Operating System Overview
The OS Overview window gives a quick access to the activity of a Windows target.
CPU (% time)
Idle Percentage of time the processor is idle. User Percentage of elapsed time the processor spends in the user mode. User mode is a restricted processing mode designed for applications, environment subsystems, and integral subsystems. The alternative, privileged mode, is designed for operating system components and allows direct access to hardware and all memory. The operating system switches application threads to privileged mode to access operating system services. Privileged Percentage of elapsed time that the process threads spent executing code in privileged mode. When a Windows system service in called, the service will often run in privileged mode to gain access to system-private data. Such data is protected from access by threads executing in user mode. Calls to the system can be explicit or implicit, such as page faults or interrupts. Unlike some early operating systems, Windows uses process boundaries for subsystem protection in addition to the traditional protection of user and privileged modes. Some work done by Windows on behalf of the application might appear in other subsystem processes in addition to the privileged time in the process.
Cache Cache is the sum of the following counters:
System Cache Resident Size of the pageable operating system code in the file system cache. This value includes only current physical pages and does not include any virtual memory pages not currently resident. It does equal the System Cache value shown in Task Manager. As a result, this value may be smaller than the actual amount of virtual memory in use by the file system cache. System Driver Resident Size of the pageable physical memory being used by device drivers. It is the working set (physical memory area) of the drivers. System Code Resident Size of the operating system code currently in physical memory that can be written to disk when not in use. Pool Paged Resident Size of the paged pool. The paged pool is an area of system memory (physical memory used by the operating system) for objects that can be written to disk when they are not being used. Space used by the paged and nonpaged pools are taken from physical memory, so a pool that is too large denies memory space to processes.
Commited Amount of committed virtual memory. Committed memory is the physical memory which has space reserved on the disk paging file(s). There can be one or more paging files on each physical drive.
Run-Q Number of threads in the processor queue. Unlike the disk counters, this counter shows ready threads only, not threads that are running. There is a single queue for processor time even on computers with multiple processors. Proc. Number of processes in the computer at the time of data collection.
Page Activity (/sec)
In Rate at which pages are read from disk to resolve hard page faults. Hard page faults occur when a process refers to a page in virtual memory that is not in its working set or elsewhere in physical memory, and must be retrieved from disk. When a page is faulted, the system tries to read multiple contiguous pages into memory to maximize the benefit of the read operation. Out Rate at which pages are written to disk to free up space in physical memory. Pages are written back to disk only if they are changed in physical memory, so they are likely to hold data, not code. A high rate of pages output might indicate a memory shortage. Windows writes more pages back to disk to free up space when physical memory is in short supply. Faults Average number of pages faulted per second. It is measured in number of pages faulted per second because only one page is faulted in each fault operation, hence this is also equal to the number of page fault operations. This counter includes both hard faults (those that require disk access) and soft faults (where the faulted page is found elsewhere in physical memory.) Most processors can handle large numbers of soft faults without significant consequence. However, hard faults, which require disk access, can cause significant delays.
% Rd time Percentage of elapsed time that the disk drives were busy servicing read requests. % Wr time Percentage of elapsed time that disk drives were busy servicing write requests. Queue Length Number of requests outstanding on the disk at the time the performance data is collected. It also includes requests in service at the time of the collection.Multi-spindle disk devices can have multiple requests that are active at one time, but other concurrent requests are awaiting service. This counter might reflect a transitory high or low queue length, but if there is a sustained load on the disk drive, it is likely that this will be consistently high. Requests experience delays proportional to the length of this queue minus the number of spindles on the disks. For good performance, this difference should average less than two.
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