-2

Background: I am shopping for processors to build a server on Newegg.

The first bullet point on each processor displays the size of the chip in nm and its wattage. Why?

I am looking at the number of cores, clock speed, cache, socket type (for mb), branch predictor (& assoc. architecture), etc.

Question: What is the substance in showing the size of the chip and wattage? What should I focus on with these values?enter image description here

MadHatter
  • 79,770
  • 20
  • 184
  • 232
Chris
  • 149
  • 5
  • 1
    The wattage tells you how much you will be paying on your energy bill, and strongly indicates how much heat you will be generating, and will tell you how good of a cooling system you need.. The nm value probably doesn't matter to 99% of the population, and you can ignore it. – Zoredache Feb 06 '13 at 01:24
  • Why -1?? Is this the wrong forum for asking such a question? – Chris Feb 06 '13 at 01:34
  • I didn't downvote you, but it is off-topic here for one. How do you think it is related to professional systems administration? – Zoredache Feb 06 '13 at 01:35
  • Good to know! I thought this forum included h/w aspect of servers too based on others posts on processors... Thank you for clarifying – Chris Feb 06 '13 at 01:38
  • 1
    @Zoredache on second thought, how are server processor stats not related to prof sys admin? Shouldnt we know specifcs about the h/w running our s/w? Is discrete h/w knowledge not part of a professionals admin tookit?? – Chris Feb 06 '13 at 01:53
  • These are not processors that would normally be used in _professional_ servers. – Michael Hampton Feb 06 '13 at 02:14
  • Thank you yes, but it was clearest image I could find that 'showed' what I was asking... So if it were images of E5-2690's THAT would then be acceptable?... – Chris Feb 06 '13 at 02:24
  • 1
    But why does it have to be about servers? Have companies stopped buying desktops for their users? This question is perfectly valid for a professional setting. If I'm about ready to purchase 500 desktop computers from dell and these are the different processors I can choose from, then yeah, I'm going to want to know the specifics about the Wattage and size of the chip(well, maybe not so much the latter) – Safado Feb 06 '13 at 03:56
  • The response and downvotes here are probably because professional administrators tend to evaluate these types of things using different metrics; Current processor generation, price, performance needs and the server/workstation vendor offerings. I don't know many sysadmins who still *build* systems from scratch. – ewwhite Feb 06 '13 at 10:12

2 Answers2

8

Broadly speaking: You don't care.
What you probably care about when designing a server is speed (GHz), parallelism (number of cores), and bus speed, combined with the total heat load (usually expressed in BTU/hr) the machine is going to put on your cooling system.
How you prioritize these depends on your use case.

If you care anyway:

Wattage (more accurately "Wattage - Thermal Design Power") is probably the number you care about: It's a statement of the amount of heat the CPU will produce when working, and how much electricity it will need.
CPUs with a higher wattage rating will consume more power, and generate more waste heat - this drives up the cooling load (and power demand) for your datacenter.

The nm (nanometer process - reflecting the size of elements on the chip) number affects both chip speed and power usage (wattage) - in the most general terms, smaller chips (lower numbers) are faster and more power efficient. (If you've ever seen Grace Hopper explain nanoseconds, the concept translates: smaller elements mean faster machines - though you're also benefitting from miniaturized transistors that switch faster, the ability to cram more of them on a chip, etc.)

Further Reading:

voretaq7
  • 79,879
  • 17
  • 130
  • 214
  • Wattage is very important - not only are power prices rising, but more power usage means more expensive UPS kit needed and less runtime to be had from it. – rackandboneman Feb 06 '13 at 07:54
  • @rackandboneman this is true, but if you're looking to reduce power consumption there are other places I'd look before the CPU (like swapping spinning disk for SSDs). Unless you're talking 4 CPU machines or diskless systems the power to keep two or more disks spinning is a substantial percentage of the system's overall current demand. Everywhere I've worked tends to run out of cooling before running out of circuit/UPS capacity :-) – voretaq7 Feb 06 '13 at 16:12
  • I did a couple measurements in the past, the power consumption of disks appears to be overrated - you hardly get even fast disks anymore that draw more than 10W each. – rackandboneman Feb 07 '13 at 07:01
4

nm is actually more of a reference to the generation of manufacturing process; a chip made with a 22 nm process will be more modern than a chip made using a 32 nm process.

Wattage is especially important in servers that serve more than one cpu on the motherboard; if you're sporting a 64 cpus, you'll only have so many watts available to each core, depending on your motherboard specs.

Stephan
  • 999
  • 7
  • 11
  • And on a more minor note, you can only use as much wattage as your power supply will allow. So you have to take into account not only the wattage of your CPU, but also any other device you're connecting to it and stay within what your power supply can handle. – Safado Feb 06 '13 at 04:05