Exophase said:
People like to assume that non-Windows is automatically better no matter what, which I find rather strange. Especially since ever since I moved to Linux (Ubuntu) I've had performance problems left and right that I never had on Windows XP. It doesn't take a lot for Firefox or even Pidgin to start chugging, gvim starts hiccuping if I have multiple tabs open, in general more than 20-30% CPU is being used.. and this is with a 1.8GHz Core 2, not some old CPU. It's actually a better system (better CPU, more RAM) than I was using in Windows.
Ubuntu just loves paging stuff out to disk, even when you have piles of memory available.
If I'm watching a movie, and pause it to go to the washroom, when I get back it takes several seconds(and a bunch of HDD activity) to begin playing again. I had to RMA my Seagate drive a little while ago, and during that time I was running off an old 8GB PATA Fujitsu - with that drive, unpausing a movie took about a dozen seconds.

There was also visible lag when moving windows around, and exiting black-desktop (What do you call it when the desktop goes a fake black rather than turning the monitor off?) would lag for several seconds as well.
Many people praise Vista/Win7 for using memory as a cache. Apparently Linux does the same (sort of) - but I haven't seen it.

I much prefer XP's method - use as little memory as possible, so that programs that need more will be able to use that memory, and run faster.
I've often thought the only solution to this is to have a way to signal programs to use less memory. I was reading an article about the new DiskDefrag for Win7, which uses ~90% of your free memory to slightly speed up defragging. Some of us have multiple HDDs and actually use our computers during defrag, so when paired with a web browser, it'll quickly be paging memory to disk, and grinding performance downward. If there were a way for the kernel to signal the program to flip to low-memory mode, it could drop from 3.3GB (or whatever) back to the old 60MB, giving you plenty of memory for all your running stuff.
Shockingly, nobody has implemented this in any OS, to my knowledge? I've been wondering about this for about a decade!
Edit: ReactOS is pretty impressive, but I suspect the XP kernel is faster. XP is padded with bloat, but if you trim it down, it really is quite speedy. Modding a few system files and cutting away bloat with nLite can leave it remarkably lean. My base XP install is just over 400MB, but has full java/.net/game/free-software support. Runs just about everything except Microsoft programs.
By cutting away extra drivers and tuning it for your specific box, it becomes remarkably optimized. At boot I have about 14 processes running, consuming almost 50MB of memory. After steam and some other stuff starts up, it's running over 100 threads and almost 1.5k handles. Check the task manager(Performance tab) to compare.
After trimming it down, I noticed a ~15% speedup in benchmarks. (though to be honest, I used to be CPU limited - now I have a newer CPU) I also noticed that the behaviour of slowing down over time completely vanished. I can have it encoding videos for days, and as soon as it's done, and I close the program, it's right back to the speed of a fresh boot. I find it really amusing with games like Left4Dead, which I can alt-tab out of and back into in about 2 seconds. Apparently it's much higher for most people.
So my opinion is ReactOS has a long way to go before it can claim to be faster than the XP kernel - but it certainly is free-er.

I'll reserve my judgements until it matures a bit more. However, I've learned off Ubuntu(and XP) that a fast kernel can translate into a slow OS if all the programs running on it are coded poorly or were coded in fully interpreted languages. Too much bloat/overhead will drag even the best kernel down.
Edit2: Tried my modded XP on a P2 233mhz laptop with 128MB of RAM and one of those old slow (4500RPM?) PATA drives. It boots in 20 seconds, opens Firefox in 8, and OpenOffice in about 14.