In IBM mainframe operating systems from the OS/360 and successors line, 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. Certain data within the UCB also instructs the Input/Output Supervisor (IOS) to use certain closed subroutines in addition to normal IOS processing for additional physical device control.
A similar concept in Unix-like systems is a kernel's devinfo structure, addressed by a combination of major and minor number through a device node.
Read more about Unit Control Block: Overview, Handling Parallel I/O Operations
Famous quotes containing the words unit, control and/or block:
“During the Suffragette revolt of 1913 I ... [urged] that what was needed was not the vote, but a constitutional amendment enacting that all representative bodies shall consist of women and men in equal numbers, whether elected or nominated or coopted or registered or picked up in the street like a coroner’s jury. In the case of elected bodies the only way of effecting this is by the Coupled Vote. The representative unit must not be a man or a woman but a man and a woman.”
—George Bernard Shaw (1856–1950)
“Magic is the envelopment and coercion of the objective world by the ego; it is a dynamic subjectivism. Religion is the coercion of the ego by gods and spirits who are objectively conceived beings in control of nature and man.”
—Richard Chase (b. 1914)
“Of course I lie to people. But I lie altruistically—for our mutual good. The lie is the basic building block of good manners. That may seem mildly shocking to a moralist—but then what isn’t?”
—Quentin Crisp (b. 1908)