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Hardware basics


Table 4.1: Typical system parameters in 2007. The seek time is the time needed to position the disk head in a new position. The transfer time per byte is the rate of transfer from disk to memory when the head is in the right position.
 Symbol Statistic Value  
 $s$ average seek time 5 ms $=$ $5\times 10^{-3}$ s  
 $b$ transfer time per byte 0.02 $\mu$s $=$ $2 \times 10^{-8}$ s  
   processor's clock rate $10^{9} \ \mbox{s}^{-1}$  
 $p$ lowlevel operation    
       (e.g., compare & swap a word) 0.01 $\mu$s $=$ $10^{-8}$ s  
   size of main memory several GB  
   size of disk space 1 TB or more  

When building an information retrieval (IR) system, many decisions are based on the characteristics of the computer hardware on which the system runs. We therefore begin this chapter with a brief review of computer hardware. Performance characteristics typical of systems in 2007 are shown in Table 4.1 . A list of hardware basics that we need in this book to motivate IR system design follows.


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2009-04-07