Today in 1964, the International Business Machines Corporation, more commonly known as IBM, announced its System 360 line of computers. The System 360 represented a milestone in computer history that helped IBM to become the largest computer company in the world. The “360” in the name indicated the 360 degrees of a circle, meaning that the System 360 was designed to be a single computer family for all types of computer work. In the 1960s, this mainly meant doing both business administration-type tasks and computation-intensive engineering tasks. Previously, computers had been designed to do one or the other pretty much to the exclusion of anything else.
For those unfamiliar with the computers of the 1960s, it is worth pointing out how the System 360 machines looked. They were large refrigerator-like boxes, located in special computer centers with air conditioning and powerful power supplies, and tended to by specialists in white coats. A single computer could occupy several cabinets, and have many tape drives, disk drives, printers, and punched card readers attached.
Most importantly, the System 360 was not a single computer, but rather a whole range of computers with different price points and performance levels. Initially, IBM announced six different models and, over the coming years, many more were introduced. These computers would all run the same software programs, and let customers upgrade to bigger machines as their businesses grew. In today’s computer market, this is something we take for granted. For example, we can buy a 300 dollar netbook which essentially can run the same software as a 30000 dollar server, albeit slower. In 1964, this similarity was considered revolutionary. Many people within IBM doubted that it could be done at all. But it was done, and at its launch, the fastest System 360 machine was about 25 times faster than the slowest. In 1970, the System 360 models offered by IBM spanned a performance factor of 200.
The key to the System 360 design was the idea of using common instruction set architecture across a range of computers. For those less familiar with how computers work, the instruction set of a computer determines which programs it can run. Programs written to use one instruction set cannot run on a computer using a different instruction set. For example, programs for Apple’s iPhone do not work directly on Apple desktop machines, as they use different instruction sets.
Prior to the System 360, there had been ad-hoc efforts at making new computer systems run the same software as older computer systems. The System 360 made this an explicit promise, and machines were marketed as part of the family with a guarantee that existing software would work on the new machines.
Looking back at this decision from 2010, it can be seen to signify a maturing of the information technology field. Today, the common wisdom in the computer industry is that software is more important than hardware. People and businesses buy computers to run certain software on them, and the hardware is of secondary importance. We make the choice between Windows, Linux, or MacOS when buying a new computer. In the early days of the computer, the hardware was primary and the software was created after the hardware, and it was normal to rewrite all software when a new computer was acquired. As business usage of computers increased, more and more effort was invested in software, and the value of the software began to overtake the value of the computers on which it was run.
The System 360 proved very popular with customers and IBM's sales doubled from 1965 to 1970. In the mid-70s, IBM as a company was as big as the rest of the US computer industry combined. The success of the System 360 drove other firms to create compatible machines, creating for the first time a computer market in which different vendors sold machines that would compete on performance and price, but run the same software.
The System 360 was also copied by the Soviet Union and Eastern Bloc nations. In the 1970s, the Soviet Union decided to clone the System 360 architecture instead of using a homegrown design. The machines were called “ES EVM”, and more than 15000 were manufactured up until 1998. Thus, the IBM System 360 ended running the most important business computer systems on both sides of the iron curtain. When the Cold War ended, this turned out to be a blessing for IBM, as the old East provided a large pool of programmers skilled in the System 360 architecture, while Western computer science students had long moved on to newer technology like PCs and client-server computing.
Over the years, the architecture of the System 360 has been upgraded and developed. The first major upgrade was the System 370 announced in 1970, and in 1990, another redesign gave it the new name System 390. In 2000, the name was changed to “zSeries” following another major redesign to extend the amount of memory the computers could use. The “z” indicates “zero downtime”, the main selling point of mainframe computers today. The most recent generation of the System 360 lineage is the the “z10”. The z10 can essentially still run all the software written since 1964, as well as newer software which can take advantage of the new features of the System 370, System390, and zSeries. To an outsider, it can be quite surprising to realize just how much decades-old software is still in active use in many businesses, for the simple reason that there is no point in fixing what is not broken.
IBM “mainframe” computers, offered referred to as 'big iron' by IT workers, still run many of the most critical computer functions of our modern society, in particular in the financial system. The IBM mainframes have a reputation for outstanding stability and reliability, as well as services and support that -- while costly -- ensure that the computers never go down and that business never stops. IBM’s mainframe computers are not the dominant force in the computer industry that they once were, but they are still a major business, even if it is far out of the public eye. It is quite possible that the descendants of the System 360 will continue to be around for many decades to come. So far, all predictions about the death of the mainframe have proven to be false.