hyper-threading, multi-core, dual-core -- Hyper-Threading Technology and multi-core support


SCO OpenServer includes support for both Hyper-Threading (HT) Technology and the multi-core processor architecture.

Hyper-Threading Technology allows two series of instructions to run simultaneously and independently on a single Intel® HT-enabled processor. With Hyper-Threading Technology enabled, the system treats a physical processor as two ``logical'' processors. Each logical processor is allocated a thread on which to work, as well as a share of execution resources such as cache memories, execution units, and buses.

Hyper-Threading Technology can be used on an SCO OpenServer system that is equipped with an Intel Xeon(TM) or HT-enabled Intel Pentium® 4 processor and that also includes a chipset and a system BIOS with support for HT Technology.

A multi-core processor is a single physical processor that includes two or more ``cores'' and one or more logical processors per core. Each core acts as a discrete processor, complete with its own set of execution resources. A dual-core processor includes two cores, with one logical processor per core. A dual-core processor that also includes Hyper-Threading Technology provides two cores and two logical processors per core, allowing the execution of four simultaneous threads.

SCO OpenServer supports Intel Xeon and Intel Pentium 4 multi-core processors. SCO OpenServer's multi-core support also requires a chipset and a system BIOS that support HT Technology.

Note that most SCO OpenServer commands treat logical processors as physical CPUs. Depending on whether or not Hyper-Threading is enabled, the view that commands provide of your system will be different. For example:

Dual-processor system with Hyper-Threading disabled

# cpuonoff -c
CPU1: active
CPU2: active
# uname -X | grep NumCPU
NumCPU = 2

Dual-processor system with Hyper-Threading enabled

# cpuonoff -c
CPU1: active
CPU2: active
CPU3: active
CPU4: active
# uname -X | grep NumCPU
NumCPU = 4

When you use Hyper-Threading Technology with SCO OpenServer, you will most likely see system performance improvements. Depending on the workload applied to the system, however, it is possible you could see a decrease in performance. You will probably want to run some system benchmarks with Hyper-Threading enabled and disabled to determine which offers the optimal configuration for your system.


By default, support for Hyper-Threading is installed, but not enabled. To enable HT support:

  1. Add the following line to the file /etc/default/boot:

  2. Reboot the system to rebuild the kernel:
       shutdown -i6 -g0 -y

  3. As the system reboots, enter the system BIOS utility to enable hyperthreading in your system BIOS. (See the hardware manufacturer's documentation for details.) Save the BIOS configuration and reboot.

  4. After the system boots, use the psrinfo(ADM) command to check processor status.


SCO OpenServer does not distinguish between physical and logical processors. The SCO OpenServer base operating system license covers use of the physical boot processor and, by association, it's corresponding logical processors. For a single-CPU system, you can use Hyper-Threading without providing a license for additional CPUs. To take advantage of Hyper-Threading on auxiliary processors on a multi-processor system, you must purchase Additional CPU licenses. Each physical auxiliary processor requires a CPU license, and that license then supports all of the logical processors on the corresponding auxiliary processor.


This implementation of Hyper-Threading only works on a system that provides MPS tables in the BIOS. Newer Pentium 4 systems that only provide ACPI tables will not work with SCO OpenServer's Hyper-Threading implementation.


See also

boot(HW), cpu(HW), cpuonoff(ADM), mpstat(ADM)
© 2007 The SCO Group, Inc. All rights reserved.
SCO OpenServer Release 6.0.0 -- 05 June 2007