How do computers work the way they do? When does electricity become executable logic and how?

The Pattern On The Stone: The Simple Ideas That Make Computers Work.

Answer by Razvan Baba:

a duplicate question. How does a computer work?

Laptop PC block diagram schematic and basics
note: this diagram is of a fairly old system round 2001-2002, but concepts still apply.

To summarise, all data goes through the CPU. The CPU can queue all this data, order it, compare it, perform arithmetic on it, even use decimal point numbers (floating point in computer terms). the CPU needs to access data later, so it stores it in a primary memory, or RAM (DDR blocks in diagram, centre) in the PC.
Then, the CPU talks with another chip, called graphical processing unit (GPU – integrated in northbridge on diagram), which is another mini-computer on itself nowadays, but is specialised on displaying data on a screen. The GPU receives raw data, and it must convert it into a grid of pixels, each with its own brightness, hue and saturation. If your monitor uses an analogue connector, the videocard has the additional task of converting the digital signal to an analogue one, and it also transfers the colour information into red, green,blue channels, much like older TVs used.
If it has a DVI or HDMI, it simply sends a digital stream, that is further broken down by another chip inside the monitor.

You want to do another operation, but it's impractical to have too much primary memory because it is fast, and very expensive. RAM does not store information when you power down the PC. So you put your information into a less expensive medium/GB called secondary memory. Practically it's a harddrive or a solid state disk in top-end computers.
It is also possible to have a optical disk drive(ODD or CD-ROM as a secondary).
A SSD is very similar to a USB flash drive in how it works, it's all chips and data.
A HDD (1st IDE on diagram, now replaced with SATA) has moving mechanical parts. A motor spins some magnetic disk platters that store data on them in a particular way, a bit similar to CDs, but reacts to magnetism, not lasers. The magnet is in a head, which moves quickly along the platters and reads the data.
This data is sent to a secondary chip found on the motherboard, historically called southbridge(ICH4M on diagram), that manages all peripheral data. Sometimes a secondary memory(ssd/hdd/odd) can request direct memory access, bypassing this southbridge, making for a priority run.
USB devices, sound(AC97 block, below DDR), also go through this southbridge.
The meatier aspects of computers — real world
The PC requires a power supply, which allows the transistors inside the electronics to switch. Given some supply and an input, the logic circuitry will do the operations by itself. Inputs of 0 and 1 are in fact voltage levels. Current computer CPUs use 1.1V as 1 and 0V as 0, but it can be as low as 0.8V.

More common in the consumer electronics field is the 3.3V, but the lower the Voltage, the less power is dissipated, meaning less heat and more efficiency. Automotive logic uses 12V and industrial stuff goes to 24V, because they are less prone to damage and electromagnetic noise.

Logic circuits are possible because of advancement in transistor technology, specifically MOSFETs. 2-6 MOSFETs make a gate, which are simple operations like (AND, OR, NOT, NOT AND – NAND, NOR, EXCLUSIVE OR – XOR). These gates are all manufactured on a silicon wafer that forms the chip (CMOS process), and are tens of thousands times thinner than hair. A chip can total to a billion transistors.

MOSFETs are the equivalent of water taps. You turn on the tap, water flows. Similarly, you provide charge (voltage) to the gate of the transistor, it allows a 'channel' to form and conducts the water (charge) from the source to the drain. the actual physical process is quite complicated, and few engineers bother or need to understand it fully. You may have seen some clever plumbing tricks in your life, and so can MOSFETs be connected to make some clever logical functions.
In addition to the answers there, I also recommend the excellent short book: The Pattern On The Stone: The Simple Ideas That Make Computers Work.

This book also suggests crazy ideas, like making a computer out of water pipes, just for the fun of arguement. It is cool and possible, but highly impractical. Must-have for somebody bonkers about computing.

How do computers work the way they do? When does electricity become executable logic and how?


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