Overclocking Dell BTX Computers

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Overclocking Computers Dell
william p
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Why overclock a Dell? Because they're there. Millions of them in fact. Just about every Dell, HP, Gateway, Acer, etc. Intel computer for almost 10 years was a BTX. Many of them are being sold now as refurbished computers for less than you can buy an operating system license. BTX was originally a very high performance specification. It was made to allow Intel Pentium4 "Netburst" CPUs to reach speeds as high as 3.8GHz, and PentiumD 135W dual cores to run 3.2GHz. The 45* twisted CPU socket allowed shorter traces to the chipset. Speed like that weren't achieved again until the chipset was moved onto the CPU with the i series. Unfortunately by the time the 45nm LGA775s came along, or even the later 65W Core2Quads the BTX platform had been gutted by the OEMs so they only run 95W business CPUs (except for some workstations).

Overclocking, like any other sport or hobby, has it's dangers and you participate at your own risk. I would advise against doing anything you see here to a computer you don't actually own, or have the owners permission to modify.

So what is a BTX? BTX "was" a form factor. Originally BTX was intended to be like ATX where parts were interchangeable between computers. Intel hoped it would replace ATX. For whatever reason the parts makers who make cases, and motherboards for the aftermarket didn't go along with this and kept making ATX parts. There are no BTX aftermarket parts. So adapting and modifying comes with the terriitory. When Intel stopped "supporting" the BTX specification in 2006. The OEM computer companies started changing it so that only their proprietary parts could be used.
So parts swapping is much harder. Almost impossible in fact.

Are they any good? In some ways they're very good. They tend to be over-engineered, meaning they're very dependable and that's why they're found in businesses and offices everywhere. They run very cool. BTX was designed specifically to cool some of the fastest clocked and power hungry CPUs ever made. The Pentium4s ran at clocks up to 3.8Ghz almost 10 years ago, PentiumDs (dual core P4s) were 130 Watts, same as Quad core Xeons and core2 Extremes.


What's so cool about BTX? ONE BIG FAN! Back in the day CPUs used most of the power. GPUs were a minor accessory. 256mb typically. Single slot often with no fan. In BTX everything was to be cooled by ONE BIG FAN! The classic BTX fan is the Delta AFC1212DE. It looks almost normal. 120mm diameter, a little chubby being 38mm thick. So whats the big deal? It draws 1.6Amps, a good ATX fan draws .25Amps. It's a PWM fan so it only runs fast if it needs to. It's kind of like the Clark Kent of fans. Don't stick your fingers in one they will draw blood. BTX specifies where the fan, the VRM chips, The CPU, the memory slots ,the expansion slots and just about everything else will go. This means the fan Pulls air in the front of the case and blows on the VRM chips first, then the CPU heatsink which is in a plastic shroud so all the air goes through it. Then the air cools everything else by positive case pressure. The motherboard is mounted on the left side of the case. The video card usually went in the top slot so the fan blew air right past it. There was a column of cooling air from the front to the rear of the case. That's how you tell a BTX, the plastic shroud ducting air from the front mounted fan past the CPU.

If they're so great why does everybody hate them.
1-Parts interchangeability is lousy
2- No aftermarket performance parts made for them
3- They were designed by the OEMs to not be modified. Especially BIOS settings.
Why? Think about it , if you just sold a company 50,000 computers, that means 50,000 people operating the computers. Somebody's going to want to "improve" or maybe even damage a computer. They're all under extended warranty or service contract of some kind. The Businesses, AND the OEM don't want those problems.

So are you saying they cant be overclocked? No I'm not saying that at all. There have been people overclocking them for years. They just can't be overclocked in the normal way.

Here's a Dell Dimension E520 BTX CPU-Z validation. The computer was built in 2006. It had an E6300 CPU 1.86Ghz,2 GB RAM and a 256MB video card. http://valid.x86.fr/bg4n0r

It now has a QX6800 Core2extreme Quad core (2.93GHZ,130W) overclocked to 3.72Ghz for daily use, and has gone 3.99Ghz for a validation run. The motherboard (0WG864) has never been out of it.
8GB DDR2 RAM @ 800Mhz. Win7 64bit, 240GB SSD
GTX750Ti O/C video card. I'm writing this article on it right now.
It's had a R9-285 ITX, and it's going to get a GTX1050Ti4GB soon.

So how do you overclock a BTX?
It depends on which BTX you're starting with. Some are better than others and some you can't do anything with at all. Basically it depends on the motherboard.

You can see a lot just by looking (Yogi Behra).
If you're confronted with a BTX, Google the Make, and Model/ type of case/motherboard/images. Put the mouse on images until you find one with a high resolution, then open the image.

1- Look at the VRM area, always between the CPU (which is mounted at a 45* angle) and the edge of the MB. Count the chokes there. Chokes look like round beads with copper wire wound around them. There will be 3, or 4. If there are 4 it means 4 phase VRM and a high powered board. 3 means it won't run the biggest CPUs at the highest speeds. I always assume a 95W limit on newer 3 phase boards unless I see another limit listed somewhere, such as support for older Quad CPUs. Newer CPUs don't need more than that and the OEMs adjusted accordingly. With a fan wiring modification listed later they might have more power available, But I haven't tested this. It will depend on where the weakest link is.
Edit: I stand corrected here. Justajohn reports Dell Precision T3400 QX9650 @ 4 GHz. Prime 95 for 5 hours with 3 phase VRM. So it doesn't seem to be limiting the newer Quads. 2/21/2016
Known 4 phase MB (all 65nm Core2) E520/Deimension 9200 /e520/9200c (SFF) XPS410, XPS210 (SFF) XPS710, and XPS720 (45nm C2X 400fsb unlocked BIOS).

2- Look for "missing parts". Is there a place for 4 memory slots but only 2 are installed? Is there a place for a PCIe video slot, but no socket there to put it in? This means it was built to a price. Yes some of them have no video slot.

3- Look at where the video card goes.Is it in the top slot. Then the video card is going to be blocked by the cooling shroud with a lot of newer video cards. Is there a PCI, or PCI 1x slot, then the 16X slot in the 2nd position. This is very good, it means a 2 slot video cards can fit. Probably a high end MB.

4- What type of case is it for? There are 4 basic types.

Tower, mid tower, mini tower cases are all about the same (in the same make ,model computer) except the smaller they get the fewer expansion slots they have. Mini Towers( MT) almost always have 4 slots. The bigger cases are often the ones with room for 2 slot video cards, or even 2 video slots, and high powered motherboards because they were more expensive computers to begin with.

The next is the Desktop( DT) they are similar to mini towers except they are a little thinner to lie flat on a desk. This can limit cooler options, and video card dimensions. 4 expansion slots are normal here also.

The next is the Small form factor (SFF). This is thinner and narrower than the Desktop. It requires low profile coolers, and expansion cards. PSUs are often custom parts with limited options available. Some of them accept fast quad cores, and large memory capacities. But there are also some with 25W "server" video slots.

Then there's the Ultra Small Form Factor (USFF). Just about everything for these is compromised to allow a smaller computer. many of them have no GPU slot.

5- Go to userbenchmark.com and search for the system you're interested in. You will see what others have gotten to work. You may also notice things like almost no AMD GPUs, or some 120W Xeons running, or even some pinmodded Q6600@ 3GHz.if you look close enough. You may find one with more RAM than expected, another with a higher powered CPU, and another with a high end GPU. But maybe none fo them with all 3. See what CPUs score highest, and what GPUs score best also. If you see Q9550, but no Q9650 that computer may not support newer steppings of those CPUs. The Dimension E520 can only be found under DM061. That's how it identifies itself there. If you already have the computer run it and see what you get. You can see a couple overclocked QX6800 (44%) outscoring the Q9650 (40%) in the newer Optis. Precision T3400 has some 4.15Ghz QX9650 scoring 57% and it is a pure BTX Mid Tower Dell.
http://www.userbenchmark.com/



THE DREADED BTX BIOS
It is what it is.. It's locked, so get used to it. No overclock setting available. About all you need to know is processor support, FSB support, Memory type,speed,and capacity.They don't recognize Core2X chips. My BIOS says my QX6800 is a Q6800 (I don't think there really is such a thing). It runs and that's all I care about. My old P4 era 4 phase board got a BIOS update for Core2 processors. Many others didn't. Some only support 65nm 1066fsb chips (mine) some only 45nm chips, some list both. Always get the latest BIOS available. Mine is from 2007. Dell often lists memory capacity as 1/2 of actual capacity. Go to Crucial.com for the real limit.
There are people who modify BIOSs, the consensus is that it can't be done on Dell, or Intel BIOS. One mod that is done is to install Xeon microcode into a BIOS. There are a few exceptions. Some of the XPS models allow overclocking of Core2 Extremes.

I'm sorry that took so long but it's not easy to describe half the computers in the world in 100 words or less.

VARIOUS METHODS OF OVERCLOCKING A BTX. ( Not in any particular order).

1- Software control of the Front Side Bus FSB.
This allows overclocking of CPUs with locked multipliers (almost all CPUs are this way).
Programs are Clockgen, SetFSB, and some others. They need you to identify the PLL chip (phase lock loop) and enter it's number into the program, then it communicates with that chip to alter the speed of the FSB, Usually you can change the memory bus speed separately. CPU speed is Multiplier times FSB So 10X266Mhz=2.66Ghz, 10X300Mhz=3Ghz. Incremental increases are an advantage of this method.
Generally Voltage needs to be increased to stabilize the CPU with faster clock speeds, and cooling increased to compensate. In Core2Extreme it is possible to do this in software,and the voltage needs to be applied before the higher speed is set. I never used these programs successfully myself so do some research.
Some computers have a TME lock on the PLL to prevent overclocking. iI the computer supports 333fsb then 266 fsb CPUs can be pinmodded to the333fsb limit. if you have a computer that supports Core2 extreme CPUs then you can underclock the fsb and add another multiplier to get smaller increments of clock speed.

2- The "Pin Mod" method Older CPUs had pins, LGA775 has pads but Pin Mod is what it's called. Pin Modding requires you to change the connections between the pads on the CPU ( actually it works by changing the connection between the terminals in the CPU socket). Sometimes blocking them with tape to break a connection, sometimes to connect pads with conductive metal tape, or electrically conductive "paint" pens. The overclock comes from taking advantage of a difference in FSB speed between the motherboard (higher) and the CPU (lower). Not incremental, but very stable and effective. 266 to 333 to 400 fsb can all be done with tape only.
Example E7500 2.93Ghz 1066fsb, Pinmod to MB 1333fsb= 3.66Ghz. Actually a sweet spot for this CPU needing no voltage increase, and not much more heat produced.(of course QX6800 ,or X6800 would be this speed also.also)
Example 2 Q6700 2.66Ghz 1066fsb to 1333=3.32Ghz. There have been been Pin Mods from 800fsb to 1333 turning mild mannered Core2 duos into 4Ghz screamers. Voltage can be changed by Pin Mod also. This can be useful with FSB method also. My E520 MB didn't have a faster FSB to use with My Core2 Quad so I had to find something else. Some XPS models, and Workstations had 400FSB support due to having X48, or X38 chipsets. XPS430 Q9550 @ 3.4GHz confirmed.
Here is the LGA 775 pinout. it's looking at the socket, not the CPU pin side so it's reversed.
http://rayer.g6.cz/hardware/core2/core2.gif
Here is the BSEL chart.
http://images.people.overclockers.ru/113487.png

The other pinmod is the VID mod. It's something of a lost art. It started back in the Pentium 4 days and the early LGA 771 Xeons. The Xeon LGA771 BSEL, and VID pinouts are the same as Core2 LGA 775 so don't ignore anything you find there. This is much more complex due to the number of Voltage settings available, the number of pins involved, and the different Voltages even the same CPUs came set at. First find the default Voltage your CPU is set at. Next look up your CPU and see Intels maximum Voltage. This isn't a real limit but at least you'll know when you're doing something risky. To raise a pin that's low tape it. This breaks the circuit and =0. To lower a pin that's set high connect it to VSS with metal tape or foil. Connecting to ground completes the circuit and =1. It may help to insulate the CPU side of the pin first to isolate the previous connection there., It's the MB pins you need to spoof, not the CPU. Map out the pin setting for your default Voltage and find one close to the maximum( or not) that requires fewer, or simpler changes.
Page 15 here has the VID chart for 45nm CPUs
https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/core2-duo-e8000-e7000-datasheet.pdf
or page 15 here fore 65nm CPUs
https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/core2-duo-e8000-e7000-datasheet.pdf

3- Something Else. Core2 Extreme method. This is another software overclock. It requires a Core2 Extreme unlocked multiplier CPU. These used to be $1000 chips. Now that Xeons have captured the hearts of ATX overclockers they are $100 for the best of them and $30-$40 will get you in the game. The software was designed to extend laptop battery life by undervolting, and underclocking CPUs. This means it controls voltage in Windows, and controls multiplier just like Speedstep. It's called "Throttlestop" and it's free from TechPowerup, and other sites. With an unlocked CPU it can increase multiplier also in increments of FSB speed. It is very feature rich. It has readouts for each core temp.,GPU temp., Core % usage each core, maximum temperature reached is recorded and displayed. A button to toggle Speedstep off and on. It's worth having to monitor any other overclock you might have.
Set voltage high first or it might crash with an unstable setting saved, which is not good. WARNING It changes multiplier when you select it, not when you save it. Speeds with a 266fsb are 10X=2.66Ghz,11X=2.93Ghz,12X=3.2Ghz,13X=3.45Ghz,14X=3.72Ghz, and 15x=3.999Ghz.
With 333fsb 9X=3.00Ghz 10X=3.33Ghz,11X=3.66, 12X=3.99Ghz.
Edit: Justajohn reports QX9650 supports 1/2 multiplier steps on 333fsb. QX6850 has full steps.
This almost always requires a computer that supports 130W CPUs. The optiplex 745, Dimension e520,9200 XPS series, and worksations qualify. Most optiplexes don't support over 95W CPUs. The 65W X6800 2 core tt might work in those for retro gamers..


4- Xeon swapping.
X3xxx Xeons are LGA775 CPUs. They are equal to or better than high end Core2 chips.
Edit: there are a few LGA771 X3xxx Xeons. 2/21/2016
X5xxx Xeons are LGA771 CPUs This requires an adapter, which is piece of tape with a Pin Mod built into it, and the removal of 2 locating pins in the CPU socket. Some of them are so close to high end Core2s they work without a BIOS microcode update. Delidded.com has a list of Xeons, and information on MB and chipset compatibility. They overclock very well in ATX computers. But they don't have unlocked multipliers, and they almost always have the fastest FSB already. So 2 of the 3 overclocking methods listed above won't work in a BTX. They can be inexpensive equivalents to rare and expensive versions of Core2 chips. If they work. Some are Dual Core and can be used on a lower powered MB. They also tend to draw less current than equal Core2 chips and may allow a Quad Core to be used in an application where it might not be possible otherwise.
There are a few 65W core2Quads Q9550s,Q9505s, and a few Xeons also. They overclock very well and give some hope to those with 95W MB limits.
http://www.delidded.com/
Delidded is a very good resource for MB limits, chipset issues, CPU steppings. etc.

CPU STEPPINGS
When a CPU is introduced it gets an Sxxxx number (or Qxxx engineering sample ES which belong to Intel and you aren't supposed to have). If there are improvements made then a new S code is given. This can be important. A newer one may use less power, run cooler, and overclock better. The classic example is the Q6600 which came in B3 stepping SL9UM, or the much better SLACR G0 stepping. Sometimes a BIOS doesn't support the newer stepping so the older one is needed. The QX9650 comes in C0 SLAN3, and SLAWN C1 stepping. But the SLAWN gets a different CPUID number 10677 while the SLAN3 keeps the 10676 ID#. Some BIOS may recognize one and not the other. Some have more than 2 steppings, and more than 2 CPUID numbers.
http://www.delidded.com/lga-771-775-cpus/#steppings
Usually you would want the latest stepping unless there's a reason not to use it. You need to shop by the Sxxxx code to be sure you get the CPU that you want.

A FEW WORDS ABOUT MEMORY SPEED DDR2 vs DDR3
DDR2 memory has lower latency, and is faster at the same clock speed than DDR3. DDR3 can run at higher clock speeds than DDR2. Basically DDR2-800 is as fast as DDR3 -1066. These are the 2 speeds you will most commonly find in BTX computers. So don't worry about this too much.

COOLING AN OVERCLOCKED DELL BTX

COOLERS
There are 2 heatpipe coolers that work well. The first is an old PentiumD part D9729 which bolts into a lot of Dimension and Optiplex computers. It has 3 heatpipes (6 nipples at top)..
The second is newer and came from some midtower, and workstation series computers T9303. Some newer Optis can use the T9303, they are similar size and mount the same. The t9303 has the heatpipes evenly spaced across the cooler, the D9729 has them in groups of 3 on each side. If the holes in the top of the cover are cut to fit the nipples they are interchangeable. The T9303 cools the GPU better due to more air flow through it. That's the one I used in the 3.99Ghz validation run. They trade for $10-$15 on ebay.
There is RW134 for desktops, and JP911 for SFF. Sometimes the smaller sized aluminum heatsinks are used in the Mini Towers with low end 2 core CPUs.

FANS

DO NOT ATTACH ANY OF THESE FANS TO AN ATX MOTHERBOARD HEADER

The only problem with the Delta fan is it gets loud when it speeds up to cool an overclocked Core2Quad. Even at 50% it's loud. It also waits too long to start cooling. It speeds up at 74*C and has no trouble pulling the temp. back down to 68*C. But that's not what we really want. Now this is only running 4X Prime 95 @ 3.45GHz, or 3X Prime 95@3.72Ghz. Below that it's just fine. So what to do? There are a lot of faster Delta fans that fit. Some of them draw up to 5 amps..
https://www.youtube.com/watch?v=Wqc72EOuteU These fans come in speeds from 3000 to 7000 rpm
What they do in a BTX is they speed up sooner and keep the temperature low in the first place, but noise is still an issue. My solution was the slower running 3.4A GFB1212VHG 120mmX50mm fan with 2x 1.7A motors.
https://www.youtube.com/watch?v=sIJUYHetJWs ( GFB1212VHW is even bigger 120mmX76mm)
Lots of air at low speeds. The 3.99Ghz was done with the fan @100% speed so it's not for normal use. Disconnecting the Blue PWM wire sends the fan to 100% speed on any of these fans.
Bigger fans need to be run off of a Molex, not the MB header, leave the PWM ( blue) wire, and the tach (white) wire on the MB. There will be a fan error message at boot. It can be cleared from the BIOS in SYSLOG/ Event Log. I just don't reboot. I put my computer to sleep. it wakes up fast, and goes right back to where I was. If a Windows update reboots my computer then I clean out the SYSLOG and continue as before. This is not a fatal error, you can hit F1 and continue the boot process without clearing the BIOS error. cdoublejj at Overclock.netreports that a small chipset fan with the blades cut off can be wired in to prevent this error messabe. Be sure and clear the error before testing or you won't be able to tell if it works.
When I was trying for 3.45Ghz, I took the fan off the MB and found I needed less volts at 3.45Ghz, and had more available to run 3.72Ghz. It was worth a whole multiplier in my overclock! BTX speed secret right there! Even without the fan swap, removing the fan power from the motherboard should be considered. When the CPU gets hot the fan speeds up, and it pulls current away from the CPU which can cause a crash. Worth .1V (.05V lower starting voltage, and .05V higher voltage available). Another fan is the AFC1512DG it replaces the whole fan and housing in Most dell BTX it's 150mmx 50mm and draws 1.8A. It plugs into the MB header and is quieter then the 120mm fans.

MORE COOLING -This is normal O.C stuff so you might already know it.
Heatsink the MOSFETS. each choke in the VRM will have (usually 3 ) some square black transistors about 1/4" square by each of them. These are the MOSFETS. They get hotter than normal when overclocked. They provide the increased voltage to the CPU. Attaching heatsinks to them is a big improvement. I got .05V extra current available to my CPU from doing this. It made 1 more multiplier possible. Even the little 4 pin copper Enzotech heatsinks will work (that's what I used). The pins are just like copper wires and can be bent to clear MB components as needed. The Nothbridge and Southbridge chips can use upgraded cooling also.

LAPPING THE COOLER AND CPU More normal O/C stuff.

They need to be as flat and smooth as possible. There are tutorials on how to do this. If the heat stays in the CPU it defeats the purpose of everything else. Good Thermal Interface Material (TIM) makes a big difference too . There are comparison tests available online.

WHAT MORE COULD THERE BE

Video cards
Basically unless you have a MB with the GPU socket in 2nd spot a large 2 slot 2 fan video card wont fit. Long thin cards fit., short (6 3/4" long) thick cards fit, IF they're single slot. The Mid Tower computers usually have room for a full length 2 slot GPU and a 6 pin PCIe power connector. Dimension 9200 is one. the Workstations usually have 2 GPU slots that take 2 large cards. T3400 is a BTX Workstation.

Zotac has recently released a single slot (bracket) short card that fits BTX Mimi Towers.
The GTX1050 Mini 2GB, and the GTX1050Ti Mini 4GB. it's 2 slots wide at the cooler, and runs off of the Dell PSU (no PCIe cable needed). This makes these computers 1080P capable.
The low profile versions are a mixed blessing. The all seem to have a hard mounted DVI port in the 2nd slot position. This will require a case mod to clear it, and in some situations may interfere with MB rear I/O riser of some kind.
.
Can it be made to fit?
Short 2 slot cards can be made to fit. Remove the bracket, cut the 2nd slot part off, then reinstall the bracket.Trim the plastic cover so air goes out the side towards the air vents. 5 minutes work. If the card has electrical parts on the 2nd slot then you cut the second slot into the case, and just trim the top and bottom tabs off of the 2nd slot bracket. The cut off peice can be installed behind the video card to let heat out. Many Low Profile cards come with a single slot tall bracket. This can avoid modifications. Newer cards have DVI on the 2nd slot which can't be moved, older cards with VGA there are cabled and can be moved or removed as needed.

ITX video cards.

These go up to GTX970. They almost fit in a BTX. The mod above is required, and grinding some clearance in the cooling fins at the front to clear the mounting bracket of the cooling shroud.
Edit: I'm running ITX R9-285 in Dell E520. The video card doesn't support the video resolution the 2007 Dell BIOS needs. It runs great, but I can't enter BIOS setup. Nvidia doesn't have this problem. There are more powerful ITX cards becoming available R9 Fury Nano which I guess is based on GTX980. The problem affects radeons from R9-38xx (285) and up. I had one report of MSI afterburner fixing this.

UEFI Video Card BIOS

Some new video cards require UEFI BIOS. Some newer BTX computer have it. My Sapphire
R9-285 has a switch to use either one. On older BTXs check for this issue with a new video card.
My E520 doesn't have EUFI, neither does my PNY GTX750 Ti O/C. Optiplex 780 and up are UEFI

VIDEO CARD AIRFLOW

Some video cards send heated air past the cooling shroud towards the front where the fan can't remove it. It collects in the expansion slot area and hinders GPU cooling. A small "cyclone" type expansion slot exhaust blower will solve this problem. The mid towers and workstations used a small front fan and vented expansion slot covers to provide airflow in the expansion slot area. The vented covers might be all that's required.

RECOMMENDATION
The new Zotac GTX 1050(Ti) Mini looks like it was made for BTX Mini Towers. A full 1080P card that doesn't require a PSU purchase.

VIDEO RAM

Since we're interested in performance here, don't bother with any video card that doesn't have DDR5 memory. DDR3 is just too slow for this purpose.

Now that there are getting to be 4GB video cards in this market you need to be aware that they share system RAM and if possible 12GB RAM or more is suggested. Most BTX with DDR2, or 2 DDR3 memory slots only support 8GB. Unigine Valley is an example of a program that's very memory intensive. Many others won't have any problems. But with 8GB RAM a 2GB GPU is the safe bet. It will be a little slower everywhere but it won't cause a RAM bottleneck as easily.

The GTX750 series GPU was the go to card for BTX computers. It comes in various sizes, single slot, low profile, 2 slot single fan. It draws 60W of power which is under the PCIe16x limit of 75W. So no power connector is usually required. This saves the cost of replacing the PSU. Mine can run Unigine Valley on Ultra at 60+fps all day long. A good performance for an inexpensive card.
many times this is still the card for low profile BTX because the LOw profile 1050s seem to have hard mounted DVI port in the 2nd slot. The 750s have a cabled VGA that can be moved.

32BIT OS Rules.

If you are running 32 bit OS for some reason. Then there are some rules to follow, and of course some you will need to break. The old rule was 4GB RAM limit for 32 bit OS. 32bit Windows can only adress 3.5GB RAM. The MB and 256MB video card could use the rest. But if you put in a modern 2GB GPU and it "shares" 2 GB system memory you will have a problem. In this situation go ahead and install 6GB RAM. The GPU will use it from the top adresses down, and the OS will have it's 4GB. If there is an actual 4GB memory capacity limit (2 RAM slot DDR2) then use a 1GB Video Card. GTX750 can be found with this capacity.

A WORD ON BTX PSUs

BTX PSUs tend to be closely matched to the computers they came in. Computers with more drive bays and expansion slots got bigger PSUs. They also tend to be rated very conservatively. A customer could expect to load a computer up with every option and then run it 24/7 and have no problems.The OEMs didn't want to have PSU failures or the damage to systems that can cause. They are quality parts. Add about 50W-75W to the rating of these PSU to get the equivalent to advertised enthusiast PSUs. So if you need to upgrade one of these get one at least 150W higher than what you're replacing. In Tower, and Deskltop system the OEM PSU can usually be replaced The 24 pin power connector came from BTX. But all it takes is one proprietary power connector on a MB to mess this up. So you do need to be careful. SFF, and USFF always have special PSUs, and due to no larger versions of these, upgrades are few and far between. If your video card says 350W PSU required, and you have a Dell 305W PSU. I would try it first. There are a few Dell PSUs that are of interest. The dell T3400 375W PSU provides a 6 pin PCIe cable and 4 pin CPU connector. It fits in Optis etc. It's about 1/2" taller so make sure there's space for it. The XPS 420/430 #L425P-00 it has 2x 6 pin PCIe cables. These will have cables the right length for BTX computers. But not for ATX.

DT PSUs

There are some 350W PSUs for the desktop models. Seasonic makes an OEM type TFX 350 with no GPU connector, and a TFX GT350 with a 6 pin. (always out of stock it seems). Since the good low profile GPUs (GTX 1050Ti) don't need the 6 pin the OEM should be OK. This is a quality PSU according to Johnnyguru.

SFF PSUs

The SFF PSUs can seem to be puny and almost always under rated for a modern GPU. They are small because the SFF doesn't have the drive bays and expansion slots that towers have. Also the almost universal 95W CPU limit means 35W less than other computers due to that. Usually they're OK. Some SFF have a 25W GPU limit on the 16xPCIe slot. Some people have run GTX750s in them anyway. But the risk is yours. Here's the good news. Dimension 9200c, and XPS210 were SSF versions of the Dimension E520/ Dimension 9200 family and came with 130W PentiumD CPUs. The PSU was rated 275W. Look at photos and see if ti will fit your situation. A lot of the things I post here you might be the first one to try. I haven't bothered with SFF myself, but I get a lot of questions at Tomshardware Forum about these so the interest is there.

SSD

I have seen complaints about putting in an SSD and it fails within a week. SSDs didn't exist when most BTXs were made. In Accessories/ System Tools look for Auto Defrag setting and turn it off. On both my Dells this was still on by default after I installed an SSD, even in Windows7. Defragmentation has to do with relocating data on a spinning platter. You don't want it on an SSD.

SSHD

Hybrid drives have the large capacity of HDD and the speed of SSD because they usually have an 8GB SSD cache sytem. Large, inexpensive. Good for a budget build where full SSD would be too expensive. They come in 2.5" size for laptops also.

HERE ARE SOME RESULTS
Dell Dimension E520, Pentium D rated, 4 phase MB up to 3.99GHz, Qx6800, runs 3.72 GHz stable. 8GB RAM- modified air cooling
Dell Precision T 3400, 3 phase MB, mid tower, supports ATI Crossfire 2X GPU, QX9650 4.15Ghz stable. 16GB RAM- Stock cooling.
Dell Optiplex 745, Pentium D rated 3 phase MB, QX6800 3.45GHz. 8GB RAM- stock cooling.
Stock cooling is Dell heatpipe cooler w/ stock fan(s).

If your interested in working with one of these (overclocking or not) you can go to userbenchmark.com and enter the system your interested in and see what people are running. If you see almost no newer Radeons then that's a warning. You may also see some Xeons, Most of them with X5xxx numbers are LGA771 and need an adapter. X3xxx are (mostly) LGA775 already.
Typically a Q9650 with a GTX1050 GPU will score about 40% of all systems tested. Overclocked machines will get into the 50% range. A good examle of a Xeon is the E5450 which is an LGA771 version of the Q9650 but draws 80 watts versus 95W. For some reason the Dimension E520 only shows up by it's model# DM061. So if you can't find your system you might try other decsriptors.

WHAT HAPPENED TO BTX
BTX came and went with LGA775. The cranked CPU made for shorter leads to the Nothbridge and helped allow 3.8GHz speeds for Pentium 4 CPUs. When the chipset and memory controller went onto the CPU die it no longer served any purpose.

WHAT NEXT

Throttlestop locked BIOS overclocking beyond LGA775

There are some unlocked CPUs that could be of interest to overclockers.
Dell T3500 workstation LGA1366 W3680/90 are unlocked 6 core Xeons.
Intel i5-2500K is a 95W 4 core cpu that can run in newer Dells (OC unverified at this time)
Intel G3258 is an unlocked 53W CPU 2 core (unverified)
i7-875K si 95W unlocked 4 core CPU (unverified)
i5-655K is unlocked 2 core CPU under 95W. ( unverified)
"unverified" means that I don't know of any examples of an overclock being done with a locked BIOS computer. They ARE unlocked CPUs.