mainframe usage: z/VM, z/VSE™, Linux for zSeries, and z/TPF.8 This text does not examine the marketing and pricing of mainframe software. However, the availability and pricing of middleware and other licensed programs is a critical factor affecting the growth and use of mainframes.
z/VM
z/Virtual Machine (z/VM) has two basic components: a control program (CP) and a single-user operating system, CMS. As a control program, z/VM is a hypervisor because it runs other operating systems in the virtual machines it creates. Any of the IBM mainframe operating systems such as z/OS, Linux for zSeries, z/VSE, and z/TPF can be run as guest systems in their own virtual machines, and z/VM can run any combination of guest systems. The control program artificially creates multiple virtual machines from the real hardware resources. To end users, it appears as if they have dedicated use of the shared real resources. The shared real resources include printers, disk storage devices, and the CPU. The control program ensures data and application security among the guest systems. The real hardware can be shared among the guests, or dedicated to a single guest for performance reasons. The system
programmer allocates the real devices among the guests. For most customers, the use of guest systems avoids the need for larger hardware configurations. z/VM’s other major component is the Conversational Monitor System or CMS. This component of z/VM runs in a virtual machine and provides both an interactive end user interface and the general z/VM application programming interface.
z/VSE
z/Virtual Storage Extended (z/VSE) is popular with users of smaller mainframe computers. Some of these customers eventually migrate to z/OS when they grow beyond the capabilities of z/VSE. Compared to z/OS, the z/VSE operating system provides a smaller, less complex
base for batch processing and transaction processing. The design and management structure of z/VSE is excellent for running routine production workloads consisting of multiple batch jobs (running in parallel) and extensive, traditional transaction processing. In practice, most z/VSE users also have the z/VM operating system and use this as a general terminal interface for z/VSE application development and system management. z/VSE was originally known as Disk Operating System (DOS), and was the first disk-based operating system introduced for the System/360 mainframe computers. DOS was seen as a temporary measure until OS/360 would be ready. However, some mainframe customers liked its simplicity (and small size) and decided to remain with it after OS/360 became available. DOS became known as DOS/VS (when it started using virtual storage), then VSE/SP and later VSE/ESA™, and most recently z/VSE. The name VSE is often used collectively to refer to any of the more recent versions.
Linux for zSeries
Several (non-IBM) Linux distributions can be used on a mainframe. There are two generic names for these distributions:
_ Linux for S/390 (uses 31-bit addressing and 32-bit registers)
_ Linux for zSeries (uses 64-bit addressing and registers)
The phrase Linux on zSeries is used to refer to Linux running on an S/390 or zSeries system, when there is no specific need to refer explicitly to either the 31-bit version or the 64-bit version. We assume students are generally familiar with Linux and therefore we mention only those characteristics that are relevant for mainframe usage. These include the following: Linux uses traditional count key data (CKD 9disk devices and SAN-connected SCSI-type devices. Other mainframe operating systems can recognize these drives as Linux drives, but cannot use the data formats on the drives. That is, there is no sharing of data between Linux and other mainframe operating systems.
___ Linux does not use 3270 display terminals, while all other mainframe
operating systems use 3270s as their basic terminal architecture.10 Linux uses X Window System based terminals or X-Window System emulators on PCs; it also supports typical ASCII terminals, usually connected through the telnet protocol. The X-Window System is the standard for graphical interfaces in Linux. It is the middle layer between the hardware and the window
manager.
____With the proper setup, a Linux system under z/VM can be quickly cloned to make another, separate Linux image. The z/VM emulated LAN can be used to connect multiple Linux images and to provide an external LAN route for them. Read-only file systems, such as a typical /usr file system, can be shared by Linux images.
___ Linux on a mainframe operates with the ASCII character set, not the EBCDIC11 form of stored data that is typically used on mainframes. Here, EBCDIC is used only when writing to such character-sensitive devices as
displays and printers. The Linux drivers for these devices handle the character translation.
z/TPF
The z/Transaction Processing Facility (z/TPF) operating system is a special-purpose system that is used by companies with very high transaction volume, such as credit card companies and airline reservation systems. z/TPF was once known as Airline Control Program (ACP). It is still used by airlines and has been extended for other very large systems with high-speed, high-volume transaction processing requirements. z/TPF can use multiple mainframes in a loosely-coupled environment to routinely handle tens of thousands of transactions per second, while experiencing uninterrupted availability that is measured in years. Very large terminal networks, including special-protocol networks used by portions of the reservation industry,
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