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The System/34 could either swap out entire programs, or individual segments of a program in order to free up memory for other programs to run. One of the machine's most distinctive features was an off-line storage mechanism that utilized " magazines "—boxes of 8-inch floppies that the machine could load and eject in a nonsequential fashion.
Channels have their own instruction set, and access memory independently of the program running on the CPU. On the smaller models (through 360/50) a single microcode engine runs both the CPU program and the channel program. On the larger models the channels are in separate cabinets and have their own interfaces to memory.
Virtual Storage Access Method (VSAM) [1] is an IBM direct-access storage device (DASD) file storage access method, first used in the OS/VS1, OS/VS2 Release 1 (SVS) and Release 2 (MVS) operating systems, later used throughout the Multiple Virtual Storage (MVS) architecture and now in z/OS.
Traditionally IBM Mainframe memory has been byte-addressable. This kind of memory is termed "Central Storage". IBM Mainframe processors through much of the 1980s and 1990s supported another kind of memory: Expanded Storage. It was first introduced with the IBM 3090 high-end mainframe series in 1985. [28] Expanded Storage is 4KB-page addressable.
Block diagram of count key data track format used on IBM mainframe computers beginning with S/360 shipment in 1965. The reason for CKD track format is to allow data field lengths to vary, each recorded block of data on a DASD track, called a record has an associated count field which identifies the record and indicates the size of the key, if used (user-defined up to 255 bytes), and the size ...
File status okay; about to open data connection. 200 Series: The requested action has been successfully completed. 202: Command not implemented, superfluous at this site. 211: System status, or system help reply. 212: Directory status. 213: File status. 214: Help message. Explains how to use the server or the meaning of a particular non ...
Later-model PDP-11 processors include memory management to support virtual addressing. The physical address space was extended to 18 or 22 bits, hence allowing up to 256 KB or 4 MB of RAM. The logical address space (that is, the address space available at any moment without changing the memory mapping table) remains limited to 16 bits.
In IBM mainframe operating systems OS/360 and its successors, a Unit Control Block (UCB) is a memory structure, or a control block, that describes any single input/output peripheral device (unit), or an exposure (alias), to the operating system.