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, 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:

How much RAM do you need?

Windows 9x/Me and over 512MB of memory:

Windows 98 and large amounts of memory:

x4 SDRAM memory:

Where to buy memory:

Memory troubleshooting:

If you experience any of the following problems after adding RAM:

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:

XPS B-series machines:

Lxxxr and Lxxxcx-series:



Dell Pentium (I) systems:

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