Am Mon, Mar 27, 2023 at 07:24:47AM -0400 schrieb Rich Freeman: > > Of course, only you can answer that in the end. Write down what you need and > > what you care about. Weigh those factors. Then decide. Raw CPU power, > > electricity bill, heat budget (cooling, noise, dust), the “new and shiny” > > factor (like DDR5), and price. As I mentioned earlier, the 7xxx-X series are > > hotheads. But when run with a lower power budget, they are very efficient > > (which is basically what the non-X do). > > Are they actually hotheads on an energy consumed per unit of work > basis? As you say, they're efficient. If the CPU has 2x the power > draw, but does 2.5x as much work in a unit of time than the "cooler" > CPU you're comparing it to, then actually doing any job is going to > consume less electricity and produce less heat - it is just doing it > faster. > […] > A recent trend is upping the power draw of CPUs/GPUs to increase their > throughput, but as long as efficiency remains the same, it creates > some thermal headaches, but doesn't actually make the systems use more > energy for a given amount of work. Of course if you throw more work > at them then they use more energy.
Back in the day, CPUs were sold to run at an optimum work point, meaning a compromise between silicon wafer yield, power consumption and performance. Some of the chips were so good, they had the potential for overclocking, meaning they are stable enough to be clocked higher and to handle the heat. (But at no guarantee from the manufacturer, I presume. So if you grill it, it’s your loss.) And heat there was: you could increase a CPU from 4 GHz to 4.4 GHz (10 % increase), but at a lot more power draw than just 10 %. The performance curve flattens at the high end; processing power does not scale linearly with power consumption beyond a certain point (else we would do it already). These days, modern high-end CPUs seem to come over-clocked from the factory. Instead, if the user wants to run at a more efficient mode, the BIOS offers ways to tune down the power budget. You lose 10..20 % in performance, but gain 20 K in cooling and 30 % or more in power consumption. 10 years ago, when the very efficient Core architecture swept the market, the high-end “extreme” Haswell models drew 140 W. [0] Comare that to current generations [1] (Intel) or [2] (AMD), those go beyond 200 W. Of course they are much much faster, but average-Joe doesn’t need that. Looking at concrete examples, the Ryzen 7900 has 3.7 GHz sustained max frequency (meaning no thermal throttling) at 65 W. The 7900X has 4.7 GHz (a quarter more) and 200 MHz more boost frequency, but is rated at 2½ times the wattage. The TDP does not tell you how much power the chip takes at most anymore (it can actually take much more in bursts or when it is still cool), but for how much thermal energy the cooling system needs to be designed in order to keep up the maximum (non-turbo, I think) frequency under load. This means that for a short time or on a low number of cores, the non-X can sustain almost as much boost clock as the X (it is the same silicon, after all), but once the cooling can’t keep up, it will throttle. I’m not very good at explaining the math or providing hard numbers from memory, because all I know about this matter is from reading the occasional review. So please have a read yourself (see below). Another reason to take my word with a grain of salt: I am biased towards environmentally friendly choices. Power may still be cheap where you live, but every kWh produced has an impact on the globe. Power efficiency (“points per Watt” metric): https://www.techpowerup.com/review/amd-ryzen-9-7900x/24.html Ryzen 7 5700G (i.e. laptop APU): 240.7 points Ryzen 7 5700X: 84.5 Ryzen 7 7700X: 83.0 Ryzen 9 7900X: 47.2 at stock (meaning no down-scaling) A comparison at https://www.xda-developers.com/amd-ryzen-9-7900-review/ shows only around 10 % more performance for the 7900X vs. the 7900: “The Ryzen 9 7900 is essentially the 7900X without PBO enabled, but it would be a waste to spend more money on essentially the same chip to then underclock it for better thermal performance. It's a better value choice to pick up the Ryzen 9 7900 and then boost up to 7900X-level performance through a simple BIOS toggle. After this has been carried out, performance is pretty much identical.” Some more reading fodder: https://www.anandtech.com/show/18693/the-amd-ryzen-9-7900-ryzen-7-7700-and-ryzen-5-5-7600-review-ryzen-7000-at-65-w-zen-4-efficiency [0] https://en.wikipedia.org/wiki/Haswell_(microarchitecture) [1] https://en.wikipedia.org/wiki/Alder_Lake [2] https://en.wikipedia.org/wiki/Zen_4 -- Grüße | Greetings | Qapla’ Please do not share anything from, with or about me on any social network. “If privacy is outlawed, only outlaws will have privacy.” – Phil Zimmermann
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