Specifications

Glossary

Glossary-11

thread

An abstraction of the concept of execution in a shared address space. A sequence of

instructions that are executed as an independent entity and are scheduled by system soft-

ware.

unbuffered I/O

I/O that bypasses the file system cache for the purpose of increasing I/O performance for

some applications.

upstream

The direction of STREAMS messages ﬂowing through a read queue from the driver to the

user process.

user space

The part of the operating system where programs that do not have direct access to the ker-

nel structures and services execute. The UNIX operating system is divided into two major

areas: the user programs and the kernel. Drivers execute in the kernel, and the user pro-

grams that interact with drivers execute in the user program area. This space is also

referred to as user data area.

volume table of contents (VTOC)

Lists the beginning and ending points of the disk partitions speciﬁed by the system admin-

istrator for a given disk.

write queue

The half of a STREAMS module or driver that passes messages downstream.