Is this sale considered valid and does it fall under the category of "immediate salam" if a university representative bought a thousand computers for one hundred thousand riyals, received only five devices, and the seller promised to deliver the rest the following day?

The aforementioned sale is valid and has the meaning of a forward sale (salam), but it does not fall under its technical definition. A salam is the delivery of an immediate counter-value for a deferred counter-value that is described in the liability. So, if what is permissible to be sold immediately via a salam is sold as a liability, it is valid, provided that the devices are known through sight or precise description.