For example the sumarraycols function in figure 619a

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Unformatted text preview: ms) is Ì Ú ÖÓØ Ø ÓÒ 1/2 ¢ ÌÑ 4 ms 1/2 ¢ ´60 secs / 7,200 RPMµ ¢ 1000 ms/sec Ü ÖÓØ Ø ÓÒ The average transfer time is Ì Ú ØÖ Ò× Ö 60 / 7,200 RPM ¢ 1 / 400 sectors/track ¢ 1000 ms/sec 0.02 ms Putting it all together, the total estimated access time is Ì ×× Ì Ú × · Ì Ú ÖÓØ Ø ÓÒ · Ì Ú ØÖ Ò× Ö 9 ms · 4 ms · 0.02 ms 13.02 ms This example illustrates some important points: 6.1. STORAGE TECHNOLOGIES 289 ¯ ¯ ¯ The time to access the 512 bytes in a disk sector is dominated by the seek time and the rotational latency. Accessing the first byte in the sector takes a long time, but the remaining bytes are essentially free. Since the seek time and rotational latency are roughly the same, twice the seek time is a simple and reasonable rule for estimating disk access time. The access time for a doubleword stored in SRAM is roughly 4 ns, and 60 ns for DRAM. Thus, the time to read a 512-byte sector-sized block from memory is roughly 256 ns for SRAM and 4000 ns for DRAM. The disk access time, roughly 10 ms, is about 40,000 times greater than SRAM, and about 2,500 times greater than DRAM. The difference...
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This note was uploaded on 09/02/2010 for the course ELECTRICAL 360 taught by Professor Schultz during the Spring '10 term at BYU.

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