Computer Components

Why the motherboard decides which RAM you can buy:

its slots are cut for one memory generation. DDR4 and DDR5 sticks carry the notch in a different place, so a DDR5 kit will not go into a DDR4 board however hard you press, and a recent AMD AM5 or Intel Core Ultra build takes DDR5 only. Laptops use the shorter SO-DIMM sticks, and many thin laptops have their memory soldered on, so check for a free slot first. Two matching sticks run in dual channel and beat one stick of the same total, which is why a kit sold as a pair is worth more than two loose ones. A new kit also runs at a base speed until XMP or EXPO is switched on in the BIOS, the usual reason someone decides a fast kit is slow.

Turning an ex-office desktop into a gaming PC:

is where many people start, and it decides which graphics card and power supply will fit. Office machines such as a Dell OptiPlex, an HP ProDesk or a Lenovo ThinkCentre use their own power connectors and board shapes, so their parts rarely move into a standard case and standard parts rarely go into them. The small-form-factor versions take only low-profile cards powered through the slot. A tower with a standard board opens the field, but a bigger graphics card usually means a new power supply too, and that is the part not to economise on: a branded unit with an 80 Plus rating, because a cheap one that fails can take the rest of the PC with it. Complete machines are listed under desktops, and the SSD that makes an old one feel quick under storage and hard drives.

Memory prices against the electricity bill:

a single 16 GB stick of DDR4 runs around ₡70,000 new and a 32 GB DDR5 kit goes past ₡250,000. Memory has no moving parts and almost never wears out, so a used kit that passes a full memory test is worth close to new; the discount pays for the buyer’s risk, not for wear. Graphics cards work the other way. An old flagship such as a GTX 1080 Ti plays games about as well as an entry RTX 4060 while drawing roughly twice the power, and in a household already past 200 kWh a month, where each extra kWh costs about half as much again, a few hours of play a night adds something like ₡15,000 to ₡20,000 a year. Take that off the saving before settling on the bigger, older card.

Server memory sold as desktop RAM:

catches second-hand buyers more often than any other part, because registered ECC sticks pulled from servers are cheap, plentiful and look identical in a photo. RDIMM, Registered or ECC on the label means it will not boot an ordinary desktop board, so ask for a clear photo of every sticker. Sticks mixed from different kits can work, but they are a common reason a PC will not hold its rated speed. On a graphics card, play something demanding for a long session and listen: a rattling fan, or a card that slows as it warms, points to dried thermal paste or worn bearings. Be wary of the unbranded power supply thrown into a gaming bundle. Processors rarely fail, but a photo of the socket shows whether anyone has bent the pins.

Proving a stick of RAM works before the buyer arrives:

means testing before you list, because memory cannot be judged by looking at it. Run a full memory test, keep a screenshot of the pass, and photograph each label with the part number readable. Put the generation, capacity and rated speed in the title rather than just “RAM for PC”, and for a graphics card say which PC it came out of and why. Someone coming out to Moravia or Naranjo for a pair of sticks will want to see them seated in your machine with the BIOS reading the full capacity and speed, then watch them go into an anti-static bag rather than a shirt pocket.