Wikipedia:Reference desk/Archives/Computing/2022 July 11

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July 11

Simple OS

I would like to experiment with the branch prediction of my CPU. For this I need to measure its performance. Unfortunately, almost all modern OSes use many processes and actually preempt processes very frequently. This of course can lead to very poor measurement accuracy. I look for a simple OS: a kernel that let few process to run, and a shell of course I can use to run the experiments. Alternatively, I look for a kernel that let a process to get an exclusive CPU time till the experiments ends, without interrupting the measurement. Thanks Exx8 (talk) 15:55, 11 July 2022 (UTC)

If you are using Linux or another UNIX-like OS, you can (as a superuser) issue "nice -n -20 command", which gives it a higher priority than any background tasks. If you boot to runlevel 1, you are in single-user mode and no daemons will be fired up. Alternatively, shutting off all connections to the Internet and external devices may also help.  --Lambiam 17:43, 11 July 2022 (UTC)

Lowering your nice level will give your process higher priority but won't completely stop other processes from running, especially kernel processes. Similarly, booting to single user mode will cause most user-space processes to not start up, but won't prevent kernel processes from running. For example, when I boot my Fedora system in single-user mode, there are still 320 kernel processes running. Most of them will be idle if you're just running a single compute-bound user process, but there's no guarantee that your process won't lose the CPU for brief periods.

For low-level tests like this, you'd probably want to run a real time OS like VxWorks. It's been a number of years since I've used VxWorks but I remember it being pretty good. We have a list of real time OSes here. CodeTalker (talk) 23:32, 11 July 2022 (UTC)

While most modern operating systems support some form of multitasking,

for this experiment it sounds like you want a single-tasking single-process OS such as FreeDOS, ILIOS, eCos, etc. or perhaps a Unikernel such as IncludeOS. --DavidCary (talk) 16:19, 17 July 2022 (UTC)

I have a question about tablets

I live in Canada and there was/is a network outage in Canada through Rogers. I currently can use internet and my phone right now. And if I download movies on my tablet would I be able to watch those movies if there is a network outage though Rogers again? I'm sorry. I don't know the answer to this question as I'm not good at technology and I'm disabled. 2001:569:7D9A:1300:50CF:A6BD:7389:71E1 (talk) 17:32, 11 July 2022 (UTC)

You should always be able to watch already downloaded content, also without network connectivity. If a film has not been downloaded but is streamed, it arrives via the network to your device as you watch, and in that case network outage means the stream comes to a halt.  --Lambiam 17:50, 11 July 2022 (UTC)

As Lambian said, once a file is downloaded, it's there to view whenever you want. For example, with apps like Netflix and Disney+, you can download files to your tablet and they'll stay there indefinitely and you don't need internet access to view them. I know it works for them because I've tried it, but other platforms may do things differently. If you have a particular service in mind, we could provide more accurate information. Matt Deres (talk) 23:58, 11 July 2022 (UTC)

If the film is downloaded, then even God Himself could not prevent you from watching it. If you are expecting a network outage, then downloading movies is a really good idea. Pablothepenguin (talk) 18:56, 12 July 2022 (UTC)

No, but digital rights management might. Example: I borrow a digital book from the library, download it to my e-reader, then take the reader offline. I can read the book with the reader offline, but three weeks later my loan expires and I can no longer read the book (independently of whether the reader is online or offline). Mitch Ames (talk) 23:50, 12 July 2022 (UTC)

Yes, something similar happens when Netflix removes a show from their library; it being downloaded on my tablet doesn't save it, though the deletion might only occur if there's a connection; it's hard to say. Matt Deres (talk) 12:56, 13 July 2022 (UTC)

While I don't know the specifics of Netflix and Disney+'s app, I strongly suspect they need periodic connection to keep being able to play even downloaded content. This may not be very frequent, but I somewhat doubt you'll still be able to play content if they haven't connected in several months. I suspect this will be the case even if your subscription was due to laster longer than that. But definitely I don't expect downloaded content to still work much beyond the end date of your subscription that the app received last time it connected. (And to be clear for auto-renewing monthly subscriptions, this will be when the subscription runs out for the month if not renewed.) If you fool around with the date, you might be able to bypass this, OTOH, if you aren't careful you might trigger a need for reconnection even if the app would have worked without it. (Purchased content in theory may be playable indefinitely even without ever needed to reconnect but I don't believe either services allow you to purchase content but instead are totally subscription based.) Nil Einne (talk) 13:22, 13 July 2022 (UTC)

Yes I found this for Disney+ which says 30 days [1]. For Netflix, it seems it's even more limited, most downloads only last 7 days and expire 48 hours after you start watching [2]. Nil Einne (talk) 13:37, 13 July 2022 (UTC)