
28 Cray T3E User’s Guide
3.8 The UNICOS/mk operating system
The Cray T3E has a distributed microkernel based operating system.
This provides a single system image of the global system to the user.
UNICOS/mk is a Unix-like operating system based on Cray’s UNICOS
system, which runs on parallel vector processor (PVP) platforms such as
the Cray C90.
The microkernel is based on the CHORUS technology. It provides ba-
sic hardware abstraction, memory management, thread scheduling and
interprocessor communication between the processes.
Several processors offer operating system (OS) services, “servers”. These
servers look like normal processes running on top of the microkernel.
The most important OS servers are listed in Table 3.2. Additionally,
various servers manage logging, devices, and other operating system
services.
Server Function
Process Manager (PM) Manages processes local to its PE
Global Process Manager (GPM) Manages list of all known processes
Global Resource Manager (GRM) Tracks and allocates the resource
management
Configuration Server (CS) Processes requests for system
configuration data
File Server Provides file system services
File Server Assistant Provides file system services locally
Table 3.2: Some UNICOS/mk high-level OS servers.
The user communicates with the servers using normal Unix-type appli-
cation programming interfaces (APIs) like in any other Unix system, i.e.,
using libraries and system calls.
Scalability is an important issue in a system like the Cray T3E. When the
system size is increased, not only the number of application processors
is affected, but also the number of command and OS processors. The
command processors run interactive user jobs and the operating system
processors run OS servers.
3.9 File systems
The Cray T3E running UNICOS/mk has a similar file system structure
as many other Unix systems. These include the file systems / (root
directory), /usr/ and /tmp/.
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