Dell Dimension Memory Upgrade
Notes
compiled by Robert Hancock
This page has some miscellaneous information on upgrading RAM in Dell
machines. First is some general info on what kind of memory you need, then some
troubleshooting tips, and then some system-specific info.
General upgrade information:
See the sections below for any specific information that may apply to
your system.
The main types of memory used today are SDRAM (Synchronous Dynamic RAM) and
RDRAM (RAMBUS Dynamic RAM). The only Dell Dimension machines using RDRAM are the
XPS B-series Pentium III machines, and the 8100 and 8200 Pentium 4 machines.
Some older systems (original Pentium and earlier) used older types of RAM, such
as EDO DRAM and FPM DRAM.
SDRAM and RDRAM are not compatible - you cannot use one in a
system/motherboard designed for the other.
SDRAM: For systems using (original) SDRAM, the terms
PC66, PC100, and PC133 refer to the maximum clock speed the memory supports. You
can view the type of memory your system uses by going to
support.dell.com, looking up the User's
Guide for your model, then looking in the technical specifications.
In general, you can use SDRAM rated faster than your system requires without
problems, but this provides no performance benefit. One possible exception is
the D-series with BIOS version before A09, see below for details.
There is now another type of SDRAM available, DDR SDRAM, currently being used
on the Dimension 4400 machines. It transfers data twice on every clock cycle,
and therefore has twice the theoretical bandwidth of original SDRAM. Unlike
original SDRAM, the speed ratings for DDR are based on the maximum memory
bandwidth in MB/sec - at present, the two speeds are PC1600 (rarely used) and
PC2100. (If one were to go by the same naming system as original SDRAM, these
might have been better called PC200 and PC266.) Regular SDRAM and DDR SDRAM are
not compatible - you can't use one in a motherboard designed for the other.
For each speed of SDRAM there are two subtypes: CL2 or CAS2, and CL3 or CAS3.
(Some DDR memory is also available in CAS2.5.) You really don't need to worry
about this, either speed will work. This basically refers to the number of clock
cycles the system waits for the memory information to be sent after it is
requested. However for most memory access this makes little difference, as it
only really affects the first transfer in a sequence of transfers, and only by 1
clock cycle (10 nanoseconds for PC100).
RDRAM: There are 3 speeds of Rambus memory: PC600,
PC700, and PC800 (PC700 is not used much anymore.) You can install any speed,
but the system's memory will all run at the lowest common speed supported by all
the modules. If you go into the BIOS setup, you should be able to see what speed
your memory is - PC800 will show up as 400, and apparently PC600 will show up as
266. On the 8100s, apparently this info is displayed by going into the setup,
moving the cursor to the System Memory line, and pressing Enter.
RDRAM uses a 16-bit memory bus whereas SDRAM uses a 64-bit memory bus.
Therefore you have to divide the speed number of RDRAM by 4 to get a rough
indication of the equivalent speed in SDRAM. Actually, it's usually slower than
that because of the higher latency of RDRAM.
RDRAM systems require all memory slots without a memory module in them be
filled with a "continuity RIMM" which serves to terminate the connector. You
take these out when you want to put in a RIMM in that slot. If you remove memory
you should put the continuity RIMM back in, or the system might not run
properly.
Pentium 4 systems with RDRAM use a dual-channel system where two RIMM modules
are accessed at the same time, to effectively double the maximum memory
bandwidth. Because of this, memory modules must be installed in matched pairs -
i.e. the modules in the 1st and 2nd slots must be the same, and the modules in
the 3rd and 4th slots must be the same. By "the same" I mean preferably the
exact same modules - you want the same size, speed, and number of chips on the
module. You can use diferent modules between each pair, however.
Pentium III systems with RDRAM do not use a dual-channel system, so you can
add modules individually.
RIMM modules are sometimes available in both 8- and 16-chip versions.
Basically the 16-chip modules have chips covering both sides while the 8-chip
has chips only on one side. For any given size of module, the 8-chip module will
be using higher-density memory chips. Theoretically the latency on an RDRAM bus
increases - and therefore performance decreases - when more devices are added,
and therefore 8-chip modules might be a bit faster. However, I don't know how
significant this may be in real life - I would say likely not very significant.
RAM and system resources:
Increasing the amount of RAM in your system will NOT increase the percentage
of available system resources (i.e. as displayed in the System control panel's
Performance tab) under Windows 9x and Me. If you are having problems with your
system acting strangely, crashing, etc. due to running out of resources, more
RAM will not help you. Windows NT, 2000 and XP do not have this problem because
of their different architecture. See
this page for more information on this topic.
ECC vs. non-ECC memory:
- See
this page on Crucial's FAQ for information on what ECC means and how to
tell which kind of RAM you have. Dell only ships ECC memory if it is requested
by the customer when the system is built, so if you don't know what ECC is,
it's probably safe to say you didn't request it when you ordered and therefore
don't have it.
- You can use either ECC or non-ECC memory in your system. However the ECC
function will only work if all the memory installed is ECC. ECC memory is
usually a bit more expensive.
How much RAM do you need?
- In general with Windows 9x, upgrading from 64MB to 128MB results in a
fairly significant improvement, going up to 256MB provides a bit of
improvement, and going over 256MB provides very little improvement unless you
use programs that use a large amount of RAM such as Photoshop. Note that
Windows NT, 2000 and XP tend to want memory than Windows 9x/Me in order to run
smoothly.
Windows 9x/Me and over 512MB of memory:
- You may have heard that Windows 9x and Me cannot take advantage of over
512MB of memory. This is not actually true. What is true is that if you
install more than 512MB of memory with these operating systems, you have to
change a setting in the system.ini file to limit the disk cache size to 512MB
to prevent "Out of Memory" error messages.
This
Microsoft knowledge base article describes this problem and the
workarounds (the disk cache size change is described under the first bullet
point under "Workaround". In this case, you would want to add the line
MaxFileCache=524288 to the vcache section of the system.ini file in the
Windows directory. This does not prevent Windows from otherwise taking
advantage of the RAM over 512MB, it just limits the disk cache size to 512MB
(and it's unlikely you need that big of a disk cache..)
- With even larger amounts of RAM (approaching 1GB), you may experience
system instability even with the above setting change. Basically, Windows
9x/Me were never designed to handle this amount of RAM -
see this knowledge base article, and
this one. If you want or need this much RAM, you should really be using
Windows 2000 or XP, which do not have such problems with large amounts of RAM.
Windows 98 and large amounts of memory:
- I have heard of a number of reports of system slowdowns from people
running Windows 98, at least the original version, who have put in over about
256MB of RAM. While I can't really say for sure that Windows 98 and large
amounts of RAM could cause this, it seems likely. This does not seem to happen
with Windows Me. As for Windows 95, it's probably even worse, and you really
should upgrade if you're still using it.
x4 SDRAM memory:
- Some memory modules (usually cheaper ones) use a x4
configuration. This is where there are only 4 data bits coming out of each
chip on the module instead of the usual 8 or 16 bits. This means that 16
memory chips will be required to make up the required 64 bits coming out of
the module. Note that because a module has 16 chips on it, it is NOT
necessarily x4, because it could be x8 and be double-sided (effectively two
modules in one). However, if a module has less than 16 chips on it, it cannot
be x4. These x4 modules are apparently NOT compatible with Intel chipsets,
which all Dell machines use. They only work on other chipsets like VIA's. If
you have a module with 16 chips on it, the only way to tell whether it is x4
is by checking the specs for it. Usually, x4 memory is found in the form of
cheaper or generic memory.
Where to buy memory:
- One good place to buy memory is Crucial
Technology, a division of Micron. Their site has an online memory selector
where you can select your model of system and it will tell you what kind of
memory will work. Their memory comes with a lifetime warranty, and their
prices are usually very competitive. By the way, if you want to get memory
from Crucial and support this site at the same time, you can use the link at
the top of the main FAQ page to get to their site, and I'll get some
commission from your purchase (it won't cost you any extra).
- Unfortunately Crucial does not carry Rambus DRAM (RDRAM) memory at
present, which some systems (like XPS B-series and 8100) need.
This page
lists the RIMMs that have been tested on the Intel D850GB motherboard like
that used in the 8100, and
this page has information on RIMMs supported by the Intel VC820
motherboard like that used in the B-series machines. It may help you to find
the RAM that you need.
- In general, I don't recommend buying RAM from Dell. Their prices are often
higher. You are not really gaining anything in terms of the warranty by
purchasing memory from Dell, as installing memory from other vendors will not
void the warranty on your system. In addition, I have heard a number of
complaints about Dell memory not working properly, but I don't have enough
reports to consider this a trend.
- Buying generic or "no-name" memory can be a gamble. Although almost all
modules use RAM chips from a major RAM manufacturer (Micron, Samsung, Infineon,
Hyundai, Mosel Vitalic, etc.), who knows who assembled the module? The quality
of the module's assembly and design is the main difference in quality between
good RAM and marginal RAM. In particular, the SPD EEPROM on the memory must
contain the correct information to describe the operating parameters of the
module. Some systems will tolerate memory with incorrect SPD information, but
Dell systems generally do not. Using poor-quality memory can cause some
strange problems, such as a failure to boot (which can sometimes be fixed by
removing other modules), not recognizing the new memory at all or only
partially, system crashes, and general instability.
Memory troubleshooting:
If you experience any of the following problems after adding RAM:
- The module is supposedly the correct spec for the machine and inserted
properly, but the BIOS does not see the added RAM. (A BIOS update may help
with this on some machines.)
- Windows locks up repeatedly.
- Windows 9x/Me produces blue-screen error messages randomly.
- In Windows NT, 2000 or XP, you get blue-screen STOP error messages (often
referencing an error code like IRQL_NOT_LESS_OR_EQUAL).
- The memory fails the Dell Diagnostics memory test. (Note that some
programs which test the memory from within Windows can sometimes produce false
error reports.)
then the most likely cause is that the module(s) you have installed are
defective or incompatible. In particular, Dell machines may refuse to operate on
some memory - particular cheaper/lower quality memory - that may work fine in
other machines. See the last point above under "Where to buy memory".
Note that Dell Diagnostics' RAM test cannot catch all defective/incompatible
RAM. I once installed some RAM which passed the diagnostics' RAM test fine, but
consistently caused Windows XP to throw STOP errors on bootup.
Some people have reported system slowdowns, but no crashing, after installing
more memory. This could be due to one of their programs (including background
programs) or device drivers not running well with that amount of RAM (updating
them could fix this), or it could be a manifestation of the conjectured Windows
98 problem described above.
Dimension 4100 machines:
- Like all systems based on the Intel 815 chipset, these machines are
hardware limited to 512MB of RAM. There is no known way around this. (Intel
did this because their agreement with Rambus did not allow them to use a non-RDRAM
memory system on their highest-performing motherboards. The limit of 512MB RAM
was one of the main ways they removed that distinction from the 815-based
boards.)
XPS B-series machines:
- Apparently some people have had problems when mixing
RDRAM modules of different speed ratings (i.e. one PC600 and one PC800) on
these machines. This does not seem to happen in every case, but there have
been multiple reports of problems like this, so it seems that mixing memory
speeds is something to be avoided on these machines.
Lxxxr and Lxxxcx-series:
- Although these systems are capable of using
processors with a 133 MHz system bus, they will run the memory bus at a
maximum of 100 MHz, so there is no performance benefit to using PC133 memory
in these machines.
R-Series:
- Although Dell's information does not list 256MB DIMMs as supported in
these machines, Intel's information for the SE440BX motherboard these machines
are based on does indicate that these machines support 256MB DIMMs, and they
have been verified to work. You can see Intel's recommended memory
configuration info for these boards
here.
- PC133 memory does work. Some people have found that the BIOS displays a
message saying "SPD EEPROM data missing or inconclusive, do you want to
attempt to boot at 100 MHz bus speed?" or something similar. If you enter Yes,
it will boot up without asking from then on. It appears that the BIOS may not
be able to interpret the SPD information on some PC133 memory properly. Most
likely, those who get this message have modules whose SPD information is not
quite correct and the BIOS doesn't like it.
D-series:
- Versions of the BIOS for these machines prior to A09
do not recognize PC100 memory, as well as some PC66 memory properly. If you
plan to upgrade your system's memory using PC100 memory or experience any
other problems with the system failing to recognize installed RAM, I strongly
recommend updating the BIOS to version A09.
Dell Pentium (I) systems:
- Many Dell Pentium/Pentium MMX systems (not Pentium Pro or Pentium II/III)
that use SDRAM memory require 2-clock SDRAM. Check your system's
specifications' memory section on support.dell.com to see if your machine is
one of them. Regular PC66, PC100, etc. memory will NOT work in these machines
- if you use it, most likely only part of the added memory will be recognized.
One place (in fact, the only place I know of) where you can get 2-clock SDRAM
is Crucial, just select your system model
in the online memory selector. Because of low demand, you will pay quite a bit
more per megabyte than for more modern types of RAM.
- As well, systems using the Intel 430VX, 430FX, and 430TX chipsets (see
your system specs to determine which chipset your machine uses), if upgraded
above 64MB of RAM, could slow down, because these chipsets cannot cache more
than 64MB of memory, so any memory above 64MB will not be cached. This means
access to the memory above 64MB will be slower - and apparently Windows uses
the memory from the top down, making the problem worse. This is a hardware
limitation, it cannot be fixed by upgrading the operating system or BIOS.
Whether this will actually slow down the machine depends on the software in
use and the amount of RAM needed (i.e. whether the speed increase from
avoiding swapping to disk overcomes the slowdown due to the slower RAM
access). Linux users can partially get around this problem by making the
memory above 64MB a RAM disk and using it as swap space -
see here.