Athlon 750 at 127MHz FSB (254DDR), 1/3 L2 cache ratio
Overclocking
Abit actually give you 3 different ways to overclock on this motherboard..
FSB-based Overclocking
Abit's inclusion of SoftMenuIII on this motherboard is a welcome
sight for Athlon tweakers. In this incarnation it allows a wide
range of FSB/PCI speeds, from 100/33MHz right up to 155/38MHz,
22 settings in total with no annoyingly large jumps (the largest
being 5Mhz at the top end, it goes 140, 145, 150, 155). However,
we've seen these unrealistically high FSB settings on Athlon boards
before - there's no point having them in the BIOS if all you get
for selecting them is a blank screen. The highest I've seen actually
work is 115MHz on the Epox EP-7KXA (reviewed here). As usual, I slowed the memory timing
way down to make sure that wasn't the limiting factor, turned
off UDMA on the HDD's to avoid any possible corruption at high
PCI speeds, set the L2 cache ratio to 1/3 and had a play with
the FSB settings. The result? 124MHz is rock-stable (could happily
run Q3 timedemos and 3DMark2000, 127MHz starts to flake out a
bit (Sandra OK, locks up in 3D games, occasional blank screen
when warm-booting - hitting the reset button lets it restart fine),
133/44 is blank screen as is 136/34.
After my K7V review (here), I received a couple of emails from people saying they had more success at getting higher FSB's using the jumper block onboard, rather than the BIOS settings. One reader even claimed to have the board stable at 133MHz! Now, I couldn't replicate their success at all with that board, not being able to hit higher than the 107MHz FSB I'd gotten with the BIOS. Still, I figured it was worth a try on the KA7 as it has a similar jumper block. Sadly, there was no difference. The jumpers allow a setting of 133/33, but that just gave me a blank screen again.
"CPU FSB Plus (MHz)" Overclocking
This second method of overclocking is unique to the KA7. As well
as the usual FSB setting in the BIOS, there's also a "CPU
FSB Plus (MHz)" option, which lets you raise the FSB by a
few additional MHz (up to 28, which is 56 DDR) without raising
the memory, PCI or AGP speeds. Neato! As I'd already established
that 124MHz FSB was the limit of stability for me, I tried to
add a single MHz. It would boot ok, but lock up in q3 timedemos.
However, if I left the system at 100/33 (default), I could add
24MHz with this option, and everything was still fine. So my Athlon
750 was running at 933MHz core speed, FSB was 248MHz DDR, but
my memory was still at 133MHz, my PCI was a stock 33MHz and AGP
was a stock 66MHz. Trying to add 25MHz gave me similar errors
to when I tried to set a normal 127MHz FSB, or add 1 to the 124MHz
FSB.. obviously, I'm hitting a pretty hard limit at 124MHz. This
is still pretty cool though, if you have a PCI or AGP device that
will only cope with a certain speed, you can set the PCI to that
and raise the FSB to the motherboard/cpu limit.
Swapping to an Athlon 550 (not sure of the core, it's on loan so I can't rip it open :) ) had exactly the same results. Trying some different RAM and video cards didn't change it either, so it seems to be a motherboard limit.
Boosting the I/O and SDRAM voltage, which the KA7 allows in the BIOS, had no effect. In fact, I've never seen it have an effect in any situation on any motherboard. I guess I've never been quite on the knife-edge of stability enough.
GFD-based Overclocking
Ok, nothing new here. Crack the cpu case open, wave goodbye to
your warranty, stick a GFD onto your Athlon, set your desired
voltage and multiplier and away you go. I got my 950-cored 750
up to 1GHz pretty easily with the Outsideloop Afterburner and
the Hypascend Paradox. There seems to be some compatability issue
with the Northwind GFD 2.0, though, as all I could get with that
was a blank screen. For a full comparo of these GFD's (and a few
others) check here.
You can combine these three methods, as they all do different things. Use a GFD to set your multiplier, bump the FSB a little and change the L2 ratio with the BIOS, no problems. The only clash is voltage selection - normally, the BIOS setting will override what you set on the GFD. If the BIOS is set to "CPU Default", then the GFD's setting is used. The BIOS will let you set .2v higher than the chip's default, normally 1.6v so a maximum of 1.8v. However, if you set the GFD to, say, 1.7v, the BIOS changes to a maximum of 1.9v. I'm not sure what the upper limit is and I'm not game to find out.
With some experimentation I discovered the limit of my core is about 1050MHz at 1.8v. My CPU is water-cooled, so it's pretty comfortable at that voltage. I knew the machine was stable at 124MHz, so to get the best of both worlds I chose a multiplier of 8.5. This gives me a nice high core speed, but also the advantage of high PCI/AGP and memory overclocking. The next step, 124x9 for a core speed of 1116MHz, would die just before getting to the desktop, even at 1.9v. This is above my voltage comfort zone anyway, so I'll just have to cope with 1.05GHz. I'll get by.
If you're interested, here's some Sandra shots of the machine at 124x8.5. This is with the HTL PC100 RAM running at 124, CAS3, "Turbo" timing. I also have a 60mm fan mounted on the waterjacket, blowing down onto the KX133 northbridge "Greenie" heatsink. This is because, having no CPU fans, there's less airflow in that area than there would normally be and that heatsink gets pretty warm at 124MHz FSB.
|
|
|
| CPU | Memory | Multimedia |
Recovery
If you do find yourself in
trouble, facing a blank screen due to over-ambitious settings
perhaps, the KA7 offers you a few options. Firstly, you can just
turn it off and wait a few minutes - it will sometimes detect
that Something Bad has happened and boot up with default settings.
This doesn't work often enough for you to rely on, though. You
can turn it off, and, holding down the Insert key, turn it back
on. This works probably 90% of the time first go, booting up into
the BIOS setup screen at some safe speed but, and this is nice,
retaining the settings you were attempting - so you don't have
to add them all back in one-by-one, you can just set the one problematic
setting back to something a little saner. Finally, if all that
doesn't work, you can reset the CMOS via the onboard jumper. I
did this a couple of times and got the result you'd expect, a
bootup at default speed, warning messages about my CPU setting,
everything back to defaults in the setup.
Next up, I examine the board's performance at stock speeds and compare it to the Asus K7V.