Why do a lot Pentium M line CPUs lack PAE?

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Why do a lot Pentium M line CPUs lack PAE?

Postposted on Sat Oct 06, 2012 1:50 pm

Virtually all Intel processors from 1995 - today support except except a bunch of Pentium M processors. Why would they cut it?
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Re: Why do a lot Pentium M line CPUs lack PAE?

Postposted on Sun Oct 07, 2012 2:30 pm

Intel has a long history of selectively enabling/disabling specific features to segment their product lineup. This allows them to charge customers who need those features a higher price, without having to design different chips. They have also used 64-bit instruction support and hardware virtualization this way; and their desktop chipsets/CPUs typically don't support ECC DRAM (even though it would be simple to do so - nearly all of AMD's CPUs going back to the original Athlon64 support ECC), to push people who want higher reliability to move to the more expensive Xeon platform.

For a particularly egregious example, see the 486SX and 487SX.

In the case of PAE, it is also possible that the feature simply wasn't ready for the initial Pentium M launch. As customers started to demand the NX bit feature (which requires PAE), they decided to incorporate it into the design.
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Re: Why do a lot Pentium M line CPUs lack PAE?

Postposted on Sun Oct 07, 2012 2:59 pm

A cynical man would say they didn't want things like this to become more widespread. The P6-derived Tualatin Pentium III and sub-derivative Pentium M were originally released as stop-gap mobile and SFF solutions after the Pentium 4 failed to scale down to mobile-appropriate power/performance levels.

By the time later Dothan variants were release with the NX-bit enabled, Intel had mostly given up on the "NetBurst" architecture and their roadmaps were already looking forward to the P6-derived "Core" products.
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Re: Why do a lot Pentium M line CPUs lack PAE?

Postposted on Sun Oct 07, 2012 2:59 pm

Only Banias and revisions of Dothan from before Q1 2005 lacked PAE/NX support.

Service Pack 2 for Windows XP introduced DEP (which leverages PAE) in August 25, 2004.

The Pentium M line were intended as laptop only chips. They were vastly superior to the Pentium 4 of the time, in my opinion, but they were not sold on the desktop and did not directly compete against the Pentium 4.

Laptops of that era did not need 36bit memory addressing. My 760 Dothan did support NX and PAE, but the accompanying 915PM chipset maxed out at 2GB of RAM and only had 32bit addressing.

In short the product was never in a market that needed PAE and the hardware ecosystem around the Pentium M didn't support PAE. When a software need arose (DEP) it gained the functionality back.
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Re: Why do a lot Pentium M line CPUs lack PAE?

Postposted on Sun Oct 07, 2012 3:06 pm

ludi wrote:A cynical man would say they didn't want things like this to become more widespread.


Cynical? No need to doubt that view point. Preventing systems like that were precisely why IMO.
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Re: Why do a lot Pentium M line CPUs lack PAE?

Postposted on Sun Oct 07, 2012 9:56 pm

Probably the same reason my new Cedar Trail laptop with hardware x64 support and DX 10.1 graphics is stuck using 32 bit Windows and DX9 graphics (no drivers, no BIOS support).

Also the same reason Celeron and Pentium CPUs, based on the Sandy Bridge architecture, can't use Smart Response.


Idiotic management, that's what.
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