Not sure I ever saw any, but even if they do, they won't help you 😮

The HP D530 has an Intel 865G chipset. As its datasheet indicates:

The memory bank address lines and the address lines allow the GMCH to support 64-bit wide x8 and x16 DIMMs using 128-Mb, 256-Mb, and 512-Mb SDRAM technology.

Max 512Mb (=64MB) per chip and max 16 chips on an unbuffered DIMM means max 64x16=1024MB per DIMM. Even if you were to find DDR1-SDRAM DIMMs with 2GB in 16 1024Mb chips, it would only be detected/addressed as 1GB per DIMM.

So you're limited to 2GB total in this machine.

Even if you could find unicorn 2GB unbuffered DIMMs, Windows XP can't address the entire 4 GB of RAM due to system devices and the video card eating into the address space, the video card being the biggest offender.

You'd generally end up with anywhere between 3.25-3.5 GB of usable system memory, and much less if the video card has a lot of onboard memory.

Okay, good deal. Just didn't want to leave anything on the table for this system. Would still love to come across some of that ram for giggles now that I know it is uncommon, even if it isn't for this.

They exist, but are pretty pointless. The i865/i875 were Intel's last pure DDR1 chipsets, and both supported max 512Mb chip densities, so max 1GB unbuffered DIMMs. AMD's So939 Athlon64 CPUs were the last AMD DDR1 memory controllers and also did max 512Mb, so max 1GB.

The only chipsets I can find that support DDR1 in 1Gb memory density and so 2GB DIMMs are the later 9xx series Intel chipsets, which also supported DDR2. Even there, they only seem to support 1Gb density at lower clock speeds. You'd almost always be better off getting a cheap, easily sourced 2GB DDR2 DIMM.

If you want to find a module, look for Samsung M368L5623MTN-CB3, a PC2700 DDR1 2GB DIMM.

I distinctively remember 2GB DDR1 dimms have been for sale years and years ago. They became available when DDR2 was already a thing, were stupidly expensive and only worked on some machines, I'm not sure they were even PC-3200 I believe they were slower.

There was no point to them at that time as I remember buying 2 of them (dual channel) would have been more expensive than buying 2x2GB DDR2, an AM2 Motherboard and an athlon 64X2.

Customer grade memory ended at 1 Gb. Everything higher is buffered workstation/server memory, usually with ECC.