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#4617 - 10/02/09 08:25 AM 32 bit vs 64 bit
joemikeb Offline
Moderator

Registered: 08/04/09
Loc: Fort Worth, Texas
I finally got around to running a benchmark comparison between running 64 bit mode and 32 bit mode on my 24" iMac 3.06 GHz core 2 duo with 4 GB of matched RAM. The results follow with 32 bit mode first and 64 bit second. The "winner" in each category is highlighted in red. Note this is the result of very limited trials and I do not pretend it to be scientifically valid. It is merely a data point.

System Info
Xbench Version 1.3
System Version 10.6.1 (10B504)
Physical RAM 4096 MB
Model iMac8,1
Drive Type WDC WD5000AAKS-40YGA1

32 Bit Tests
Results 157.13
CPU Test 218.71
Thread Test 369.12
Memory Test 222.32
Quartz Graphics Test 239.47
OpenGL Graphics Test 101.17
User Interface Test 307.02
Disk Test 64.71

64 Bit Tests
Results 165.75
CPU Test 184.85
Thread Test 406.08
Memory Test 224.22
Quartz Graphics Test 244.88
OpenGL Graphics Test 102.42
User Interface Test 329.76
Disk Test 76.81

Surprises:
  • The 32 bit CPU score being 18% higher (faster) than the 64 bit score
  • The 64 bit Disk Test being 18% higher (faster) than the 32 bit score
  • Although the 64 bit overall score is only 5% better than the 32 bit score, 64 bit mode "feels" a lot snappier. I can only attribute that to the impact of the greatly improved disk performance in the 64 bit mode.
The next thing to try is iBench to see if the 64 bit/32bit differential shows up there.
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#4690 - 10/04/09 11:04 PM Re: 32 bit vs 64 bit [Re: joemikeb]
sandbox Offline


Registered: 08/04/09
Loc: Water World
If I'm understanding this point, the CPU is no longer taxed as much in the 64 bit mode, and so it runs at a slower pace? It does more work with less effort?

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#4754 - 10/06/09 04:43 PM Re: 32 bit vs 64 bit [Re: sandbox]
tacit Offline


Registered: 08/03/09
Loc: Portland, Oregon, USA
Not really, no.

On its most basic surface, a 64-bit system addresses more memory (the RAM limit in a 32-bit system is 4 GB) and can process data 64 bits rather than 32 bits at a time; in that sense, a 64-bit processor actually works harder, because it's processing more data at once.

In practice, OS X up until 10.6 is a hybrid, combining 64-bit and 32-bit systems. The way memory is addressed has implications for the virtual memory system, which in turn affects how VM files are read and written to disk, and affects just about every other part of the system, so naturally you'll see differnces throughout the system. In general, 64-bit systems should be faster, especially on computers with more than 4 GB of RAM installed.
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#4758 - 10/07/09 01:13 AM Re: 32 bit vs 64 bit [Re: tacit]
sandbox Offline


Registered: 08/04/09
Loc: Water World
Thanks for the explanation, I haven't quite got my head around it and when I saw the slower CPU rate it was confusing.

So, if he adds more than 4GB of RAM then the 64 bit advantage will be noticed, but at 4GB the 32bit test is optimal as far as CPU speed, or is there something else slowing down his CPU test?

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#4773 - 10/07/09 07:54 AM Re: 32 bit vs 64 bit [Re: sandbox]
joemikeb Offline
Moderator

Registered: 08/04/09
Loc: Fort Worth, Texas
My guess is the slower CPU speed is a result of having to load two 32 bit data "words" for each 64 bit operation. In other words although it crunches the data twice as fast, it takes longer to load it into the memory registers. However without spending a few hours with schematics, etc. of the core 2 duo processor I cannot verify that.
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#4775 - 10/07/09 10:15 AM Re: 32 bit vs 64 bit [Re: joemikeb]
joemikeb Offline
Moderator

Registered: 08/04/09
Loc: Fort Worth, Texas
I said I was going to do this and I just got around to running iBench. XBench, which I already reported, tests the overall system performance while iBench zeros in on specific aspects of the CPU itself. And the results are:

32 Bit Mode Composite Score: 4.31
64 bit Mode Composite Score: 4.28

So the Core 2 Duo processor is in fact very slightly slower running in 64 bit mode than it is in 32 bit mode. On the other hand, as I mentioned earlier the overall system performance is better in 64 bit mode and I find the overall "feel" to be a noticeably "snappier" in 64 bit mode, so that is my default mode.
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