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Intel Core i5 and Core i7 Lynnfield review

Is Hyper-Threading worth it?

Although Hyper-Threading has been available in various Intel CPUs since the Xeon MP in 2002, Intel deems it so important that it's Hyper-Threading support (and not trivialities such as socket type or memory support) that delineates between Core i5 and Core i7 processors.

We therefore wanted to investigate whether the status that Intel gives Hyper-Threading is really merited. In short, Hyper-Threading tricks the operating system into thinking there are twice as many processing cores in the system as are actually present. This is possible, since even when a processor core is at 100 per cent load, there will be some resources (such as the FPU units) that aren't used. The ability to send two execution threads through a single processor core is intended to accelerate multi-threaded applications and multi-tasking.

To put Hyper-Threading to the test, we benchmarked the Core i7-860 with it enabled and disabled in the BIOS. The tests were run with Turbo Boost (rev 2) disabled in the BIOS so that the CPU was running at the same constant frequency during the tests.

WPrime v2.00 HT

32M test, all process threads

  • Intel Core i7-860 (HT on)
  • Intel Core i7-860 (HT off)
    • 8.704
    • 9.421
0
3
5.5
8
10.5
seconds (lower is better)
  • Stock Speed

GIMP Image Editing Test HT

Custom PC Benchmark

  • Intel Core i7-860 (HT on)
  • Intel Core i7-860 (HT off)
    • 1029
    • 1080
0
250
500
750
1000
points (higher is better)
  • Stock Speed

Handbrake Video Encoding Test HT

Custom PC Benchmark

  • Intel Core i7-860 (HT on)
  • Intel Core i7-860 (HT off)
    • 2121
    • 1990
0
500
1000
1500
2000
points (higher is better)
  • Stock Speed

Multi-tasking Test (7-Zip and mplayer) HT

Custom PC Benchmark

  • Intel Core i7-860 (HT on)
  • Intel Core i7-860 (HT off)
    • 1278
    • 1356
0
250
500
750
1000
1250
1500
points (higher is better)
  • Stock Speed

Overall Custom PC Benchmark Score HT

Custom PC Benchmark

  • Intel Core i7-860 (HT on)
  • Intel Core i7-860 (HT off)
    • 1476
    • 1475
0
250
500
750
1000
1250
1500
points (higher is better)
  • Stock Speed

Crysis HT

Crysis v1.21, 64-bit, DX10, High, 1,680 x 1,050 2x AA no AF

  • Intel Core i7-860 (HT on)
  • Intel Core i7-860 (HT off)
    • 33
    • 25
    • 33
    • 26
0
5
10
15
20
25
30
35
fps (higher is better)
  • Average
  • Minimum

X3: Terran Conflict HT

Rolling Demo, v1.2.0.0, 1,680 x 1,050, 4x AA no AF

  • Intel Core i7-860 (HT on)
  • Intel Core i7-860 (HT off)
    • 76
    • 35
    • 78
    • 38
0
10
20
30
40
50
60
70
80
fps (higher is better)
  • Average
  • Minimum

Power Consumption, Idle HT

Power at wall socket. BIOS Defaults, all onboard hardware enabled. Windows desktop, Aero enabled, Id

  • Intel Core i7-860 (HT on)
  • Intel Core i7-860 (HT off)
    • 92
    • 90
0
25
50
75
100
Watts (lower is better)
  • Stock Speed

Power Consumption, Load HT

Power at wall socket. BIOS Defaults, all onboard hardware enabled. Prime95 Load

  • Intel Core i7-860 (HT on)
  • Intel Core i7-860 (HT off)
    • 179
    • 162
0
50
100
150
200
Watts (lower is better)
  • Stock Speed

As usual with Hyper-Threading, highly multi-threaded yet relatively simple tasks that such as video encoding and ray tracing reacted well. The video encoding test of our Media Benchmarks ran eight per cent faster with Hyper-Threading on, and Cinebench completed 13 per cent quicker.

However, the image editing and multi-tasking tests and games all ran slightly slower with Hyper-Threading enabled. Unfortunately, this is something we've come to expect. Despite several tweaks over the years, if either execution thread requires access to the same resource unit of the CPU's execution core at the same time, the second execution thread must queue until the unit is free. This 'thread stalling' explains why more complicated tasks might run slower with Hyper-Threading enabled.

With that said, we found that the slowdown due to Hyper-Threading was less than five per cent, and as Hyper-Threading doesn't increase the power consumption of your PC, enabling Hyper-Threading is worthwhile. Unless we really needed the extra multi-threaded performance, we wouldn't go out of our way to have Hyper-Threading, though, so we're mystified as to why Intel felt it necessary to differentiate its Core i5 and Core i7 ranges on this feature alone.