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Author Topic: What is PrefetchW ?  (Read 28202 times)

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Geek-9pm

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What is PrefetchW ?
« on: August 15, 2014, 02:08:53 PM »
I went to install Windows 8.1 trial and it asked me if I wanted to check for dow2nloads. I said yes, it took awhile, then it said:
Quote
You can't install Windows 8.1 because your processor doesn't support PrefetchW.
What? Never here of it.  ???

BC_Programmer


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Re: What is PrefetchW ?
« Reply #1 on: August 15, 2014, 03:40:09 PM »
It is a CPU instruction.
I was trying to dereference Null Pointers before it was cool.

Salmon Trout



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Re: What is PrefetchW ?
« Reply #2 on: August 15, 2014, 04:25:02 PM »

Salmon Trout



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Re: What is PrefetchW ?
« Reply #3 on: August 16, 2014, 01:25:22 AM »
For 64 bit installations of Windows 8.1 the CPU must support CMPXCHG16b, PrefetchW and LAHF/SAHF instructions. PrefetchW is an AMD 3DNow! instruction and Intel desktop processors became compatible from family 15/model 6/stepping 1 (Cedar Mill, the 65 nM final revision of the Pentium 4 released on January 5, 2006) thus I should think all 90 nM Pentium 4 era CPUs and earlier are incompatible (Prescott and earlier).

Salmon Trout



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Re: What is PrefetchW ?
« Reply #4 on: August 16, 2014, 03:53:54 AM »
Geek, on your profile your listed machines use the following CPUs:

Dell E1705 cpu: Intel Core Duo T2500
Dell GX520 cpu: Intel Pentium 4

Which machine are you talking about? If it is the Optiplex GX520 desktop, that uses a Prescott era Pentium 4 and would not be Windows 8.1 compatible.




Geek-9pm

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Re: What is PrefetchW ?
« Reply #5 on: August 16, 2014, 04:49:20 PM »
Dell GX520 CPU Intel Pentium 4
I was trying a 64 bit Windows 8.1

Strange, I had to replace that CPU because the chip set   did not fully support the new CPU in that group. After that I tried to install Windows 8.1 and is stalled opr gave the error message.

The machine runs Windows 7 64 bit with not problem.

Anyway, I am not going to rip it open and swap  the CPU again. Instead, I have Windows 8.1 now on a Dell 755 machine and it works.




patio

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Re: What is PrefetchW ?
« Reply #6 on: August 16, 2014, 05:12:44 PM »
Your an adventerous guy Geek...
" Anyone who goes to a psychiatrist should have his head examined. "

Geek-9pm

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Re: What is PrefetchW ?
« Reply #7 on: August 16, 2014, 05:19:38 PM »
Your an adventerous guy Geek...
For some reason Windows 7 64 does not seem to care about a missing code. But it seems to matter to Windows 8.1 and I can not run it on that machine.

Thanks to Salmon Trout for the research.  So did Intel have t o buy a bunch of PrefetchW jelly bean bits from AMD?
This may one of  the things science will never understand:P

Geek-9pm

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Re: What is PrefetchW ?
« Reply #8 on: August 16, 2014, 11:15:40 PM »
OK, some looking around shows this issue is well known. Some Intell Pentium CPU chips just don't have it. Hard to accept!  :'(
Look at this:
OK for Windows 8, but not 8.1
Quote
The CPU must also support the following
LAHF-SAHF * Supports LAHF/SAHF instructions in 64-bit mode
CX16 * Supports CMPXCHG16B instruction
PREFETCHW * Supports PREFETCHW instruction
The Intel Pentium D 820 does NOT support the last one :-( so it seems that I'm stuck on 8.0
Not likely MS will continue to support Windows 8.0 just for a few.
This may mean that a few people with the wrong CPU have to get both a new motherboard and a CPU if the chip set does not support the newer CPU. Thanks a lot, Intel!

Salmon Trout



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Re: What is PrefetchW ?
« Reply #9 on: August 17, 2014, 12:02:54 AM »
This may mean that a few people with the wrong CPU have to get both a new motherboard and a CPU if the chip set does not support the newer CPU. Thanks a lot, Intel!

I think you just have to suck it up; why should Microsoft hold back OS development to cater for people with hardware that is fit for the dumpster?

BC_Programmer


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Re: What is PrefetchW ?
« Reply #10 on: August 17, 2014, 02:23:38 AM »
I think you just have to suck it up; why should Microsoft hold back OS development to cater for people with hardware that is fit for the dumpster?

Bah Humbug! Why, this new "386 enhanced mode" is just a ploy by Intel I tell you!
I was trying to dereference Null Pointers before it was cool.

Salmon Trout



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Re: What is PrefetchW ?
« Reply #11 on: August 17, 2014, 02:27:58 AM »
I see I miswrote the unit for nanometres: the SI symbol is nm - small n small m


Salmon Trout



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Re: What is PrefetchW ?
« Reply #12 on: August 17, 2014, 04:16:24 AM »
OK, some looking around shows this issue is well known.

Why didn't you do that before starting this thread?

Geek-9pm

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Re: What is PrefetchW ?
« Reply #13 on: August 17, 2014, 02:03:50 PM »
Why didn't you do that before starting this thread?
Because I had never heard of it and did not know it was a problem. I just could not believe there was anything missing on my Pentium D dual core 64 bit Intel CPU.  It is not like  I was running an old Pentium that was missing part of the math math tables years ago. I thought that by now  Intel would have it all over with.

As was said in the thread, it is an instruction introduced by AMD.  It is part of the 3D set.
http://en.wikipedia.org/wiki/3DNow!
Quote
3DNow performance-enhancement instructions
    FEMMS Faster entry/exit of the MMX or floating-point state
    PREFETCH/PREFETCHW Prefetch at least a 32-byte line into L1 data cache (this is the non-deprecated instruction

I am glad I asked. The info from  Salmon Trout and others helped me understand. I am a slow learner an d I value the help of forum members. Besides, It is fun to come here.  ;D

Salmon Trout



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Re: What is PrefetchW ?
« Reply #14 on: August 17, 2014, 02:39:32 PM »
It is fun to come here.  ;D

A fair comment!