Direct Memory Access
Under the Amiga architecture, the Agnus (Alice on AGA models) coprocessor is the direct memory access (DMA) controller. Both the CPU and other members of the chipset have to arbitrate for access to shared RAM via Agnus. This allows the custom chips to perform video, audio or other DMA operations independently of the CPU. As the 68000 processor used in early Amiga systems usually accesses memory on every second memory cycle, Agnus operates a system where the "odd" clock cycle is allocated to time-critical custom chip access and the "even" cycle is allocated to the CPU, thus the CPU is not typically blocked from memory access and may run without interruption. However, certain chipset DMA, such as copper or blitter operations, can use any spare cycles, effectively blocking cycles from the CPU. In such situations CPU cycles are only blocked while accessing shared RAM, but never when accessing external RAM or ROM.
Read more about this topic: Amiga Chip RAM
Famous quotes containing the words direct, memory and/or access:
“James’s great gift, of course, was his ability to tell a plot in shimmering detail with such delicacy of treatment and such fine aloofness—that is, reluctance to engage in any direct grappling with what, in the play or story, had actually “taken place”Mthat his listeners often did not, in the end, know what had, to put it in another way, “gone on.””
—James Thurber (1894–1961)
“Memory is like a purse,—if it be over-full that it cannot shut, all will drop out of it. Take heed of a gluttonous curiosity to feed on many things, lest the greediness of the appetite of thy memory spoil the digestion thereof.”
—Thomas Fuller (1608–1661)
“The professional celebrity, male and female, is the crowning result of the star system of a society that makes a fetish of competition. In America, this system is carried to the point where a man who can knock a small white ball into a series of holes in the ground with more efficiency than anyone else thereby gains social access to the President of the United States.”
—C. Wright Mills (1916–1962)