as the mid-70s, minicomputers started including microcontrollers to manage the boot environment. I had a Sun machine once that included what they called Lights Out Management. A little microcontroller that had control over the system power and etc. Always available via its dedicated serial port, even when the machine was shut off. Everything is like that now. A smartphone will have multiple processors. Some…

True. It's like what's happened with electronics, radio, video in that way. A solid grasp of the (always-present) basic components, and basic tech and design philosophy, goes a long way. It's like learning a language.

So easily-understandable articles like this are essential for beginners, along with a short list of masterful books ( e.g. those by Forrest Mims, for electronics) and playing with physical components! The rest is the endless variations, but they're all speaking that language, 'cuz the laws don't change.

Re: What happens when a CPU starts

#57

Post by Dylan16807 »

hhh wrote: post #39
tmtvl wrote: post #37

Earlier quoted context omitted.

writing programs for old game consoles, Oh yeah, like the Intellivision. particularly the Nintendo DS. Oh come on, the DS ain't that old.

20 years next year.

It did launch in 04/05, but it's only two console generations older than a switch.

Re: What happens when a CPU starts

#58

Post by TedDoesntTalk »

toast0 wrote: post #48
MuffinFlavored wrote: post #44

Earlier quoted context omitted.

> In a typical Windows 10 installation with many background processes and services, the CPU context switching rate can vary greatly depending on the specific system's hardware configuration, running processes, and workload. However, on a typical system, the context switching rate can be anywhere from a few hundred to a few thousand times per second. Would you agree with this statement from ChatGPT? Is the Windows ker…

Yeah, more or less; mostly more. pusha/pushad is one of those instructions that sounded good, but isn't used much (it became invalid in amd64), windows will push the registers one at a time, and maybe FPU, MMX, SSE, etc registers; of course, that's a lot of extra pushing, so there's strategies to avoid it if the thread doesn't use them. If you switch to a different task, you're going to need to load its page tables,…

This seems wildly inefficient. Can’t we have multiple sets of registers? Not millions, but…

Are registers expensive in hardware? Why not have loads of them?

Re: What happens when a CPU starts

#59

Post by dreamcompiler »

alexeldeib wrote: post #33
Rimintil wrote: post #16

> The memory chips respond by sending the contents of the selected memory cell over the data bus to the CPU. What does that ROM memory cell _physically look like_? How do we physically manipulate it to contain a 1 or a 0 (absence of something)?

A peer mentioned different types of memory and flip flops. I’d search for JK flip flop or D flip flop/latch for conceptual pointers. Those can be used to build up register files. The logic gates used to build flip flops/latches use things like NMOS/CMOS/PMOS - different kind of metal oxide seniconductor logic based on substrate. The differing behavior affects how you arrange circuits (voltage source, ground, etc) to…

The standard decomposition is

--The instruction set is the lowest level of user-visible software. The instruction set is implemented (in principle) by microcode.

--Microcode (if present) is a bunch of hardwired logic signals that cause data to move between subunits of the CPU in response to instructions. Register transfer specifications govern the design at this level.

--A CPU is a collection of subunits including registers, arithmetic units, and logic gates.

--Registers are collections of flip-flops.

--Arithmetic units are made of logic gates.

--Flip-flops are made from logic gates in feedback configurations to make them stateful. State machine theory governs the design of these circuits.

--Logic gates are stateless and made of transistors. Boolean algebra governs the design at this level.

--Transistors are made of NMOS or PMOS or bipolar silicon junctions. Device physics and electrical properties govern this level.

This abstraction hierarchy is useful when learning, but in the real world the abstraction layers are much blurrier: Everything's really just transistors, stateless stuff often has invisible state, electrical considerations matter at every level, etc.

Re: What happens when a CPU starts

#60

Post by TedDoesntTalk »

kens wrote: post #42

If anyone is interested in what happens with an older CPU, I've written up how the IBM 1401 from 1959 starts up: https://www.righto.com/2021/02/an-ibm-1401-mainframe-compute... Among other things, since it uses magnetic core memory, you can run the program that was loaded when you shut it off.

Go Ken!
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