RAM modules compatible with motherboards based on the i440bx chipset

This FAQ will help you to find out which ram modules will work in your motherboard based on the bx chipset. It will not cover problems specific to one board, but in general all boards based on the bx chipset support the same modules. There are a lot of boards based on this chipset, examples are the Asus P2b, cubx, Abit BP6, BE6-II and countless others.


Table of Content

General Questions about RAM compatibility with boards based on the bx chipset

Q: Only PC133 Dimms are available. But the manual states I need PC100 Dimms?
Q: Can I mix PC133 Dimms and PC100 Dimms or even PC66 Dimms?

Q: What are the differences between registered/buffered/unbuffered memory modules?
Q: Do I need registered memory?

Q: Can I mix registered memory with "normal" unbuffered memory?
Q: Do I need ECC memory?

Q: Can I mix ECC and non-ECC memory?

Q: Can I use DDR memory or even some old EDO modules?

Q: What module sizes are supported on my bx-based board?
Q: What is the maximum amount of ram my board supports?
Q: How can I find out what type of Dimm I have in my computer?

Questions specific about the compatibility with 256MB Dimm modules

Q: I've just bought some 256MB "high density" module with 16 chips on it and only half of the ram gets recognized. What's wrong?
Q: My vendor lists a 256MB module as PC133, 32Mx64, will it work?
Q: I don't quite understand which 256MB modules will run. Can you explain a bit more on those 16Mx8 etc. terms?
Q: My 256MB module has 8 chips on each side of the module, so it is obviously double-sided?

Other problems/questions

Q: I have more than 512MB memory and the board seems to recognize all of it, but Windows acts strangely, telling me that I don't have enough ram or just doesn't start some applications. Is my ram or board defective?
Q: My computer is a bit unstable and I suspect I have some bad ram, but the BIOS ram test doesn't find any errors. Is there a better method to test the ram?
Q: I have a P2, more than 512MB memory which all gets recognized but my computer runs really slow. What's wrong?
Q: Where can I find even more information about the bx chipset?
Q: I have no idea what you are talking about in this FAQ, can't you just tell me if the ram I'm going to purchase will work?
Q: What brand of ram do you recommend?



Q: Only PC133 Dimms are available. But the manual states I need PC100 Dimms?
A: No, you don't. Every PC133 Dimm is backwards compatible to PC100 (and even PC66).

Q: Can I mix PC133 Dimms and PC100 Dimms or even PC66 Dimms?
A: Yes. Usually it is recommended to use the same ram modules for all ram slots, but it should work without problems if you mix different brands, speed grades, sizes. If you use a FSB of 100Mhz, you can't use PC66 dimms, and if you overclock your FSB to 133Mhz, you need PC133 modules (you can of course try to use modules not rated for that speed, but you shouldn't be surprised if it doesn't work stable).

Q: What are the differences between registered/buffered/unbuffered memory modules?
A: Registered modules have additional registers, which delay all addressess transferred to the module by one cycle. This is done to decouple the ram chips from the memory bus, so a module can have more chips (the bus load will not increase if more ram chips are present). Because of  that, registered modules are available in higher capacities, but of course you can't use these high capacity modules on a bx-based board.You can recognize registered modules physically by looking at them. If there are one or more (small) chips on them apart from the ram chips, then it is a registered module.
Buffered modules are similar, but instead of registers, they contain buffers, the difference is that a register is clocked, and a buffer is not. EDO and FPM modules can be buffered or unbuffered, and sdram modules can be registered or unbuffered (the term unregistered is sometimes used too).

Q: Do I need registered memory?
A: That depends. If you want to use more than three double-sided modules, it is probably a good idea to use registered memory, because the "capacitive load" on the memory bus can get quite high, and you might experience stability problems. If you use three or less modules, usually registered memory isn't required, and you shouldn't buy it - it is more expensive and slower. Asus Germany recommends to use always registered modules if you use three or more ram modules in boards with the bx chipset. If you run a server however, you probably want to use registered modules - typically you will use all ram slots in those systems, and just for the possibility it might be more stable you might want to spend the extra cash and pay the (small) performance hit.
(Note: some boards with the bx chipset might not support registered memory correctly due to BIOS bugs / board layout, check your manual.)

Q: Can I mix registered memory with "normal" unbuffered memory?
A: No, you can't, the bx chipset doesn't allow that.

Q: Do I need ECC memory?
A: With ECC Dimms, memory errors can be detected (ECC = error checking and correction). The probablity for such errors is quite small, and unless you run a mission-critical machine (i.e. a server of some type), you typically have no reason to use ECC memory. These modules have 9 instead of 8 chips (or 18 instead of 16) and the module is organized as yzMx72 instead of yzMx64.
(Note: some boards with the bx chipset might not support ECC memory correctly due to BIOS bugs / board layout, check your manual.)

Q: Can I mix ECC and non-ECC memory?
A: Yes, you can. But it makes little sense, because the ECC feauture won't get used on the memory which is ECC capable.
You have to keep in mind too that often ECC memory is registered and your non-ECC memory probably not, so look for question "Can I mix registered memory with "normal" unbuffered memory?".

Q: Can I use DDR memory or even some old EDO modules?
A: No, you can't. DDR memory is not backwards compatible. And you most likely can't use EDO. The bx chipset indeed has support for EDO memory, but most boards don't (an exception to that are the bx based boards from supermicro). If you really happen to have a board which has support for EDO modules (check your manual) you can't mix EDO rams with PC66/100/133 sdrams, and you can only run at 66mhz FSB (that is, you'd have to use a P2 up to 333mhz or a Celeron up to 766mhz).

Q: What module sizes are supported on my bx-based board?
A: Generally, all modules smaller or equal to 64MB work without problems. No 512MB module will work in a board with the bx chipset, regardless what a vendor might tell you on the website. 128MB modules work as long as they have 8 or more chips (see here). 256MB modules might work, depending on the internal organization of these modules. You need modules with 16 ram chips, each chip organized as 16Mx8. The modules with 16 ram chips organized as 32Mx4 will NOT work, nor will the modules with 8 chips. More information here.

Q: What is the maximum amount of ram my board supports?

A: The bx chipset supports 1GB of ram. But because the largest dimm size supported is 256MB, it depends on the number of dimm slots of your board. See also questions "Do I need registered memory?" and "What module sizes are supported on my bx-based board?"

Q: How can I find out what type of Dimm I have in my computer?
A: Use ctspd, downloadable from http://www.heise.de/ct/ftp/ctspd.shtml - don't be afraid of the german website, the program is in english too.
Of special interest are the values under "extended display -> elementary module data". Here you can find the "number of banks (05)" (not to be confused with the "number of banks on each memory device (17)", this isn't that important) and the "module bank density". For a 256MB, 16 (or 18) chip dimm to work, these values must be 2 and 128MB, respectively.
Don't be afraid if ctspd shows "error" in the SPD-EEPROM complete and SPD-EEPROM bugfree fields, most generic ram manufacturers don't program the spd-eeprom correctly and the modules still work correctly in most cases (if you have branded ram modules, there are usually no errors).



Q: I've just bought some 256MB "high density" module with 16 chips on it and only half of the ram gets recognized. What's wrong?
A: If the modules was sold as "high density" then it is not compatible with boards based on the bx chipset. These modules use ram chips organized as 32Mx4 (see question "What module sizes are supported on my bx-based board?"). Note that the term "high density" is technically wrong, because these modules consist of ram chips with the exact same density (128mbit per chip) as those sold as "low density" (which usually consist of ram chips organized as 16Mx8). The term should be avoided because it will likely change its meaning over time too.

Q: My vendor lists a 128MB module as PC133, 16Mx64, will it work?
A: Sorry, but 16Mx64 is the EXTERNAL organization of the module and doesn't say anything about the internal organization. Newer 128MB modules might have only 4 chips organized as 16Mx16, and they will not work (at least not with their full capacity) on boards based on the bx chipset (since the bx chipset doesn't support 256 Mbit ram chips). All other 128MB modules which have 8 or more chips should work (since they are based on either 128 Mbit or 64 Mbit technology).

 Q: My vendor lists a 256MB module as PC133, 32Mx64, will it work?
A: Sorry, I have no idea. "32Mx64" refers to the EXTERNAL organization of the module, meaning it has 32 million addresses of 64 bit (=8 byte) each. Multiply 32 million with 8 and you get your ram size -> 256MB. This unfortunately means EVERY 256MB module (at least  168-pin Dimms) will be organized in this way, because the size is (obviously) fixed and the bus width (64bit) is given by the ram interface and thus fixed too. You need to know the INTERNAL organization of the module (the organization of the ram chips).

Q: I don't quite understand which 256MB modules will run. Can you explain a bit more on those 16Mx8 etc. terms?
A: I'll try. There exist at least four different types of 256MB modules.
(1). Modules with 16 ram chips, each chip organized as 16Mx8. The 16Mx8 means each ram chip has 16 million addresses and the data width of a ram chip is 8 bit. Since the ram interface calls for 64 bit data width, 8 chips are needed to form one ram bank. But because there are 16 modules on the dimm, this means there have to be two banks. The 16Mx8 also means one chips has a capacity of 128mbit. These are the modules which work on boards based on the bx chipset.
(2). 16 ram chips per module, each chip organized as 32Mx4. Because one chip has only a data width of 4 bits, all 16 chips are needed to form one ram bank. Such modules are cheaper to produce (because of the lower pin count of each ram chip), but they won't work in bx-based boards and will likely cause problems in any other chipset too, IMHO you really shouldn't buy them. They are mostly used in cheap generic ram (an exception are registered ram modules, where such chips seem to be quite common and where they shouldn't cause any problems in a board with a chipset which supports them - but unfortunately the bx does not).
(3). 8 ram chips per module, each chip organized as 32Mx8. Newer quality Dimms feature such organization, but they will not work on bx-based boards. Each chip has 256mbit and all 8 chip form one bank - to the chipset this looks almost the same as (2).
(4). Intel lists another type in their newer chipsets datasheets: 8 ram chips per module, each chip organized as 16Mx16. These modules consist of 2 banks, each bank has 4 chips. They aren't widely used in normal 168-pin dimms in reality yet but might be more popular in the future (they have 4 chips per side), but are often found in so-dimms for notebooks (4 chips per side). Such modules won't work, they look quite similar from a chipset perspective to type (1), but they require the so-called "8k refresh" and the bx chipset only supports up to 4k refresh.
Expect more of the type (3) and probably (4) to show up in the future for sale. They will likely be cheaper than the type (1) , because they use fewer chips, and with newer process technologies (read: smaller structures) the ram chips itself shouldn't be a lot more expensive to manufacture.

Q: My 256MB module has 8 chips on each side of the module, so it is obviously double-sided?
A: Life would be simple if things would be that easy ;-). There seems to be a bit of confusion with the term "single-sided" versus "double-sided". Sometimes it is used to describe how the module looks like, then it certainly is true that a module with 8 chips on each side is double-sided. But usually the term double-sided refers to the logical organization of the ram chips (synonym as banks), not the physical placement of the chips. It is possible to have a one bank module with 8 chips on each side of the module (as is the case if it is a 256MB module with chips organized as 32Mx4) and vice versa (at least in theory, I've not seen a module with 2 banks and 8 chips on only one side - this would require chips organized as yzMx16, which would be more expensive to produce without any advantages).



Q: I have more than 512MB memory and the board seems to recognize all of it, but Windows acts strangely, telling me that I don't have enough ram or just doesn't start some applications. Is my ram or board defective?
A: If you're running any version of Windows 95, 98 or ME then this is a known OS bug. If you don't believe me, believe M$: http://support.microsoft.com/support/kb/articles/Q253/9/12.ASP
The suggested fix is to limit your file cache to not more than 512MB. Put into your system.ini:

[Vcache]
MaxFileCache=524288

You can use a smaller value if you like, depending on your usage of the computer it might actually improve performance.
Any version of Windows NT, 2000 and XP do not require this fix.

Q: My computer is a bit unstable and I suspect I have some bad ram, but the BIOS ram test doesn't find any errors. Is there a better method to test the ram?
A: The BIOS test is very basic and really not good as a test program. I suggest using memtest86 to test your ram, this program seems to catch almost all errors if you let it run all tests. You can get it here: http://www.memtest86.com .

  Q: I have a P2, more than 512MB memory which all gets recognized but my computer runs really slow. What's wrong?
A: The older P2 (up to and including the 333Mhz version), have a cacheable ram area of only 512MB, so not all of your ram will get cached. Because the OS doesn't use the cached ram first, you will get a tremendous performance penalty. There is no workaround for that, you have to upgrade your processor (or use only 512MB ram).

Q: Where can I find even more information about the bx chipset?
A: If your familiar with reading datasheets and know a bit about computer technology, I'd suggest looking at the intel documentation of the i440bx chipset: http://developer.intel.com/design/chipsets/440bx/
Note: Because the documentation is quite old, you won't find any information regarding the use of 256MB dimm modules using 128mbit ram chips.

Q: I have no idea what you are talking about in this FAQ, can't you just tell me if the ram I'm going to purchase will work?
A: Unfortunately I'm not a good fortune teller. But if you buy branded ram, some companies (e.g. Crucial) have "memory selectors" online, where you can enter your board name and it will tell you which modules will work (unfortunately the memory selectors might not always list all possible options, e.g. it's possible it will only suggest pc100 modules).

Q: What brand of ram do you recommend?
A: I do not recommend any specific brand. I would recommend however not to buy just the cheapest generic ram available. There are rumors floating around some ram chip manufacturers don't even test their chips (because of costs), leaving the testing to the manufacturer of the ram modules. Don't know if it is true, but in the end it might be you who tests the ram, and I don't think the trouble is worth the cost savings. Additionally, if you plan to buy 256MB modules, you might have no chance to find out if the ram chips are 32Mx4 or 16Mx8. If you buy branded ram, datasheets are usually available (apacer has datasheets, crucial has their memory selector, and so on). If you plan on buying 128MB PC133 modules, cheap modules shouldn't be a big problem - especially if you don't overclock your board, you actually underclock your ram, which might help to run those modules stable.


Disclaimer: The author of the page is not responsible for the correctness of the information on this page.
Any comments, suggestions to Roland Scheidegger


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