Wikipedia:Reference desk/Archives/Computing/2018 May 21

= May 21 =

Twitter
I'm getting old in the tooth and is having a lot of trouble operating this new fangled "Twitter" thing that's so hip nowadays.

1. Someone told me to "PM them on Twitter" and gave me their twitter username @JohnSmith (for example).

2. I sign up on Twitter, opening the PM tool, type in their username and my message, but is told: "This user doesn't follow you. You can only send messages to people who do." What's going on here? Did I do something wrong or does the person block all messages or something?

3. With no way to PM them, my last resort would be to tweet at them. So I tweet "@JohnSmith I'm trying to PM you but can't. You need to check your settings." Now I'm on a brand new Twitter account, so obviously @JohnSmith isn't following me. Will @JohnSmith even be able to see my tweet? Are Twitter users automatically notified when their username appears in a tweet? Or does that depend on their Twitter settings again? Or is there some special syntax I need to use in order to "poke" them? Mũeller (talk) 03:23, 21 May 2018 (UTC)


 * Twitter calls them DMs (direct messages) not PMs. I mention this because it could be helpful in searching for help etc. Anyway Twitter by default only allows people to send DMs if the recipient is following the sender or the recipient has sent the sender a DM before. [//help.twitter.com/en/using-twitter/direct-messages] [//help.twitter.com/de/using-twitter/direct-messages] An exception is if the recipient has chosen to accept DMs from everyone which very few do. If someone isn't following you and don't accept DMs from everyone your best bet is to Tweet at them in the manner you mentioned. It's best if there is nothing before the @, simplest is to use the "Tweet to" whoever button on their page e.g. "Tweet to Ragnar Tørnquist" [//twitter.com/ragso] and then type your tweet after what appears. They will probably see it, but may not. Ultimately as with most things in life, there are no guarantees. It appearing on their feed doesn't mean they're going to notice it for example. You can only try and hope for the best. Nil Einne (talk) 07:42, 21 May 2018 (UTC)
 * Thanks!
 * When did this "not able to receive DM from stranger unless you explicitly enable it" change happen at Twitter? Mũeller (talk) 09:29, 21 May 2018 (UTC)
 * Are you sure it's a change? My impression is it's always been like that. At best, I think a lot of people don't know of it simply because they rarely use DMs on Twitter. Twitter has always been the oddball of social media which had somewhat of a focus on interaction with random particularly famous people and less of a focus on friends & family. And especially with the length of message limit (even if that hasn't applied to DMs for a while), it's not really seen as a place for long conversations. And despite recent attention particularly in the US due to the use by the US president, I think a lot of people either don't use Twitter at all, or just use it to e.g. see what famous people they follow are saying or for breaking news especially before it hits the news media. (It's often said people especially younger people are turning away from Facebook, but this is in more of a different way.) So DMs are just an odd-ball addition to an oddball platform. I suspect their most common usage is probably to interact with businesses when someone is complaining about some issue. The standard response to complaints is often either 'we've DMed you' or 'DM us or follow us so we can DM you'. Nil Einne (talk) 03:53, 22 May 2018 (UTC)
 * Found [//www.npr.org/sections/thetwo-way/2015/04/20/401020521/twitter-now-allows-users-to-receive-direct-messages-from-any-user] which suggests it's the opposite. It wasn't possible to allow strangers to DM you until ~2015. Nil Einne (talk) 03:54, 22 May 2018 (UTC)

Analogue vs digital magnetic tape track width
Hi. There's a wealth of information online (both on WP and elsewhere) on the growing areal density of computer magnetic tape (which is the product of track pitch and linear density). Long story short, it tends to follow HDD trends with a lag of about 10 years. But of course, the total area of a reel of tape is much larger than that of a few HDD platters, which is why people keep using them when they need to store a s***load of digital data. Now of course, linear density (measured in kilobits per inches) isn't applicable in any simple way to analogue audio or video tapes, but track width is. I haven't been able to find anything online about the narrowest track width used in analogue tape. Using different read-write head technology, tape material with higher coercivity, and so on, it must be possible to fit the same bandwidth in a smaller area. Can someone help me out, direct me to some sources? Thanks :) — Preceding unsigned comment added by JaneStillman (talk • contribs) 16:13, 21 May 2018 (UTC)
 * Compact_Cassette states the track width as 1.5 mm for mono recording or 0.6 mm for stereo recording. A smaller track width would give a weaker playback signal and therefore a poorer (smaller) Signal-to-noise ratio. DroneB (talk) 23:22, 21 May 2018 (UTC)
 * Wire recorders using a finer medium (0.10 to 0.15 mm) and SEAC used wire recorders to store data. I don't know why magnetic type was more widely used. Cost maybe? --TrogWoolley (talk) 13:39, 22 May 2018 (UTC)
 * A major breaktrough was discovering the Giant magnetoresistance (GMR), which allows to focus magnetic fields. I guess the the 2 GB HDDs the GMR technology came into the data heads in the drives. Former magnetic recording did not use this technology. Also cobalt based magnetic coatings of tapes did not reach the marked due assumed costs. Also several mechanic technologies with minor effects have been used to keep the tape lined up on the heads. Hifi or acceptable quality of analog recording required a bias on the heads to fight remanence. A later figured pulse-width modulation on analog recording made the bias obsolete like on digital recording, a bias never was needed. Without GMR, the higher spreading affected the magnetic material near the head. -- Hans Haase (有问题吗) 15:51, 24 May 2018 (UTC)
 * A consumer VHS deck could use as small as 0.03 mm head with a 0.02 mm track for the highest density (Extended Play or EP). And they made hardware for backing up your computer on VHS, storing 4 GB on a tape. So areal density (computer storage) was (4 GB) / ((247 m) * 12.55 mm) = 1.29038502 × 109 bytes / m2 = 6 660 038.39 bits / in2 or about 6.7 Mbits/in2. StrayBolt (talk) 16:42, 27 May 2018 (UTC)