Editing Operating system (section)

=====Hardware interrupt=====
[[Input/output]] (I/O) [[Peripheral|devices]] are slower than the CPU. Therefore, it would slow down the computer if the CPU had to [[Busy waiting|wait]] for each I/O to finish. Instead, a computer may implement interrupts for I/O completion, avoiding the need for [[Polling (computer science)|polling]] or busy waiting.<ref name="sco-ch5-p292">{{cite book
  | last = Tanenbaum
  | first = Andrew S.
  | title = Structured Computer Organization, Third Edition
  | publisher = Prentice Hall
  | year = 1990
  | page = [https://archive.org/details/structuredcomput00tane/page/292 292]
  | isbn = 978-0-13-854662-5
  | url = https://archive.org/details/structuredcomput00tane/page/292
  }}</ref>

Some computers require an interrupt for each character or word, costing a significant amount of CPU time. [[Direct memory access]] (DMA) is an architecture feature to allow devices to bypass the CPU and access [[random-access memory|main memory]] directly.<ref name=A22-6821-7-storage>{{cite book
 |author       = IBM
 |title        = IBM System/360 Principles of Operation
 |date         = September 1968
 |version      = Eighth Edition
 |url          = http://bitsavers.org/pdf/ibm/360/princOps/A22-6821-7_360PrincOpsDec67.pdf
 |section      = Main Storage
 |section-url  = http://bitsavers.org/pdf/ibm/360/princOps/A22-6821-7_360PrincOpsDec67.pdf#page=8
 |mode         = cs2
 |page         = 7
 |access-date  = 13 April 2022
 |archive-date = 19 March 2022
 |archive-url  = https://web.archive.org/web/20220319083255/http://bitsavers.org/pdf/ibm/360/princOps/A22-6821-7_360PrincOpsDec67.pdf
 |url-status   = live
}}</ref> (Separate from the architecture, a device may perform direct memory access{{efn|often in the form of a DMA chip for smaller systems and I/O channels for larger systems}} to and from main memory either directly or via a bus.)<ref name="sco-ch5-p294">
{{cite book
  | last = Tanenbaum
  | first = Andrew S.
  | title = Structured Computer Organization, Third Edition
  | publisher = Prentice Hall
  | year = 1990
  | page = [https://archive.org/details/structuredcomput00tane/page/294 294]
  | isbn = 978-0-13-854662-5
  | url = https://archive.org/details/structuredcomput00tane/page/294
  }}</ref>{{efn|Modern [[motherboard]]s have a DMA controller. Additionally, a device may also have one. Visit [[SCSI RDMA Protocol]].}}