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I found that enabling Intel HD Graphics in device manager can increase memory speed about 17%. I also used Prime95 to test memory speed, and same result is found. (Prime95 results are highly dependent on memory speed)

My hardware information is below.

Processor: Intel Core i7-4790k (with Intel HD Graphics 4600)
Motherboard: Gigabyte B85M-D3H
Memory: Kingston 8GB 1600MHz x 2 (dual channel)

When HD Graphics is disabled, memory speed is about 18.3GB/s, and a iteration of Prime95 3584K FFT consume about 19ms. When HD Graphics is enabled, the result is about 21.4GB/s and 16ms.

Screenshot: when HD Graphics is DISABLED. disabled

Screenshot: when HD Graphics is ENABLED. enabled

I also tested some other configuration with Prime95, results are in the table below. With these tests, I found that the memory speed is fast, if and only if the HD Graphics is enabled with Windows operating system. The memory speed is slow even if a discrate graphics card is installed. 

#1
+------------------------------------------+--------+
| No discrate graphics card installed      | 20ms   |
| HD Graphics enabled in BIOS              | (slow) |
| Fresh install of Windows Server 2012 R2  |        |
| HD Graphics driver **not installed**     |        |
+------------------------------------------+--------+
| No discrate graphics card installed      | 15ms   |
| HD Graphics enabled in BIOS              | (fast) |
| Fresh install of Windows Server 2012 R2  |        |
| HD Graphics driver **installed**         |        |
+------------------------------------------+--------+

#2
+------------------------------------------+--------+
| No discrate graphics card installed      | 20ms   |
| HD Graphics disabled in BIOS             | (slow) |
| Use Remote Desktop to benchmark          |        |
| Fresh install of Windows Server 2012 R2  |        |
+------------------------------------------+--------+

#3
+------------------------------------------+--------+
| No discrate graphics card installed      | 20ms   |
| HD Graphics enabled in BIOS              | (slow) |
| Fresh install of Ubuntu 14.04.3          |        |
+------------------------------------------+--------+

#4
+------------------------------------------+--------+
| Geforce 6200LE graphics card installed   | 20ms   |
| HD Graphics disabled in BIOS             | (slow) |
| Fresh install of Windows Server 2012 R2  |        |
+------------------------------------------+--------+

My question is: why enabling Intel HD Graphics can increase memory speed?

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1
  • BIOS may increase RAM speed to help feed GPU. Anandtech has shown that faster RAM notably helps Intel on-board graphics speed.
    – StackAbstraction
    Commented Sep 11, 2015 at 5:56

1 Answer 1

Reset to default
-2

When using onboard graphics on AMD's APUs or in your case a Intel chip, part of the system memory is going to be used for graphics, GPU memory is alot faster than system RAM, so your motherboard is probably pushing the RAM a little more harder than usual. Are the allocated memory settings on the BIOS in auto? Setting them all to manual should remove the variable and the results should then be the same.

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2
  • 2
    Certainly, specialized graphics memory will usually be faster. Mainly because the interface is much much wider. But neither is this GDDR nor does it magically increase the interface width.
    – Daniel B
    Commented Sep 11, 2015 at 21:32
  • Of course its not magic, what I suggested is that it's some automatic optimization made by the motherboard, you should be able to use a dedicated gpu and still reach the same speeds tweeking the RAM settings
    – rzfzr
    Commented Sep 12, 2015 at 2:05

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