VOGONS


First post, by Paddan1000

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There seem to be sticks of RAM around where the memory bus is halved to 4 bits instead of the regular 8 bits. The ones with less bits are called High Density RAM and are slower and inferior to the ones with more bits called Low Density RAM.

I went through my collection of SDRAM and fortunately didn't find any HD-RAM, but a couple of sticks had a memory bus of 16 bits. Are these some kind of Ultra Low Density RAM and what kind of performance gain can I expect from using them? I plan to put them in a Pentium III 500 MHz or an Imac G3 400 MHz.

If I were to use HD RAM of the worst kind, how would that affect performance in real world tasks?

Finally all of my SDRAM-sticks are either CL2 or CL3, whatever that means. Is there any benefit to use only the CL2 ones?

The perfect stick of SDRAM would be a PC-133, 512 MB with a 16 bit memory bus and CL2. Do that type of DIMM exist and is it readily available and affordable?

Reply 1 of 7, by noshutdown

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i am not very clear about what you are talking about, but aren't all 168pin sdram dimms 64bits wide? most common tsop sdram chips are 16bit wide each, so a dimm needs at least 4 tsop chips to form a bus 64bits wide, although most dimms have 8(single side dimm) or 16(double side) chips to provide a larger ram size.

and when you say density i guess its about ram size. most sdram chips are 128mbits, 256mbits or 512mbits each, and the dimm size is chip size times 8 or 16. the larger ram size a chip has, the harder to overclock.

Reply 2 of 7, by schaap

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Noshutdown has explained things perfectly AFIAK. All DIMMS are 64 bits wide, only the width of the ram chips varies. Some DIMMS have one side, others have two, each side of a DIMM is controlled separately by the memory controller as a 64 bit wide "bank" of memory.
AFIAK the width of the RAM chips has no influence on the speed of the memory, because they are all controlled in parallel.

Sometimes DIMMS with 32MB per (side/)bank or smaller are referred to as "low density" because these work with the earliest implementations of SDRAM (Intel 430VX, etc.).

CAS latency is explained on wikipedia: http://en.wikipedia.org/wiki/Cas_latency

CAS latency has some influence, depending on the application you might see a small performance increase from using CL 2 memory. In my experience you won't notice anything in your G3 iMac, in your Pentium III you might get a 1 or 2% performance increase on memory bandwidth heavy applications.

When you mix CL 2 and CL 3 DIMMs the highest CAS latency will be used (CL 3).

Reply 3 of 7, by fronzel

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Imho it doesn't make any difference at speed, at least nothing i could witness. Anyways, some older laptops can only use "low density" RAM, i remeber i had some old Sharp notebook in Japan that would gladly accept 128 MB "Low density" RAM but was absolutely unable to accept High density ones. So i guess that's the most important difference.

Reply 4 of 7, by Paddan1000

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I'm referring to what's written here, among other places:

http://reviews.ebay.com/Myth-Low-Density-vs-H … 000000001236178

It mentions that High Density SDRAM is much slower than Low Density RAM.

I assume they mean that it's the halved bus width (4 bits) of the individual chips of High Density RAM that makes them slower. By logic that would make chips with a double bus width (16 bits) faster.

Reply 5 of 7, by noshutdown

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Paddan1000 wrote:
I'm referring to what's written here, among other places: […]
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I'm referring to what's written here, among other places:

http://reviews.ebay.com/Myth-Low-Density-vs-H … 000000001236178

It mentions that High Density SDRAM is much slower than Low Density RAM.

I assume they mean that it's the halved bus width (4 bits) of the individual chips of High Density RAM that makes them slower. By logic that would make chips with a double bus width (16 bits) faster.

okay his words seems reasonable, but its only about some uncommon, poorly built dimm sticks, which totally violate the pc memory standards. i guess they wouldn't boot a rig at all if the mainboard is strict with memory standards, and you shouldn't run into any if you are looking at dimm sticks of mainstream brands.

Reply 6 of 7, by Paddan1000

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Here is another post that explains the difference between high- and low density RAM.
http://reviews.ebay.com/High-or-Low-density-D … 000000002086216

I found I had a pair of 256MB modules of SDRAM that were only detected as 128MB by my Pentium III, although they were detected as 256MB by the Imac G3. The brand was "V-data", which is a sub-brand of A-data. It was this kind of module:
http://www.memoryc.com/computermemory/sdram/1 … vdatapc133.html

They are single sided, unlike my other 256MB modules that are all double sided, and I suppose they are examples of this dreaded High Density RAM. Apparently not even sticking to known brands will keep me safe.

I could benchmark them and compare them to Low Density RAM to solve this question of Low Density RAM superiority once and for all, but then I need a good (and free) RAM benchmarking program that works on a PowerPC with OS X Tiger, since the Imac G3 is the only computer I own that will accept these V-data sticks. Any suggestions?

Reply 7 of 7, by Paddan1000

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Perhaps I was to quick in judging the V-data RAM. The motherboard of my Pentium 3 has a i440BX chipset and according to point number 3 in the quote below there are some types of quality RAM that it won't recognize properly. I suppose it's because the chips are of the same kind found on Low Density double sided 512 MB RAM sticks. Accordning to the manual, the motherboard only accepts 256 MB sticks at the most and then perhaps it will reject 256 MB sticks built with chips meant for 512 MB sticks.

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. The […]
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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.