To Grasp the Cloud—Fundamental Concepts - Deploying and Managing a Cloud Infrastructure - page 29

Even though the first generation of mainframe computers don't compare to today's cloud,
they do share the access and usage mechanism to some extent—hosted in dedicated
rooms (modern-day data centers) and served through terminals that can be connected to
them with multiple users (now scalable to hundreds of millions) who can deploy compute
jobs on them.
Contrary to popular belief, the modern generation of IBM mainframes are still very much
in use in a significant number of large organizations, running critical applications, storing
sensitive data, and executing many millions of transactions every single day. The scale
and penetration of IBM's mainframes was revealed in an antitrust investigation into IBM's
mainframe business line initiated by the EU Commission. You can find out more at
http://europa.eu/rapid/press-release_IP-10-1006_en.htm?locale=en
Elastic
This is a fundamental property that differentiates a cloud from any other “internetworked
collection of servers.” Elasticity enables cloud tenants to spin new virtual servers on demand
and on the fly. This way, compute resources can be seamlessly scaled up and down based on
demand. The fact that Amazon named its cloud product Elastic Compute Cloud (EC2) is a
perfect example of how important this property is.
Massive
Amazon has several data centers spread across multiple physical locations across the globe.
A single data center houses thousands and sometimes tens of thousands of physical servers
connected together through a high-speed network, and the data center is connected to a
high-speed Internet backbone. The scale at which public cloud providers operate is stagger-
ing; never before in the history of computing have we had these huge data centers accom-
modating tens of thousands of physical servers. Microsoft Azure and Google Cloud have
similar massive data centers, as do companies that do not sell computing resources but have
huge compute resource requirements for their own products. A perfect example would be
Facebook, which also has huge data centers spread across the world.
On Demand
The ability to set up and operate virtual servers ubiquitously and without the need to
provision any physical server resources is an intrinsic property of the cloud. A cloud ten-
ant can allocate networking, storage, bandwidth, and compute resources on demand
based on its own requirements or provisioning policies. All major public cloud vendors
have enabled High Availability (HA) and ubiquitous access, which enables tenants to spin