From BOL: Returns a miscellaneous set of useful information about the computer, and about the resources available to and consumed by SQL Server.

See Slava Oks's WebLog post on SQLOS's DMVs.

Note that the hyperthread_ratio value isn't very useful on multi-core processors. See the update to Umachandar's MSDN blog; Determining optimal MAXDOP setting from TSQL in SQL Server 2005.

SELECT
   si.cpu_ticks as cpu_ticks,
   (1.0 * si.ms_ticks / (24 * 60 * 60 * 1000)) as system_uptime_days,
   si.cpu_count as logical_cpu_count,
   si.cpu_ticks_in_ms as cpu_ticks_in_ms,
   si.hyperthread_ratio as hyperthread_ratio, -- not reliable.
   si.physical_memory_in_bytes / 1048576 as physical_memory_in_Mbytes,
   si.virtual_memory_in_bytes / 1048576  as virtual_memory_in_Mbytes,
   si.bpool_committed as bpool_committed_pages,
   si.bpool_commit_target as bpool_commit_target_pages,
   si.bpool_visible as bpool_visible_pages,
   (si.stack_size_in_bytes / 1024) as stack_size_in_Kbytes,
   si.os_quantum,
   si.os_error_mode,
   si.os_priority_class,
   si.max_workers_count,
   si.scheduler_count,
   si.scheduler_total_count,
   si.deadlock_monitor_serial_number
FROM
   sys.dm_os_sys_info si