Limitations of Practical Processors
In principle, a 64-bit microprocessor can address 16 exabytes of memory. In practice, it is less than that.
For example, the AMD64 architecture as of 2011 allows 52 bits for physical memory and 48 bits for virtual memory. These limits allow memory sizes of 4 PiB (4 × 10245 bytes) and 256 TiB (256 × 10244 bytes), respectively. A PC cannot contain 4 petabytes of memory (due to the physical size of the memory chips, if nothing else) but AMD envisioned large servers, shared memory clusters, and other uses of physical address space that might approach this in the foreseeable future, and the 52-bit physical address provides ample room for expansion while not incurring the cost of implementing 64-bit physical addresses. Similarly, the 48-bit virtual address space was designed to provide more than 65,000 times the 32-bit limit of 4 GiB (4 × 10243 bytes), allowing room for later expansion without incurring the overhead of translating full 64-bit addresses.
Read more about this topic: 64-bit Computing
Famous quotes containing the words limitations of, limitations, practical and/or processors:
“The motion picture made in Hollywood, if it is to create art at all, must do so within such strangling limitations of subject and treatment that it is a blind wonder it ever achieves any distinction beyond the purely mechanical slickness of a glass and chromium bathroom.”
—Raymond Chandler (1888–1959)
“The motion picture made in Hollywood, if it is to create art at all, must do so within such strangling limitations of subject and treatment that it is a blind wonder it ever achieves any distinction beyond the purely mechanical slickness of a glass and chromium bathroom.”
—Raymond Chandler (1888–1959)
“The English masses are lovable: they are kind, decent, tolerant, practical and not stupid. The tragedy is that there are too many of them, and that they are aimless, having outgrown the servile functions for which they were encouraged to multiply. One day these huge crowds will have to seize power because there will be nothing else for them to do, and yet they neither demand power nor are ready to make use of it; they will learn only to be bored in a new way.”
—Cyril Connolly (1903–1974)
“The information links are like nerves that pervade and help to animate the human organism. The sensors and monitors are analogous to the human senses that put us in touch with the world. Data bases correspond to memory; the information processors perform the function of human reasoning and comprehension. Once the postmodern infrastructure is reasonably integrated, it will greatly exceed human intelligence in reach, acuity, capacity, and precision.”
—Albert Borgman, U.S. educator, author. Crossing the Postmodern Divide, ch. 4, University of Chicago Press (1992)