IBM Systems Magazine, Mainframe - September/October 2012 - (Page 32)

Tech Corner Programming, systems operations and more From Small Beginnings The what and why of zEnterprise millicode By Bob Rogers M ost people in the mainframe community have heard the term millicode, but what is it? The short answer is it’s a form of microcode—one of the greatest ideas in computer engineering. Millicode embodies a very clever refinement of the basic idea. An important part of the mainframe’s history, microcode enables machines with differing internal designs and built on different hardware technologies to present a single architecture to software. Its introduction was a major contributor to the success of the IBM mainframe architecture in becoming the de facto standard for large-scale computers. Microcode made it all possible. First, let’s start by defining microcode, which is a layer of hardware-level instructions involved in the implementation of higher-level machine code instructions. This means microcode is a set of instructions in a simple architecture used to implement the instructions of a more complex architecture. Microcode was originally a simpler method of developing the control logic for a computer. Complex logic can be implemented with a sequence of simpler microcode instructions. Because it’s essentially a program, logic errors can be fixed with a reload without making any actual hardware changes. Microcode patches can be used to work around errors in the hardware during development or even in the field. A Very Brief History of Microcode IBM used microcode to create a full line of IBM System/360 processors in the mid-1960s, covering wide ranges of price and performance. They were built on different circuit technologies yet able to run the same programs. Prior to S/360, each computer was basically a Historical footnote The floppy disk was invented by IBM to provide a means to load microcode. Sometime around 1971, IBM started using 8-inch floppy disks as a medium for loading microcode into its System/370 computers prior to system IPL. 22 32 SEPTEMBER/OCTOBER 2012

Table of Contents for the Digital Edition of IBM Systems Magazine, Mainframe - September/October 2012

Table of Contents
Editor's Desk: Keep Your Eye on the Ball
IBM Perspective: Transforming Data Into Value
Focus on Storage: Smarter Solutions are Designed to Meet Increasing Demands for Information
Case Study: Bringing Order to Disorder: Commerce Bank employs an enterprisewide solution to track application changes
Cover Story: The Next Evolution in Hybrid Computing: IBM launches the second generation of zEnterprise-zEC12
Feature: Conquering Chaos: System z technology helps manage data mart complexities for business analytics
Feature: Split-Second Decisions: SPSS Modeler 15 offers real-time scoring for faster, more effective insights
Tech Corner: The What and Why of zEnterprise Millicode
Administrator: New DFSMS Features Increase the Availability of Data on System z
Solutions: CICS JS/Server V1.1 - DR/VFI- JCL-QA
Advertiser's Index
Stop Run: A 1440 Data Processing System Finds New Life After 50 Years
Reference Point - Global Events, Education, Resources for Mainframe
Women in Technology
Services Blueprint: A New Category of Computing - IBM PureSystems family
NEW 2013 Mainframe Buyer's Guide

IBM Systems Magazine, Mainframe - September/October 2012