If you buy an i845 based P4 supporting motherboard you can reuse the old SDRAM,
however I strongly suggest you do not! Performance of a 1.5Ghz P4 on the i845 is very poor. (About the same as a 1 Ghz P3 actually.)
Other issues going with a P4:
A. Your existing case and powersupply are not going to work. Power supplies for a P4 need to have an extra 4 pin 12 volt power connector. It's also likely your case will not provide sufficient cooling and/or processor heatsink mounting holes.
If you go with a KT133a based Athlon board and reuse your old SDRAM you are again shooting yourself in the foot performance wise. You may also need a new (better cooled) case and 300W AMD approved powersupply. (As a side note, some early Abit KT7a boards DO NOT support the new Athlon XP. This is the only kt133a based board with this limitation.)
Also, your Radeon card is a bottleneck to games performance with any option listed below.
As I see it you have a few options:
(You will need to format and reinstall EVERYTHING unless you can find another BH6.)
1. Try to find an old socket 370 motherboard that supports your P3 and just replace the board. This would be the lowest cost and hassle option. If you can find a BH6 you won't have to reinstall everything. An 850 Mhz P3 system is hardly "obsolete" for running just about anything you can throw at it, so this is not a terrible option. Performance of this option would be identical to what you are used to. Total cost of this option (estimate): $120
2. Buy an i845 based board, new P4 supporting case, P4 1.5Ghz, (possibly modem, as new boards do not have ISA slots). Reuse video, sound, ram, HD, etc. You need to be aware that all P4 supporting motherboards only support 1.5v agp cards, and even attempting to use a 3V AgP card WILL destroy the motherboard. Your Radeon card could be either type, you need to determine this if you go this option!!! It's also important to note that SDRAM destroys the performance of the P4. In addition your Radeon card is already the bottleneck in your system as far as AH is concerned. Performance of this option would be marginally faster in Windows applications and virtually identical in AH. Windows (and thus all programs and data) will have to be reloaded. Estimated Costs: i845 Motherboard $150, P4 supporting case and powersupply $80 minimum, modem (if applicable) $30 - $80, P4 1.5 Ghz socket 478 CPU $180, and Pentium 4 heatsink and fan $30 =
$480 MINIMUM (Keep in mind that you MAY also need to replace the video card if it is NOT AGP 1.5V compliant. You will also need to reload Windows etc.)
3. Go with a
REAL P4 based system using either DDR SDRAM or Rambus RDRAM. This means you will need all of the above stated for the i845, but you will also need to buy either DDR ram and a SIS 635 or Intel i845D (D meaning DDR ram supporting) or Rambus RDRAM and an Intel i850 based board. The Sis 635 based boards are available, the i845D boards have not yet hit the shelves, but can be ordered. Asus makes boards based on all three of these chips for comparison. Performance in most applications would be noticably faster than your old system (though not an extreme performance boost by any means). AH and game performance would be small, as your Radeon card would be limiting your performance once again. Windows and all applications will once again have to be reloaded. Cost would be the $480 minimum again + the cost of RAM. (768 MB is excessive and isn't gaining you anything if you are running win98 or ME.) For 512 Mb of DDR ram (2 x 256 MB) you are going to spend around $150. RAMBUS PC 800 Rdram will cost you $200 minimum (2 x 256 MB). Total costs would be around $650 - $750.
4. Go the AMD route and use my new personal favorite MSI K7N420 Pro board. You will again need to buy DDR ram, powersupply (and likely case), CPU (Athlon XP 1600+) and CPU heatsink, and motherboard. Total system performance would be noticibly faster than any of the above options. Gaming performance is once again bottlenecked by the Radeon card and will only be marginally faster than your old system. Windows will once again have to be reloaded. Again, only 1.5v AGP cards are supported. Total Costs: Case (includes AMD Approved 300W power supply) $80, Cpu (XP 1600+) $130, Heatsink for CPU $20, modem (if needed) $30 - $80, 512 Mb (2 x 256 MB) PC 2100 DDR ram $150, MSI K7N420 PRO motherboard - $200 = $610.
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My personal recommendation (I.E. What I would do) would be to get another BH6 in the "bargin bin" somewhere and just replace the motherboard. Reusing that Radeon is going to limit your gaming performance. Forcing SDRAM to be used also severely limits performance on the P4, and reduces it to a lesser degree on the Athlon. No matter what, I would not reuse the ram in a new system for upgradability and performance reasons.
I guarantee you that if you go out and buy the an SDRAM supporting P4 motherboard (which will use the Intel i845 chipset) and a P4 1.5 Ghz and reuse that Radeon card you will not see more than a 5% increase in your AH framerate. It's just not a cost effective upgrade given your current system specs.
If you really wanted to go with a P4 or Athlon system, I'd also dump the Radeon and buy a new video card, otherwise your aren't going to see a significant performance increase in games. Anandtech (
www.anandtech.com ) posts regular CPU, video card, memory, and motherboard price guides if you were interested in knowing how much this would cost. (Keep shipping costs in mind.) Realistically you could reuse your: floppy drive, CD Drive (drives), ribbon cables, hard drive, sound card, and (if it's a PCI or external) your modem. You should get yourself a new case that includes an approved powersupply for whatever type CPU you want to use.
Hopefully I've helped you some here.
