Question: I just realized that the directions in "UPload" and "DOWNload" seem arbitrary to me as a non-native English speaker. I took a look at a couple of dictionaries and they said that this word is a result of merging "down" and "load", which doesn't seem to explain anything. Where could those two directions come from?

Answer: 
OED noticed the word for the first time in 1976, it seems.

1976 was very early in the development of computers. FTP (File Transfer Protocol) was designed 1971 and TCP/ IP followed in 1973. These two protocols made any transfer of data possible for the first time.

Servers or internet wasn't something anyone could imagine yet. Instead scientist were still hammering out the basic how of a data transfer.

In these years, several conceptual models for the transfer of data were developed. Most used and known nowadays is the OSI model with 7 layers - and these layers have an up / down direction.

Now, if I want to get data from another computer, I technically send the other computer a request, which then converts said data "down" to the physical layer, until all is left is a physical signal. This signal is then send to my computer, and I convert it again (this time "upwards").

This also is a likely explanation why "upload" appeared years later, in 1980 according to OED. Upload was coined as the simple opposite of download.

Though, while this is what I first thought of, it might be that there is also a hierarchy meaning in play as well.
Download and Upload are far from arbitrary, they are entirely rational:

A **[Download](https://en.wikipedia.org/wiki/Download)** refers to data that is brought '**down**' from a network, the World Wide Web (Or Cloud) to reside on a local drive / computer.

**Upload** is data that is sent '**up**' to the World Wide Web (Or Cloud) from a local drive of computer.

The term originated as others have described from the pre-personal computer era, and is a Networking term.

In the good o'l days [1970's],all computing power was housed exclusively in remote Server or mainframe computers - it was too expensive for an individual to buy. 

Other than a local terminal directly wired to the 'glowing mass' of the mainframe, any other connections were "*Down the wire*", outside of a large company with a LAN, typically this would be the public telephone system. I remember visiting my Secondary School during the summer holidays in 1977 to play "Lunar Lander" via the dial-up telephone-cradle modem link to the local council mainframe computer.

[![1970's Cradle modem](https://i.stack.imgur.com/gDmHv.jpg)](https://i.stack.imgur.com/gDmHv.jpg)

As an aside: The game required the player to type in a numerical value, which was sent 'up' the telephone line to the mainframe, which would respond to the teleprinter with a message like:

> 
> "You are at 3,000' and descending at 50m/sec."
> 
> 
> 

The player would type another value and so on until you received the message:

> 
> "Congratulations, you have crashed!"
> 
> 
> 

Tv monitors and video displays were but a distant dream...

All local drives were "down the wire". 

Any keyboard inputs were sent "up the wire"...

See also: [Downstream](https://en.wikipedia.org/wiki/Downstream_(networking))