CPU TDP與其耗電關係

真衰鬼

打開Intel 或 AMD 官網，在每粒CPU的specification上，我絕大部份時間只見到一個名詞：TDP。
TDP以Watts表示，常見的有45W、65W、95W及125W。
這便令人聯想到TDP=耗電？
首先，甚麼是TDP？

Wiki
The thermal design power (TDP), sometimes calledthermal design point, represents the maximum amount of power the cooling systemin a computer is required to dissipate.

那這就是CPU的TDP了？
非也！
原來Intel及AMD各自有其CPU TDP的定義：

How does AMD define TDP?
“Thermal DesignPower (TDP) is measured under the conditions of TCASE Max, IDD Max, andVDD=VID_VDD, and include all power dissipated on-die from VDD, VDDIO, VLDT,VTT, and VDDA.”
This means thatTDP, as defined by AMD, is measured at the maximum current the CPU can draw, at the default voltage, under the worst-case temperature conditions.
This is the maximum power that the CPU can possibly dissipate.

我經師兄建議要補下英文後，便用雞腸打了電郵給AMD，所得的解釋為：

下載 (33.37 KB)

2010-6-10 21:50

那Intel 呢？

How does Intel define TDP?
From the Intel Datasheet for Northwood CPUs:
“The numbers inthis column reflect Intel’s recommended design point and are not indicative ofthe maximum power the processor can dissipate under worst case conditions.”
And from Intel’s datasheet for Prescott CPUs:
“Thermal DesignPower (TDP) should be used for processor thermal solution design targets. The TDP is not the maximum power that the processor can dissipate.”
And the most telling quote of all, contained in both documents:
“Analysis indicates that real applications are unlikely to cause the processor to consume maximum power dissipation for sustained periods of time. Intel recommends that complete thermal solution designs target the Thermal Design Power (TDP) indicated in Table 26 instead of the maximum processor power consumption. The Thermal Monitor feature is intended to help protect the processor in the unlikely event that an application exceeds the TDP recommendation for a sustained period of time.”
What this means is that Intel’s TDP is actually lower than the maximum power dissipation of the processor (and as you’ll see later, it can be significantly lower).
This is in stark contrast to AMD’s TDP numbers, which are higher than the respective processor’s maximum power dissipation.

以上的資料來自：
Submitted by Mike Chin on Tue, 2004-06-15 09:28

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說了這麼久，那CPU TDP能否用於估計其耗電呢？
我們不要考慮甚麼測試一D重型散熱好多時會燒機上呢D特殊情況，更多情況也有，但那如何討論？

以上的文章計算出有關某系列Intel CPU的耗電，發現最高耗電為TDP的1.1-1.15倍。
15%相差看似很大。
但以一粒TDP 125W 的CPU為例，其15%為19W，這19W差距對用於估計CPU耗電的參考，我個人認為是可以接受的。

那AMD呢？
文章顯示其TDP顯著高於其最高耗電。高多少百份比卻沒有具體說明。
但既然官方已解釋了甚麼是TDP，我認為用TDP估計其耗電也是對的。

s021304

知唔知D電去左TDP外 其他電用左係邊??

真衰鬼

知唔知D電去左TDP外 其他電用左係邊??
s021304 發表於 2010-6-10 22:46

EM？

win150

唔係話唔時幾多年前AMD轉左用average去計?

真衰鬼

唔係話唔時幾多年前AMD轉左用average去計?
win150 發表於 2010-6-10 23:55

TDP只表示最高耗電，但表示不了「通常」用多少電，才出左個ACP。
但話明是Average，那就不能知道其最高耗電了。

willy930

唔係話唔時幾多年前AMD轉左用average去計?
win150 發表於 2010-6-10 23:55

AFAIK, AMD only use ACP for Server CPUs.

taiwanese

TDP 以我認知就係粒CPU產生既熱量
65W 就係 65W 既熱量
但係冇65W既電,又點樣產生65W熱呢?
我以前係咁諗
跟住自己睇下睇下 發現有樣野叫廢熱
但係以番 "但係冇65W既電,又點樣產生65W熱呢?"
TDP亦都可以代表CPU既耗電標準

albert_ma

efficiency 可能得幾個%
如果TDP係65W，full load 用電就可能會係70W

熱量/用電係同CPU 既frequency/電壓有關係...尤其係電壓

lexal

好複雜~~

7ming

TDP 以我認知就係粒CPU最高產生既熱量
基本上，用電 = 熱量
By conversation of energy，粒CPU用左幾多電，就會有幾多output。
for example 有粒TDP 65W既CPU full load時食左 60W 電，由於運算結果並唔係能量，所以CPU會output Exactly 60W EM Wave & Heat。但係基本上EM Wave因為都幾細下，所以可以當係60W Heat。