Norton System Index: A CPU and (optional) disk performance measurement built into the Norton Utility package -- distributed by Symantec. CPU SI apparently works by measuring time required to repeatedly execute a small program loop heavily weighted toward integer multiply and divide (one CPU manufacturer claims the main loop is only 6 instructions). SI is easily and widely used as a CPU/motherboard measurement. Although widely used, SI suffers from a number of deficiencies. Values vary from version to version. On cached machines, SI will run almost entirely from the highest level cache. The SI CPU values are not linear. A 10% increase in SI does not necessarily indicate a 10% improvement in performance. Machines that appear to be similar in performance may yield substantially different SI scores and vice versa. Example: One set of measurements showed a 1300% improvement in SI from activating a 486 L1 cache and a 50% difference between write thru and write back caching. More realistic numbers are 100% and 2-20% respectively.

Older versions of Norton SI overflow in timing computations on computers in the P200 and faster range.

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