According to Dell, the commitment is an expansion of the current relationship between the two companies, and will have Salesforce utilizing Dell's Isilon scale-out NAS storage arrays, data protection products and PowerEdge servers. Dell also announced that Salesforce plans to equip its 25,000 employees with Dell Latitude laptops.
As for the infrastructure plans, it's unclear how the datacenter commitment relates to Salesforce's use of Amazon Web Services and cloud-based infrastructure.
A year ago, Salesforce announced that it would use AWS to host its core services as part of a major international infrastructure expansion, and many of Salesforce's services run on AWS today, including Heroku, SalesforceIQ and Salesforce IoT Cloud. Presumably, Salesforce will continue to use the public cloud in combination with its own data centers, although it's likely the company will rely less heavily on data centers in the future.
In a canned statement, Salesforce CEO Marc Benioff said he is "thrilled" to extend the company's relationship with Dell Technologies and that Salesforce aims to "deliver the scale and innovation to support the needs of Salesforce's growing global customer base."