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:
“Traditionally in American society, men have been trained for both competition and teamwork through sports, while women have been reared to merge their welfare with that of the family, with fewer opportunities for either independence or other team identifications, and fewer challenges to direct competition. In effect, women have been circumscribed within that unit where the benefit of one is most easily believed to be the benefit of all.”
—Mary Catherine Bateson (b. 1939)
“Those who believe in their truth—the only ones whose imprint is retained by the memory of men—leave the earth behind them strewn with corpses. Religions number in their ledgers more murders than the bloodiest tyrannies account for, and those whom humanity has called divine far surpass the most conscientious murderers in their thirst for slaughter.”
—E.M. Cioran (b. 1911)
“The nature of women’s oppression is unique: women are oppressed as women, regardless of class or race; some women have access to significant wealth, but that wealth does not signify power; women are to be found everywhere, but own or control no appreciable territory; women live with those who oppress them, sleep with them, have their children—we are tangled, hopelessly it seems, in the gut of the machinery and way of life which is ruinous to us.”
—Andrea Dworkin (b. 1946)