Why do programs need special support to use 2 processors?

[ShawnD1]

Why is it that games are unable to use 2 or 4 processors? Aren't processes and threads controlled by the OS, not the program itself?

[bailey]

dual cpu's are normally used in servers, they can use up to 32 cpu's
normal home computers normally use one, and so that is the way the programs are written,
the closest thing you can do is to use hyperthreading and that will givy your system the effect of two cpu's
but the programs still need to be written to take advantage of it

[ShawnD1]

I'm wondering because I've seen a video for BeOS (old school) where the demo computer was a dual P2. In all applications the guy used (video, audio, presentaton software), both processors were being used.

Is MS Windows dropping the ball and just leaving it up to the program itself to handle the hardware? DOS was notoriously bad for that. That's why programs for DOS and Windows 95 (still a DOS based OS) always required users to manually input IRQ values for sound, and where the printer is, and what serial port to use. Could it be that programs still need to be specially made to use several processors even though that is the job of the OS?

[adam-red]

With an application ran on a dual processor machine, the CPU usage isn't less, but the workload is divided between the two processors. This speeds things up a bit, but not because the software was specifically designed to do so. 3DS Max on the other hand is coded to divide tasks between the two processors, but in a manner which takes the most advantage of the machine.
This is multithreading.

http://www.cswl.com/whiteppr/white/multithreading.html

[SpookyEddy]

Many applications are written with a single CPU bound process, as a result having more than one CPU is not an advantage (can be quite the oposite as running multiple CPU's has some overhead). If you coded a game that shared the workload across several threads then these could be farmed off onto seperate CPU's (the OS would take care of this), however the increased complexity and overhead of having to deal with synchronisation issues etc currently makes this an unpopular choice (also not worth it as relatively few home users have dual CPU boxes).

Regards

ed