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An important message from System 7 Today founder Dan Palka
 Topic: Speed Doubler (Page 1 of 1)
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Posted: Thu Jul 12, 2012 12:52 pm
I saw the section on Speed Doubler and wanted to comment. The gist is that if my memory is accurate, Speed Doubler will grant a significant improvement in performance of 68K code on NuBus PowerMacs, but not on PCI PowerMacs.

The 68K emulators built into the Apple ROMs convert the 68K code into PPC instructions as the machine marches through the code. Of course, the conversion process requires CPU cycles as well, which is what makes emulation slow.

In the original (NuBus) PowerMacs, the emulator converts an instruction, executes it, and discards it. It's like a Basic Interpreter.

Speed Doubler is more efficient because it converts sections of code and retains a cache of the converted code for reuse. So looping structures, for example, execute much more quickly.

However, if I remember correctly, in the PCI PowerMacs Apple either licensed Speed Doubler's technology or they implemented their own dynamic compiling technology, so there really isn't much advantage in using Speed Doubler on a PCI PowerMac. Although some of the disk and file copy utilities are kind of nice.
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