Wikipedia:Reference desk/Archives/Computing/2016 February 18

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February 18

Adding memory

We have several computers around here, i5s and i7s. The manual on most of them say that they can take four 4GB DIMMs. One of them is a HP 8200 Elite SFF i5-2400. The manual says that it can take four 4GB DIMMs but the Crucial and Kingston websites say that it can take four 8GB DIMMs. I don't think that any of the others are like that. Will a computer designed for 4GB DIMMs generally support 8GB DIMMs? Bubba73 ^{You talkin' to me?} 00:29, 18 February 2016 (UTC)

I suppose it will be a waste of resources, since your computer won't be able to address the bigger RAM. I'd stick with the official manual, and not follow Crucial or Kingston advise. It won't toast your motherboard though. Maybe the computer just does not boot. --Scicurious (talk) 00:48, 18 February 2016 (UTC)

I will respectfully disagree with the above. It's unlikely the system won't be able to "address the memory space" (assuming you are using a 64bit operating system, which anything using over 4GB total should be anyway). Motherboard manuals TYPICALLY will list the 'supported' memory, this means the manufacturer has performed stress tests and compatibility tests with THOSE specific memory chips. It does NOT mean that other memory will "not" work. In fact, if when the motherboard came out, 4GB was the biggest RAM chip you could get, it's quite likely a motherboard manufacturer will not bother to go back to test an old board just because 8GB sticks are now available (it's not likely to sell them any more old motherboards, if in fact they are even still for sale). CONVERSELY when a new memory chip comes out, it IS in the interest of the memory manufacturer to make sure that their chip works with as many mother boards as possible (that WILL sell them more memory chips) so they quite probably WILL test older motherboards with their new chips. SO, if kingston or cruicial say their chips will work with your motherboard, I would very much take their word for it. Vespine (talk) 03:19, 18 February 2016 (UTC)

I will respectfully disagree with your respectful disagreement. RAM limit (Wikipedia:WHAAOE) depends on other factors too. There is a CPU addressing limit. There is no reason to have a CPU able to address more memory for no reason. The 64bit OS is indifferent here. More lines are simply not wired to the memory controller.Scicurious (talk) 16:28, 18 February 2016 (UTC)

I mostly agree with Vespine here. It's true there's no guarantee that a larger RAM size is going to work. Although this rarely has anything to do with lines not being wired to the memory controller, but instead what the memory controller supports, the CPU (seperate from any IMC), the actual DIMM design (for most forms of DDR sticks there can generally be multiple types of 8GB RAM sticks with different levels of compatibility) and sometimes also BIOS/EFI issues. Motherboard manuals are not always reliable on what the motherboard actually supports and in this case the memory controller is on the CPU which supports up to 32GB [1] although Intel hasn't really kept their sockets around for very long recently and I'm not sure if there was ever any real difference in IMC supported amount of RAM. (But it's only dual channel and AFAIK it's not really possible to support more than 2 sticks per channel on an LGA1155 platform which implies it must support some sort of 8GB sticks.) Anyway, if a major RAM seller is claiming that a major system does support their 8GB sticks, it likely does since most RAM sellers like these do provide some sort of money back guarantee so they tend to try and get that stuff right and it's likely someone has already tried it. If it's a fairly unknown system or a weird config, it's possible the info from the RAM seller could simply be wrong, but probably not here. Nil Einne (talk) 17:12, 18 February 2016 (UTC)

Mind you, while I have no idea what manual the OP is looking at, this manual for the same system explicitly mentions 8GB stick support [2] "The largest memory capacity possible is 32GB using four (4) 8GB DIMMs". It doesn't list 8GB sticks in any of the sample configs, probably because 8GB sticks suitable for a system like this (i.e. unbufferred) didn't really exist when it was written or if they did HP Compaq didn't sell them as standard components but it's obviously at least claiming theoretical support. Nil Einne (talk) 17:20, 18 February 2016 (UTC)

That is the document at which I was looking, but I missed that line. I was looking in the table on page 12 where it shows 16GB maximun. Bubba73 ^{You talkin' to me?} 20:48, 18 February 2016 (UTC)

Indeed, the whole issue is probably not a big deal. Crucial's forum already has a post about it: [3]. It is almost sure a case of a not updated manual (in OP's hand) vs. the updated DB of Crucial. That's also why Nil Einne found the figure of 8GB when he looked it up. — Preceding unsigned comment added by Llaanngg (talk • contribs) 18:44, 18 February 2016 (UTC)

How can I watch Hulu In Canada?

Please tell me. 208.181.190.136 (talk) 03:23, 18 February 2016 (UTC)

Use a VPN. --Scicurious (talk) 16:31, 18 February 2016 (UTC)

In other words, there is no non-technical way to do so. Hulu is not officially available in Canada. Mingmingla (talk) 01:53, 19 February 2016 (UTC)

Using a VPN is no longer a guarantee at all that a regional online streaming service will work, or will continue to work. Most such streaming services, including hulu and netfix, explicitly forbid using VPN services to bypass regional restrictions in their terms and conditions and DO enforce various levels of blocks and bans against users who they discover or detect using such services. Vespine (talk) 03:19, 19 February 2016 (UTC)

out of range

am trying to install Win 7 on a Pc its P4 but wen i press the boot frm cd room key, a message Resolution not supported comes out on another moniter a message Out of range pops up,wat do i do? — Preceding unsigned comment added by 197.79.9.249 (talk) 11:48, 18 February 2016 (UTC)

Sounds like the monitor doesn't support the screen resolution it uses for the install. If you have another monitor, you might try that. StuRat (talk) 18:27, 18 February 2016 (UTC)

I think so. Temporary use another monitor and change the screen resolution and refresh rate manually. --Hans Haase (有问题吗) 18:24, 22 February 2016 (UTC)

Macintosh LC

Why was the Macintosh LC a significant product of technology in 1990? Please write up to 3000 words explaining your answer and submit your paper by 03/03/16 to Mr Turnbull's office. --Finderoomertæs (talk) 17:39, 18 February 2016 (UTC)

Remember to provide references and sources. --Finderoomertæs (talk) 17:40, 18 February 2016 (UTC)

We can't tell if you're being facetious - but we will not do your homework. We will gladly volunteer our efforts to help you, though. Some of our reference desk researchers might even, you know, be good resources. Nimur (talk) 17:51, 18 February 2016 (UTC)

We have Macintosh LC, I think... --Stephan Schulz (talk) 22:44, 18 February 2016 (UTC)

I've finished and submitted the paper. The response I received from Turnbull's office was that they had no idea why I sent them a paper on the 1990's significance of the Macintosh LC but if I did it again Turnbull will ask Key to pull my pony tail. Not wanting that, I've deleted my paper. Nil Einne (talk) 18:05, 19 February 2016 (UTC)

I only read "I have a pony tail" - that's surprising new information! --Stephan Schulz (talk) 09:18, 20 February 2016 (UTC)

Our RD powers do enable us to identify the OP's Mr Turnbull - his office is number 3xxE. Not that we would reveal the value of "xx", of course. Tevildo (talk) 10:47, 20 February 2016 (UTC)

Why does the FBI need Apple's help?

Being the FBI in possession of that iPhone, couldn't they just clone it bit by bit, literally, and test passwords on each clone? Obviously there is something here hindering this, but what is it? How can a storage medium block being copied? --Llaanngg (talk) 20:22, 18 February 2016 (UTC)

The Register has some well-informed speculation. [4] ---- LongHairedFop (talk) 20:27, 18 February 2016 (UTC)

That might be a good overview, and there's another one above in this same page. However, the question is more about storage hardware that does not let being copied 1-to-1. I wonder how this is possible. Couldn't they just disassemble the device and read the storage with another controller? --Llaanngg (talk) 20:32, 18 February 2016 (UTC)

iPhones use whole-disk encryption, which is protected by the user's passcode. Even if the flashdrive is copied to another iPhone, it is useless without the passcode. LongHairedFop (talk) 21:53, 18 February 2016 (UTC)

If you can copy the flashdrive to other iPhones, you could test more passwords on them (which are 4-6 numbers long). But there is obviously something that makes this impossible. --Llaanngg (talk) 21:56, 18 February 2016 (UTC)

In short, there is some piece of hardware that is designed to be difficult to clone, which holds a secret, and all other data is encrypted with a key derived from that secret. In most computers that hardware would be the TPM. In the iPhone 5c it's (a part of) the Apple A6 SoC. The A6 likely authenticates the first-stage boot code (which authenticates the next stage and so on), meaning there's no way to run unsigned password-forcing code. Even if it doesn't, it would probably be risky to inject a modified first-stage boot loader into the irreplaceable phone. -- BenRG (talk) 23:04, 18 February 2016 (UTC)

Llaanngg, the passcodes on iPhones can be longer than 4-6 characters. Even if the limit were 4 numbers, that's still 10,000 different passcodes that it could be. That's either a lot of iPhones that the FBI would have to buy (assuming that copying everything over to a different phone is even possible) or a smaller number with a lot of erasing of failed phones and reloading of the data. Dismas|^(talk) 00:00, 19 February 2016 (UTC)

The newer models have longer passwords, but in this case it is a iPhone 6, which has passwords which are 4-6 numerical characters long.

If it were possible to erase and reload the information to a new phone, the question would be how long would it take to accomplish this reset. You can try 10 passwords until the phone deletes the information. So, in worst case 1,000 load, erase and rinse cycles. But apparently some piece of hardware was made difficult to be cloned. Llaanngg (talk) 00:12, 19 February 2016 (UTC)

I wonder whether it might be worth saying that "reading" a memory chip is unlike reading a hard disk. You can't just point a read head at it and extract the bit values one by one. In silicon memory, you have to rely on the (usually) integrated memory controller to read and write values in and out of the memory. The memory controller has its own firmware which can be as "open" or "locked" as the designer wants. Clearly in the case of the iPhone, it's quite "locked" down. The difference is that Apple could us a special digital signature that only they have to load a special firmware during boot up before the phone normally lets anyone run any code. Vespine (talk) 00:19, 19 February 2016 (UTC)

Yes, this is surely worth (at least for me). Llaanngg (talk) 00:22, 19 February 2016 (UTC)

Just a nit but it's actually a iPhone 5C as pointed out in the first link in this section. But it could still have the latest iOS on it. Dismas|^(talk) 00:26, 19 February 2016 (UTC)

Yes, you are right. Anyway, it was not the last model. Llaanngg (talk) 00:34, 19 February 2016 (UTC)

To expand on what I believe BenRG was saying, each phone has a hardware module that stores a unique key. The disk is then encrypted using a combination of that unique key and the user's password. It shouldn't be hard to copy the physical contents of the iPhone storage, but trying to decrypt those contents without the corresponding hardware module is much harder than trying all possible 4 or 6 digit passcodes because you also have to consider all possible versions of the unknown hardware key. I don't know how long the unique hardware key on an iPhone is but the computer equivalent TPM has a built-in 2048-bit (256 bytes) hardware key. Trying to decrypt the storage without the hardware key would be far harder (virtually impossible) so one pretty much has to use the same phone to decrypt its contents. Dragons flight (talk) 18:15, 19 February 2016 (UTC)

To expand a little more - that key comes in part from a number that's burned into the chip when it's manufactured - and that's done in a way such that neither Apple nor the chipmaker retain any information about which numbers were used in which specific chips. Another part of the number comes from a cryptographically sound random number generator - which is also impossible to obtain from outside the chip. So a brute-force decryption of the memory chip is the only route - and with a 2048 bit code...that's not going to happen.

The only practical way to hack the phone is to send it an "operating system upgrade" that circumvents the memory erasure process after ten failed password attempts. Then brute-force password testing of a 4 to 6 digit passcode becomes easily possible. But Apple went to great lengths to 'sign' their upgrades in such a way that other people wouldn't be able to produce malware as operating system upgrades...so the FBI can't go that route without Apple doing the work and pushing out a new OS to that phone. I believe that Apple's concern is that once the FBI have that fake upgrade on hand, they'll be able to apply it to other phones. SteveBaker (talk) 17:07, 23 February 2016 (UTC)