Whatsapp don't retain messages/media after they've been delivered to your phone, which is a compelling privacy feature for many.
It's also what allows them to serve such an enormous user base with limited hardware. Their technology stack (FreeBSD/Erlang) is pretty interesting, more info here:
2014 talks by Rick Reed:
https://www.youtube.com/watch?v=c12cYAUTXXs
https://www.youtube.com/watch?v=TneLO5TdW_M
Slides:
http://www.erlang-factory.com/static/upload/media/1394350183...
There's likely no technical reason why you couldn't use a pc instead of a phone for users that want to use the pc as the primary client (with the phone optionally accessing the DB on the pc in the same way that the desktop client does for the phone). Perhaps they've decided that this is a small and declining market.
Edit:
Slides for second talk
http://www.slideshare.net/iXsystems/rick-reed-600-m-unsuspec...
440k connections/sec, 1.1 million msgs/sec, 1 billion images/day, and that was in 2014...
Any personal computer built in the last five years can do anything a smartphone or tablet can in terms of processing power and connectivity. A smartphone is a computer with hardware that enables it to use cell phone networks and make calls.
My inner cynic strongly suspects that Facebook and other similar corporations really like the control they have on the overall user experience on the two major mobile operating systems; i.e., eyeballs on a smartphone or tablet are worth more than those on a general purpose computing device.
Too much freedom on a personal computer; with browsers that feature all kind of privacy enhancing add-ons such as ad-blockers and tracker-blockers. Much harder to monetize.
So are you saying that a desktop PC's hard drive can't handle storage of some text messages but a phone can?
For consumers (and facebook is a consumer company) it's all about who owns mobile (and can also compete with facebook). They want desktop to just be enough of a feature to be more appealing than other platforms, but not enough that it detracts from mobile.
Imagine a scenario where you were to get rid of the phone number and had sessions open on the desktop and the web. WhatsApp servers have no way of knowing where the phone number went or if it will be online ever again or if you continue to own the phone number, or someone else owns it. They need to route the msgs through that phone/number combination all the time, because it's the single source of truth.
Its security and privacy that's preventing them from providing the feature you're asking for.
If they detach individual user's identity from a phone number, may be then they can be a true cross platform (web, phone, desktop) messaging app.
Another advantage of using phone numbers is that people actually have other people's numbers in their phone address books, which whatsapp uses. Very few people have their friends' email addresses on their contacts.
Being able to sync across all your devices requires they start storing all of your communications centrally, which defeats the whole information security model.
But i found whatsapp is next to mp3 in my and my friends phone so it is not easy from bandwidth perspective
Or home phone numbers (landlines) for that matter. Let people use a landline number on a tablet.
The only problem I recall is that the initial text verification doesn't work - I had to do the phone call option - but this is a problem with gvoice, not WhatsApp: google blocks pretty much all server-triggered texts.
I don't have the slightest idea on how to fix it. The only reason it worries me a bit is that I might miss texts from other people.
Switched to an iPhone so I could use "Find Friends" with spouse and kids.
Whatsapp makes you to stay connected at the same time on your phone to use their web/desktop apps.
It seems that was the main reason people didn't like Jabber to start with.
I haven't analysed any traffic and I'm not a developer but my layman's guess would be that the WhatsApp mobile app has a pre-prepared Zip file (or some other compressed container) with the 20 most recent messages from each chat plus these compressed image thumbnails and the Web Client pulls that data from the phone upon initialising. I doubt it is a big data transfer.
Using mitmproxy to snoop my phone, I see that all the data coming into my computer when I open up Whatsapp Web is originating from my phone. Including pictures.
That being said, all of my current conversations are on the new "end-to-end-encryption" thing, which might make a difference.
You can test this by trying to download an image for the first time after a few weeks, it will tell you that the image is no longer available, and you should ask the other recipient to send it again.
The time Whatsapp web takes to download images and messages is far way faster than my actual 2G network on phone.
WhatsApp managed to load all my conversations (I don't have many) and the most recent message, for display in the list-view. But each conversation only has the most recently sent message. After a while I got a "Phone Not Connected" message. Seems like it really is only stored on your phone.
Yes, that's why I think so. They easily loads all the messages and images in just few seconds even when my phone's internet is too slow.
They won't let you use the web app when you're phone is disconnected, so there's no way to confirm it.
Your phone has the data on it. Intranet speeds on most wifi networks these days is faster than 50Mbps. That's more than fast enough to transfer all your messages and photos with little to no lag.
It doesn't matter how fast your connection to the WWW is because you're not using the WWW to transfer the data, you're using the wifi intranet.
That makes it easy to send all the data necessary from your phone to your computer in the blink of an eye, because intranet wifi speeds are very fast.
On my iPhone, backups can be stored, but through iCloud, not on Whatsapp servers.
You need a phone number just to create an account first, you can turn it off after that.
You can send messages to all of your facebook friends through facebook.com on any device, as you always could.
most likely their internal system can only think in telephone numbers or something like that
If the Whatsapp team actually tracked the rate of user engagement with these Desktop/Web editions & compared this to the Smartphone/Tablet apps. They would agree with you.
Surely you are talking about them tracking the rate of user engagement across their userbase, not just the data of you alone?