Resistors are much less common than capacitors, but they do have some important uses, one is terminating high-speed signal lines to prevent reflections from interfering with the signal. Another is providing "pull ups" or "pull downs" so that a signal goes to a known state when it is not actively driven.
There is also a certain amount of "analog" circuitry such as power supplies which will likely need resistors. One also sometimes sees "zero ohm links" which are sometimes classified as resistors. These are used when a designer wants to allow multiple options for building the board with slightly different connections.
Other answers have explained why resistors and capacitors are needed at all, but have not yet explained why they are on discrete components on the circuit board, external to the integrated circuits. It certainly is possible to fabricate resistors and capacitors as part of ICs. Many ICs today still have some resistors or capacitors fabricated on-chip.
However, resistors and capacitors take up a lot of chip space. IC resistors need to be long. Capacitance is proportional to area. Both components take up valuable chip area that could be used for large numbers of transistors instead.
It is therefore more economical to place these devices external to the IC, as discrete components. If I look at a modern PC mainboard I indeed see lots of capacitors, but very litlle to none at all resistors. The capacitors are part of the power supply circuits, which are not just in the metal box, but also around for instance the main CPU. That power supply is definitely an analog circuit, not a digital one even though this one it is switching.
The capacitors are needed for smoothing, because. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Why do computer circuits tend to have so many resistors and capacitors? Asked 1 year, 6 months ago. Active 1 year, 6 months ago. Viewed 4k times. Matthew Inbox Matthew Inbox 59 1 1 silver badge 2 2 bronze badges.
A modern CPU for example can contain more than 1 billion transistors. Logic levels are even defined as ranges, for example, TTL low is 0V to 0. Even the inductance of traces on a circuit board can affect the circuit. Analog components resistors and caps help deal with these analog effects from the real world. They're common utility parts with many uses, and BTW everything in the real world of circuits is analog No, it's not. Like any other component in a computer, capacitors can fail, and when they do can cause the computer or the component to fail.
When a motherboard capacitor fails the computer will no longer boot. Either the capacitor needs to be replaced or a new motherboard needs to be put in the computer.
The picture below is an example of an ABIT VP6 motherboard with blown capacitors and one example of how a capacitor may fail. The main components are choke coil and capacitor. The original current first flows through the choke coil commonly known as the coil.
Because the coil has an energy storage property, it can initially filter out some high-frequency clutter, and then enter the capacitor bank to further filter, purify and flatten the peak wave is drawn into square wave.
The motherboard must have a stable and pure current supply, which is why most of the capacitors are distributed near the CPU socket and the motherboard external power interface. The common capacitors on the motherboard are aluminum electrolytic capacitor, tantalum capacitor, ceramic chip capacitor, etc.
Aluminum electrolytic capacitor vertical capacitor is our most common capacitor, which is usually more near CPU and memory slot. Aluminum electrolytic capacitor has large volume and large capacity; tantalum capacitor ceramic chip capacitor is generally small, with black chip appearance.
It has small volume, good heat resistance, low loss, but small capacity, which is generally suitable for high-frequency circuit, and is widely used on motherboard and video card.
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