NS4Sale - Nova Scotia Classifieds Buy, Sell & Swap - View Single Post

Rednecktech · 03-11-2008, 10:48 PM

It's true. Pentium D's suck, it's all about clock cycles among other things.

Quote:

Instructions per Cycle: Get in Gear

To add up a column of numbers with a pocket calculator, you simply type each number in and press the "+" key (or the "=" key at the end). Most users probably think that a PC spreadsheet program does the same thing. However, the human brain has actually been doing the hard part of the operation, moving down one row in the column, focusing on the number, and recognizing it. Each PC instruction carries with it a number of additional operations that would not be obvious to the casual user.

First, the computer must locate the next instruction in memory and move it to the CPU. This instruction is coded as a number. The computer must decode the number to determine the operation (say ADD), and the size of the data (say 16-bits). Additional information is then moved and decoded to determine the location in memory (the row and column of the spreadsheet). Finally, the number is added to the running total. Although a human might take some time to add two eight digit numbers together, the addition is the simplest part of the operation for a computer chip. Decoding the instruction and locating the data take the most time.

Each generation of Intel CPU chip has performed this operation in fewer clock cycles than the previous generation.

* A 386 CPU required a minimum of 6 clock ticks to add two numbers.
* A 486 CPU could generally add two numbers in two clock ticks.
* A Pentium CPU could add two numbers in a single clock tick.
* A modern processor can add two to six pairs of numbers in a single clock tick. If it discovers that the next instruction needs data that hasn't arrived from slow memory, it can rearrange things to execute subsequent instructions until the data arrives.

To make a car go faster, one steps on the accelerator. Extra gas makes the engine rotate faster. When RPM gets high enough, it is better to shift to a higher gear. The PC system clock (measured in MHz) is like the engine speed (measured in RPM). The CPU model selects the gear. The original 86 processor was like first gear, and the 486 is like fourth gear. So it is a mistake to compare clock speed across changes in the architecture.

This explains the current difference between Intel and AMD chip speeds. AMD has more internal processing units, so it executes more instructions at the same clock speed. AMD therefore quotes its processor by the equivalent Intel processor speed and not the actual clock.