wrote:
This computer (Compaq 5400US) came with two 128M Ram sticks, for a total
of 256m. The computer maximum allowed RAM is 512M. I want to upgrade
to that maximum. There are only 2 slots. I can install TWO 256m
sticks. But can I install just ONE 512m stick?

Finding memory for this machine is a challenge in itself. It needs
168pin - Low density - PC133 SDRAM. Trying to locate using charts
provided by the memory companies all show ONLY up to 256m, and they want
$20 or more per stick. I'm planning to build a more powerful computer,
but this old relic runs, and seems to work well. So, for now it will
do.

But I'm not sticking $40 or more into it. However, I have found on ebay
some used RAM, buy it now, Two 512m sticks of 168pin - Low density -
PC133 SDRAM, for about $10 incl. shipping. Although I can only use one
of them, the price is right, and I'll have a spare.

But I'm not 100% sure if I can use just one 512m sticks, or MUST I use
TWO 256m sticks?



I answered your question in a previous posting.

815E chipset (which is an 815 with an ICH2 Southbridge)
has an artificial limitation of 512MB. Intel did that for
market differentiation, so the 815 was intended for "value"
platforms. This is different than VIA Technology of the day,
who did not mind it if a value computer supported 1.5GB total.

Suggested RAM (select speed as per what worked before)

512MB module - 16 chips (ones with 8 chips, might not exist)
256MB module - 8 chips or 16 chips total

Due to the 512MB "total" limit of 815 Northbridge, you can use

1x512MB (16 chips on the DIMM) - contents of other slot ignored

or you can use

2x256MB (8 chip or 16 chip PC133 should be OK per DIMM)

With the 512MB DIMM, you'd be leaving a slot blank.

(PDF page 11)
http://download.intel.com/design/chi...s/29835102.pdf

Integrated SDRAM Controller

* 32 MB to 512 MB using 16-Mb/64-Mb/128-Mb/256-Mb technology

Page 140 shows usage of 32Mx8 chips is supported (which is a 256-Mb chip).
Sixteen chips at 32Mx8 is a 512MB DIMM. Which is the largest supported.

The only thing "anomalous" about that chipset, is the
invention of an artificial limit. It's a four bank (two slot)
design, and so it should have supported a grand total of
1024MB as 2x512MB DIMMs. But due to the Northbridge capping
memory decodes at 512MB, then under certain conditions (1x512MB),
the other slot becomes effectively useless. If you stuck
512MB + 128MB in the board, it still reports 512MB in the BIOS.
It's like the other stick isn't even there.

Paul