Feature for feature, the mainframe ate the personal computer’s lunch. The IBM System/370 Extended Architecture Mainframe released in 1983 was a 31-bit machine that could support up to 8MB of memory with a processor running at 38 MHz. By comparison, the IBM PC-XT, also released in 1983, was an 8-bit machine that shipped with 128KB of RAM and an 8088 processor that ran at a speed of 4.77 MHz.
But, as the saying goes, “You should never underestimate the value of cool,” and the PC was very cool. It got a lot of attention while the mainframe stayed hidden away in climate-controlled rooms in the basements of banks and insurance companies. Yet, the mainframe was more powerful, and whereas the PC was meant to meet the needs of a single user, a mainframe can service thousands.
Built to Scale Built from Inception
Mainframe computers from the start were designed to support hundreds (if not thousands) of users. However, more importantly, mainframes were and are designed to support millions of concurrent transactions. When you think about it, while it’s possible for a high number of user requests to exhaust CPU utilization in a typical commodity machine—which is the reasoning for being able to scale up CPU count by increasing VM allocation in the cloud-based computing cluster—the real burden on the CPU is not so much the request count but the computing burden that each request incurs. For example, one request getting a .JPG of a cat will incur nowhere as much burden as a request that needs to convert an audio file in .WAV format to MP3.
The need to alleviate request burden has been around since bank tellers working in the various branches of a big bank had to make deposits and withdrawals at the same time. Mainframe engineers addressed the problem decades ago. Technologies such as batch processing and message queues, which make computational activity asynchronous and are optimized to fully utilize CPU capacity efficiently, were and are commonplace in the mainframe landscape.
IBM’s 360 mainframes supported batch processing in its OS/360 system starting in 1964. Batch processing allows thousands of instructions to be performed on terabytes of data at pre-scheduled times (usually “off-hours”), all without human intervention.
Message queuing allows processes to take data in the form of a message stored in a message queue and perform computational activity according to the data in the message. Processing is performed independent of a request in an asynchronous manner. When processing is complete, a new message is created and sent on to another queue, where another process will do more processing or create a notification indicating that work is complete. IBM MQSeries was an early message-queuing technology first used in 1993 at State Street Bank well before the internet became commonplace.
The reason that support for user and transactional concurrency was possible in mainframes is due to a technology that is commonplace in today’s cloud environment but was unheard of among PC users back in the days when most data was exchanged between standalone PCs using floppy disks. That technology is virtualization.
Virtualization Takes Mainframe Computing to the Next Level
Today we take virtualization—the capability to have software simulate hardware—for granted. Without it, we couldn’t have native cloud providers such as Amazon Web Services, Google Cloud and Microsoft Azure. These services rely on virtualization to provide the segmentation and computational isolation required to meet the needs of the modern computing. Yet, as essential as virtualization is in the world of commodity cloud computing, putting a layer of virtual machines on a commodity PC is a fairly recent event in the history of computing. VMWare, VirtualBox and KVM became mainstream in the mid-2000s. On the other hand, virtualization has been part of mainframe technologies since the mid-1960s. Virtual memory appeared in the mainframe in 1965. Machine virtualization was introduced on the IBM 370 mainframe in 1972 and is still an important part of the mainframe computing experience today.