Editing Microprocessor (section)

==Structure==
[[File:Z80 arch.svg|thumb|upright=1.7|A block diagram of the architecture of the [[Zilog Z80|Z80]] microprocessor, showing the [[Arithmetic logic unit|arithmetic and logic section]], [[Processor register|register]] file, [[control logic]] section, and [[Data buffer|buffer]]s to external [[Memory address|address]] and data lines]]

The complexity of an integrated circuit is bounded by physical limitations on the number of [[transistors]] that can be put onto one chip, the number of package terminations that can connect the processor to other parts of the system, the number of interconnections it is possible to make on the chip, and the heat that the chip can [[Thermal management (electronics)|dissipate]]. Advancing technology makes more complex and powerful chips feasible to manufacture.

A minimal hypothetical microprocessor might include only an [[arithmetic logic unit]] (ALU), and a [[control logic]] section. The ALU performs addition, subtraction, and operations such as AND or OR. Each operation of the ALU sets one or more [[Bit field|flag]]s in a [[status register]], which indicate the results of the last operation (zero value, negative number, [[Integer overflow|overflow]], or others). The control logic retrieves instruction codes from memory and initiates the sequence of operations required for the ALU to carry out the instruction. A single [[operation code]] might affect many individual data paths, registers, and other elements of the processor.

As integrated circuit technology advanced, it was feasible to manufacture more and more complex processors on a single chip. The size of data objects became larger; allowing more transistors on a chip allowed [[Word (computer architecture)|word]] sizes to increase from [[4-bit computing|4-]] and [[8-bit]] words up to today's [[64-bit]] words. Additional features were added to the processor architecture; more on-chip registers sped up programs, and complex instructions could be used to make more compact programs. [[Floating-point arithmetic]], for example, was often not available on 8-bit microprocessors, but had to be carried out in [[software]]. Integration of the [[floating-point unit]], first as a separate integrated circuit and then as part of the same microprocessor chip, sped up floating-point calculations.

Occasionally, physical limitations of integrated circuits made such practices as a [[bit slice]] approach necessary. Instead of processing all of a long word on one integrated circuit, multiple circuits [[parallel computing|in parallel]] processed subsets of each word. While this required extra logic to handle, for example, carry and overflow within each slice, the result was a system that could handle, for example, [[32-bit]] words using integrated circuits with a capacity for only four&nbsp;bits each.

The ability to put large numbers of transistors on one chip makes it feasible to integrate memory on the same die as the processor. This [[CPU cache]] has the advantage of faster access than off-chip memory and increases the processing speed of the system for many applications. Processor [[clock frequency]] has increased more rapidly than external memory speed, so [[cache memory]] is necessary if the processor is not to be delayed by slower external memory.

The design of some processors has become complicated enough to be difficult to fully [[Integrated circuit testing|test]], and this has caused problems at large cloud providers.<ref>{{Cite web |url=https://www.theregister.com/2021/06/04/google_chip_flaws/ |title=FYI: Today's computer chips are so advanced, they are more 'mercurial' than precise – and here's the proof |access-date=13 February 2024 |archive-date=13 February 2024 |archive-url=https://web.archive.org/web/20240213173804/https://www.theregister.com/2021/06/04/google_chip_flaws/ |url-status=live }}</ref>

===Special-purpose designs===
A microprocessor is a general purpose processing entity. Several specialized processing devices have followed:

* A [[digital signal processor]] (DSP) is specialized for [[signal processing]].
* [[Graphics processing unit]]s (GPUs) are processors designed primarily for [[real-time rendering]] of images.
* Other specialized units exist for [[video processing]] and [[vision processing unit|machine vision]]. (See: [[Hardware acceleration]].)
* [[Microcontroller]]s in [[embedded system]]s and [[peripheral device]]s. 
* [[Systems on chip]] (SoCs) often integrate one or more microprocessor and microcontroller cores with other components such as [[radio modem]]s, and are used in smartphones and tablet computers.

===Speed and power considerations===
[[File:Intel i9-9900K.jpg|thumb|Intel Core i9-9900K (2018, based on [[Coffee Lake]])]]
Microprocessors can be selected for differing applications based on their word size, which is a measure of their complexity. Longer word sizes allow each [[clock cycle]] of a processor to carry out more computation, but correspond to physically larger integrated circuit dies with higher standby and operating [[power consumption]].<ref name="cmicrotek">CMicrotek.
[http://cmicrotek.com/wordpress_159256135/?p=22 "8-bit vs 32-bit Micros"] {{webarchive|url=https://web.archive.org/web/20140714123158/http://cmicrotek.com/wordpress_159256135/?p=22 |date=2014-07-14 }}.</ref> 4-, 8- or 12-bit processors are widely integrated into microcontrollers operating embedded systems. Where a system is expected to handle larger volumes of data or require a more flexible [[user interface]], 16-, 32- or 64-bit processors are used. An 8- or [[16-bit]] processor may be selected over a 32-bit processor for [[system on a chip]] or microcontroller applications that require extremely [[low-power electronics]], or are part of a [[mixed-signal integrated circuit]] with noise-sensitive on-chip [[analog electronics]] such as high-resolution analog to digital converters, or both.
Some people say that running 32-bit arithmetic on an 8-bit chip could end up using more power, as the chip must execute software with multiple instructions.<ref>{{cite web|title=Managing the Impact of Increasing Microprocessor Power Consumption|url=http://www.ruf.rice.edu/~mobile/elec518/readings/Intel/gunther01power.pdf|website=[[Rice University]]|access-date=October 1, 2015|url-status=live|archive-url=https://web.archive.org/web/20151003085353/http://www.ruf.rice.edu/~mobile/elec518/readings/Intel/gunther01power.pdf|archive-date=October 3, 2015}}</ref>
However, others say that modern 8-bit chips are always more power-efficient than 32-bit chips when running equivalent software routines.<ref name="freeman" >Wayne Freeman.
[https://www.electronicdesign.com/technologies/microcontrollers/article/21802087/11-myths-about-8bit-microcontrollers "11 Myths About 8-Bit Microcontrollers"] {{Webarchive|url=https://web.archive.org/web/20220812175959/https://www.electronicdesign.com/technologies/microcontrollers/article/21802087/11-myths-about-8bit-microcontrollers |date=12 August 2022 }}.
2016.
quote:
"Basically, by getting your work done faster, you can put the CPU in sleep mode for longer periods of time. Thus, 32-bit MCUs are more power-efficient than 8-bit MCUs, right? Wrong."</ref>