2 External Memory Model
نویسندگان
چکیده
It is clear that the fastest memory levels are substantially smaller than the slowest ones. Generally, each level has a direct connection to the level immediately below it. (In addition, the faster, smaller levels are substantially more expensive to produce, so do not expect 1GB of register space any time soon.) Additionally, many of the levels communicate in blocks. For example, asking RAM to read one integer will typically also transmit a “block” of nearby data. So processing the block members costs no additional memory transfers. This issue is exacerbated when communicating with the disk: the 10ms is dominated by the time needed to find the data (move the read head over the disk). Modern disks are circular, spinning at 7200rpm, so once the head is in position, reading all of the data on that “ring” is practically free.
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