desperately looking for a good LinuxCNC PC

Hello,
i've build many years ago a CNC. Then with a old P4 Lenovo Thinkcentre A52 or so. This was a realy bad choise with Jitter up to 200k. Then i've bought a Thinkcentre M57 because it has the same Size. This works better - with a jitter around 30k (i've thought... later i see 50k after 10h test). But then in the cold winter i started the system and it has many step loses. So i grab my scope and check what happend. The Pulses are to short (6µs instead 15µs) for my TB6500 Cards - wrong settings back then. Apparently this was a problem when it was cold. So i tried to set the Timing right but with the 15µs Pulewidth it gets very slow.
So then i tried evrything to get better jitter Values. Many configurations in the sparse bios - nothing helps. Then install a External Graphics. This helps - first. But after a while the jitter rises over the old values (70..80k).
After many tests i get mad and i see this:

So i search for a Dell Optiplex 960SFF and got one.
The test shows: Jitter arround 30k - so what should i do?
The Dell is not the same than the one in the wiki.
Here the Values:
Bios Version: A18 (current version)
Service Tag: 70N474J
Memory: 2GB, 800MHz, Single Channel, DDR2 - in DIMM3 Slot
Processor: Intel Core2 QUAD Q9550 @ 2,83GHz

I Disable the Diskette Drive, Use SATA in Legacy and tried a SSD. SMART is disabled.
Internal NIC and USB is enabled, Parallelport in PS2 Mode in Addr. 378h. Serial @ COM1.
Dissable the NIC does not effect the jitter.
Audio and Wifislot are dissabled.
Videocard onboard, a small ATI and 2 different NVIDIAs doesnt change much.
If i enable this: "enable multicore support" the jitter rises around 10k.
Speedstep and C States are dissabled. CPU Limit enable does not matter.
Virtualisation and VT is dissabled.

I've tried this images:
LinuxCNC 2.8.0 Debian 10 Buster PREEMPT-RT ISO
LinuxCNC 2.8.0 Debian 7 Wheezy RTAI
LinuxCNC 2.7.14 Debian 7 Wheezy

How do i test? I boot the system and then start latency-test and 5 times GLXGears.

So i dont know what to do....
Can you help me?

BR Raphael

Hello,
i run the pc over night. Now i see 2134451 ns Jitter in Servo Thread and 2209593ns in Base Thread. Thats worse...
I have some failures in my numbers - the driver is a TB6560 and the 15µs pulsewidth are 30µs and i can run up to 15kHz - what i need for my 1/16 microsteps.
www.mouser.com/datasheet/2/408/TB6560AHQ..._20141001-771503.pdf

So first thanks for your fast replies
the 15kHz is the maximum step pulse - 100kHz is the inner controlloop.
I want to drive with full 15kHz Steps for fast movement.

I Reconfigure with step conf.

Now i started with a Fresh Installation of www.linuxcnc.org/iso/linuxcnc-2.7.14-wheezy.iso on my SSD and this runs up to the values told in the last post. How can i dissable the sleepmodes?
i reboot and do the same test with the internal graphics. at the moment it is a: Nvidia G96 Geforce 9500GS

EDIT: The test runs now: 5times GLXGears with latencytest - it starts with 171689ns servo thread jitter and 26869ns Base Thread Jitter

Thanks for the hint. I asked Lascar.com for a price in germany.
So Stay tuned.
Which PC should i use for the CNCMill? The old fitting Lenovo Core2Duo or the "newer" Dell Core2Quad?
Should i upgrade the Memory? Lenovo: 1Gb and Dell: 2GB
BR

So, i upgraded the Memory and nothing changed. But then i add idle=poll to the grub kernel call and it changes drastical. i am down to 5000...7000 ns.
So i am happy now Thanks!