Mainframe architectures are fundamentally designed for high-volume, I/O-intensive workloads, such as online transaction processing and batch processing. Consequently, the performance of the I/O subsystem is a critical factor and a common source of bottlenecks. Slow performance of storage devices, historically Direct Access Storage Devices (DASD), directly impacts the system's ability to meet its processing objectives. I/O response time is a key metric in mainframe performance analysis, making slow storage speed a typical and significant performance risk inherent to this architecture.

A. Inconsistent loads when accessed via APIs: This is a workload-related risk that can affect any type of server architecture, not one that is uniquely typical for mainframes.

C. Misconfigured host machine: Misconfiguration is a universal operational risk applicable to any computing platform and is not a risk specific to mainframe architecture itself.

D. Lack of RAM: Insufficient memory is a generic resource constraint that degrades performance on any computer system, not a risk characteristic of mainframes in particular.

1. IBM Redbooks. ABCs of z/OS System Programming Volume 2

SG24-6982-00. Chapter 5

"I/O processing in z/OS

" details the critical nature of the I/O subsystem

including DASD

and its direct impact on system performance. It states

"The I/O subsystem is a major component of a z/OS system. Its performance is critical to the overall performance of the system." (Page 137). [Direct URL: https://www.redbooks.ibm.com/redbooks/pdfs/sg246982.pdf]

2. Živkovič

A.

& Šumak

B. (2011). Performance Analysis of Mainframe Computer Systems. International Journal of Electrical and Computer Engineering Systems

2(2)

61-68. This academic paper discusses mainframe performance

noting that "The I/O subsystem is one of the most complex parts of the mainframe computer system... The most important performance measures for DASD devices are response time

I/O rate

device utilization..." (Section 3.2

p. 64). [Direct URL: https://hrcak.srce.hr/file/116185]

3. University of Arkansas

Walton College of Business. ISYS 5503: Mainframe Computing

Course Notes. Course materials frequently emphasize the I/O-centric nature of mainframes and the importance of storage (DASD) performance tuning as a core discipline in mainframe systems management.