## MMPM/2 Device Driver Reference

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### Glossary - S

S

SBCS - Single-byte character set

SCB - See subsystem control block architecture.

screen device context - A logical description of a data destination that is a particular window on the screen. See also device context.

SCSI - Small Computer System Interface.

seamless windows - An architecture contained within OS/2 which permits one or more applications to share windowed desktop graphical space and other resources, while executing concurrently. Application session windows managed by seamless windows can share border information, and pointing device transitions from session to session are handled smoothly and transparently.

second-party DMA adapter - See DMA slave.

semaphore - (1) A variable that is used to enforce mutual exclusion. (T) (2) An indicator used to control access to a file; for example, in a multiuser application, a flag that prevents simultaneous access to a file. (3) An entity used to control access to system resources. Processes can be locked to a resource with semaphores if the processes follow certain programming conventions.

sense data - Data which describes an I/O error as defined by the ANSI SCSI specifications.

single-byte character set (SBCS) - A character set in which each character is represented by a one-byte code. Contrast with double-byte character set.

Small Computer System Interface (SCSI) - An input and output bus that provides a standard interface between the OS/2 multimedia system and peripheral devices.

spline curve - In computer graphics, a shape created when a user specifies a series of points and the computer software draws a curve that smoothly approaches those points.

spooler - A program that intercepts data going to a device driver and writes it to a disk. The data is later printed or plotted when the required device is available. A spooler prevents output from different sources from being intermixed.

synchronous - Pertaining to two or more processes that depend upon the occurrence of specific events such as common timing signals.