grows, complexity is added, and thus the risk of security breaches and the risk of duplicating data increases. Scalability and workload management requirements As organizations grow, the demands on their transaction processing environment also increases. Scalability is the ability to scale the system to meet these increased demands. Mainframe systems can readily scale vertically (within the machine) and horizontally (across machines). Distributed transaction processing systems can traditionally scale vertically with few problems. However, they frequently lack similar horizontal scaling capabilities to dispatch transactional requests from clients, with affinity between two or more machines. With increased scalability comes increased workload management requirements. Mainframe systems are capable of effectively managing complex and high-volume workloads of hundreds of millions of transactions per day. While processor speeds of distributed systems can execute instructions very fast within the same machine, comparable workload management facilities from distributed solutions are either present, but at a lower level of functionality, or not available at all. To achieve a similar level of functionality to a mainframe system requires several distributed systems coupled together to give the appearance of a harmonized environment. This increases not only the complexity but also the cost of people to manage the environment and the likelihood of networking outages. Distributed environments excel where the requirement for administration and workload management is lower. Core and supplementary functional requirements Both the mainframe and distributed platforms offer a choice of transaction processing monitors that deliver the core managed transactional attributes of atomicity, consistency, isolation, and durability. More advanced capabilities depend upon the maturity and quality of the software combined with the capabilities of the underlying hardware and operating environment. 1.10.2 Technical considerations The following sections provide a number of comparisons between mainframe and DTP systems from a technical perspective. Administrative and workload management requirements Mainframe systems are capable of effectively managing complex and high volume workloads. Comparable facilities from distributed solutions are now exhibiting similar behaviors, but often present a lower level of functionality. Chapter 1. Introduction to IBM distributed CICS products 31