First of all, my experiences of OS X are;
1. OS X 10.4.x - installed on my iBook G4 which was purchased April 2005. I installed many applications, including trying a lot of shareware from Apple.com downloads as I was a new Mac user. I also ported a large amount of my music and photo collections across. As time progressed, I eventually only had 3 gigs of disk space free. My system was still as quick as the first day I booted it.
2. OS X 10.5.x - installed on my Macbook Pro, purchased mid-June 2009. I ininitally powered up and played with the system before porting across all of the applications and data I had on 10.4.x. Now, if filling up the disk or installing applications were to slow down the system, I would have noticed it. But the system is still super quick (and hopefully quicker again once my Snow Leopard disk arrives).
Secondly, the reason for slow down on PC's is due to a range of issues;
1. The registry: By far the weakest park of Windows, but not something MS can easily remove as it is the long established mechanism for maintaining applications and services. When programs are removed, especially if not done via the correct process, will leave a load of junk in here. Parsing the registery tree takes longer and longer, and as more processes are run (often in the background during startup), the more often parsing is required.
2. Virus / Malware protection. Due to the higher number of threats for a windows system, any protection needs to be more detailed and thorough. This means more active processes, more CPU cycles and memory used to run virus / malware protection, etc, etc.
3. Fragmentation: Windows systems seem to slow down significantly if the drive becomes fragmented. Not something I've noticed (or worry about) on OS X.
4. Page files: The way windows implements memory page files is a lot less intelligent than OS X and many other systems. I'm not sure if this has been addressed in Windows 7, but the key weakness is that key parameters of how the pagefile works is set upon initial installation and not re-optimised when the system has had many more applications installed.
5. Poor application management: A lot of applications will install self-loading applets that load in system tray (or in the background), generally to make running their applications quicker or to detect events that their applications need to know (such as connection of a device). It is not uncommon for these to remain, even after the application has been un-installed. The more of these background processes that load, the slower the system becomes.
6. DLL Madness. There is a mix of control mechanisms over the installation and management of DLLs, which can mean that one application will override the DLLs of another. This can slow applications calling these libraries. Again, DLLs are a legacy of previous windows versions and it will be difficult for MS to resolve this.
Well, these are my opinions gained from many years of using both systems. The only version of Windows I actually thought was good, was the original version of NT. This was true 'New Technology' as badged by MS, but it was clear by later versions that MS was on the path to merge it's consumer OS with the Business orientated NT, and started to introduce traditional windows mechanisms which made NT less attractive.
Phil
