Wikipedia:Reference desk/Archives/Computing/2014 December 19

= December 19 =

thermal compound/paste
thermal compound/paste is there any other alternative to replace it.can it be made by youself.if can,how?:Q — Preceding unsigned comment added by 219.94.83.162 (talk • contribs) 01:50, 19 December 2014‎


 * There are a couple of possibilities discussed here - a toothpaste/Vaseline mix, and a diaper rash cream. Neither appears to be anything but a short-term makeshift substitute, and I'd certainly not recommend either unless you are prepared to risk destroying the CPU or whatever if they fail. Thermal grease is expensive, but not as expensive as using something cheaper that doesn't do the job properly. AndyTheGrump (talk) 02:17, 19 December 2014 (UTC)

Andriod/iOS devices
Why are mid to high end tablets so much cheaper than phones with similar specs and capabilities. From what I understand, the only major hardware missing from tablets still is the cellphone radio (for WiFi only models), since most high end tablets include the motion, light, and GPS sensors. They also usually have bigger batteries. It just doesn't make sense.
 * Well if the specs are entirely the same, then you have far more room to work with in a tablet. Of course a bigger battery, larger screen and case would generally cost more than a smaller one, although for the screen, resolution and other factors will come in to play. Nil Einne (talk) 15:40, 19 December 2014 (UTC)


 * I've failed to find actual dimensions, but looking at disassembly videos of the various iPhone and iPad devices (neglecting the iPad Air) they're build to much the same format - they have a main logic board that's about 40mm wide that runs on the side (the long axis) of the device. The battery sits beside that, and the display sandwich is above both. So it looks like the phone PCB is about half the area of the tablet ones - with, as you say, about the same hardware on it. Making very small footprint, dense boards like this is expensive - generally you need more layers, more blind and buried vias, and in general more tortuous feats of routing. Again I can't find a reliable source, but it looks like iPhones have something like a 10 layer board and iPads a six layer board, with the iPhone using thinner traces and smaller vias. So the logic boards are pricier to fabricate - but by how much, only Apple and their partners know, and I don't think it's enough to explain all the differential. -- Finlay McWalterᚠTalk 16:20, 19 December 2014 (UTC)


 * This story in EE Times talks about the 10-layer package-on-package board in the iPhone 4. It confirms what I've said about small traces and laser-drilled microvias. They put the price of that board at $5 (from maybe $2 for a simpler board) - so that doesn't remotely cover the differential you're asking about. There will be additional costs to stuffing such a complicated board (particularly the package on package components) - but I've no idea how much. The very dense nature at which ICs are packed will have two additional problems - thermal and EM. All these chips right next to one another, or actually stacked, means that the phone form factor will have a harder job dissipating heat into heat spreaders or the casing. The EM problem is due to the proximity of various RF systems (GSM/GPRS/HSPDA, Bluetooth, NFC, WiFi) - if they're in extreme proximity to other components, they may interfere. A tablet has a bit more space to get these (particularly their antennas) away from the digital logic and from one another.  It seems the iPad Air, and some iPhone models, has an L-shaped extension to the main PCB (or a RF daughterboard connected to the main logic PCB with a flexcircuit), which allows them to put some distance, and some of the battery, between the antennas and the main logic. -- Finlay McWalterᚠTalk 18:42, 19 December 2014 (UTC)


 * Without getting into the technical details of electronics (as the others have presented well), consider a few related questions - why was a laptop in 2000 significantly more expensive than a comparable desktop PC? Or in the 1960s, why was a portable radio much more expensive than a desk model? Making item A to have similar performance to item B but much smaller is almost always more expensive. Engineering is much easier when space and weight are not restrictive. Even today, a mid-range mechanical watch is more expensive than a mid-range mechanical wall clock, and the same goes for quartz clocks too. SemanticMantis (talk) 18:10, 19 December 2014 (UTC)


 * As to materials - some educated estimates of the bill of materials for the iPhone5 put that at $199-$230 and for the iPad Air 2 at $275 - $358. -- Finlay McWalterᚠTalk 20:14, 19 December 2014 (UTC)
 * And in case people are wondering, the iPhone 6 or even 6 Plus isn't that diferent . Nil Einne (talk) 01:33, 20 December 2014 (UTC)


 * Just a guess, but I'd suspect Apple, at least, makes more money back from app store purchases for iPad than iPhone. They're not just selling the hardware, they're selling the platform. Horselover Frost (talk &middot; edits) 16:06, 20 December 2014 (UTC)