Micron

Crucial 4GB Kit (2GBx2) DDR2 800MHz (PC2-6400) CL6 Unbuffered UDIMM 240-Pin Desktop Memory

Name: Crucial 4GB Kit (2GBx2) DDR2 800MHz (PC2-6400) CL6 Unbuffered UDIMM 240-Pin Desktop Memory CT2KIT25664AA800 / CT2CP25664AA800
Brand: Micron
SKU: B0011A4UZE
Price: 37.99 USD
Availability: InStock

Bottom line: The Crucial 4GB Kit ($37.99 on Amazon as of 2026-10-06): Matched 2GB x 2 kit, no mismatched-stick gambling; main trade-off: 4GB total caps out many 32-bit era builds anyway.

$37.99

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🛒 See live eBay price Also on Amazon — $37.99 Compare to similar memory & ram

By Mike Perry, Founder & Editor-in-Chief · Listing data updated 2026-10-06

Mike Perry — Hardware researcher since 2014. For retro PC hardware and period-correct parts, synthesises manufacturer documentation, community compatibility lists and marketplace listings rather than first-hand lab testing. Core beat: GPU performance across gaming, rendering, and local-LLM inference. About the author →

*Price sourced from Amazon.com. Last updated 2026-10-06. Price and availability subject to change.

Pros & Cons

Pros

✓ Matched 2GB x 2 kit, no mismatched-stick gambling
✓ Full PC2-6400 800MHz speed with CL6 latency
✓ Unbuffered non-ECC, fits standard consumer DDR2 boards
✓ Micron-made and 100% tested before shipping

Cons

✗ 4GB total caps out many 32-bit era builds anyway
✗ CL6 is looser than CL5 DDR2 kits of the same era
✗ DDR2 only, will not fit DDR3 or DDR much newer boards
✗ 240-pin desktop UDIMM, no laptop SO-DIMM option

Manufacturer description

The Crucial 4GB DDR2 kit (CT2KIT25664AA800) is a two-module 2GB x 2 set built for the 240-pin DDR2 desktop platforms that defined the mid-2000s, and it remains one of the most-reviewed retro memory upgrades you can still buy new. Each module runs at up to 800MHz (PC2-6400) with CL6 latency, unbuffered and non-ECC, so it drops straight into any consumer board that takes standard DDR2 UDIMMs without the registered-memory compatibility headaches that trip up server-pull RAM. Micron builds and 100% tests these modules, and the kit is sold interchangeably as CT2CP25664AA800, so either part number…

SpecPicks Verdict

SpecPicks scored Crucial 4GB Kit (2GBx2) DDR2 800MHz (PC2-6400) CL6 Unbuffered UDIMM… using a rating × review-volume × price-fit model applied to published specs and reviews across the memory & ram category. Micron's memory & ram lineup sits within the broader category mid-tier; price and specs are the deciding factors over brand loyalty here. Judge it on the specification table and the price rather than on sentiment: check the figures that decide your use case, then put it side-by-side with two or three close alternatives in the Compare tool before clicking through.

Common buyer scenarios for memory & ram of this kind: matching it to an existing build, replacing a failing part, or upgrading from a previous-generation equivalent. Check the spec table below against your current setup — particularly socket / form-factor / power-rating fields — and confirm compatibility on the retailer's listing before purchase. Prices and stock are set by the retailer and may have moved since this page was last updated.

Frequently Asked Questions

Will this DDR2 kit work in my motherboard?

It fits any desktop board that accepts 240-pin DDR2 UDIMM memory, unbuffered and non-ECC. It will not work in DDR, DDR3, or laptop SO-DIMM slots. Check your motherboard manual for DDR2 UDIMM support before ordering.

What is the difference between CT2KIT25664AA800 and CT2CP25664AA800?

Nothing functionally. Crucial lists CT2CP25664AA800 as identical to CT2KIT25664AA800, so either part number delivers the same 4GB (2GB x 2) DDR2 800MHz CL6 pair.

Do both sticks have to be installed together?

No, but installing both in the matched channel slots is the point of buying a kit. Two identical 2GB modules let compatible boards run dual-channel instead of single-channel.

Will my system actually see all 4GB?

A 64-bit operating system will. A 32-bit version of Windows XP or Vista typically reports around 3.2GB regardless of how much is installed, which is a limitation of the OS, not this memory.

Is this new memory or pulled from used systems?

These are Micron-built modules that are 100% tested before shipping, not salvaged pulls. For current warranty terms, check the product listing at the time of purchase.

Key Features

Increases system performance
Easy to install
Premium quality memory from a trusted brand
100% Tested
Identical To: CT2CP25664AA800

Full Specifications

Brand	Micron
Voltage	1.8 Volts
RAM Size	4 GB
Model Name	Crucial
Unit Count	2.0 Count
Form Factor	DIMM 240-pin
Identical To	CT2CP25664AA800
Memory Speed	800 MHz
Model Number	CT2KIT25664AA800
Number of Pins	240
Mfr Part Number	CT2KIT25664AA800
Memory Generation	DDR2
Compatible Devices	Desktop
Data Transfer Rate	800 MHz
Memory Form Factor	UDIMM
Additional Features	Lightweight
Computer Memory Size	4 GB
Warranty Description	Limited lifetime warranty
RAM Memory Technology	DDR2
Column Address Strobe Latency	6
Full listing title	Crucial 4GB Kit (2GBx2) DDR2 800MHz (PC2-6400) CL6 Unbuffered UDIMM 240-Pin Desktop Memory CT2KIT25664AA800 / CT2CP25664AA800

Ready to buy?

Crucial 4GB Kit (2GBx2) DDR2 800MHz (PC2-6400) CL6 Unbuffered UDIMM 240-Pin Desktop Memory CT2KIT25664AA800 / CT2CP25664AA800 is vintage hardware; the used and vintage market on eBay carries most of the live inventory. Prices and condition vary by seller and move in real time, so we link the live listing rather than quote a cached price. It also has an Amazon listing — check it for current price and availability. SpecPicks earns a small commission on qualifying purchases — thank you for supporting independent review work.

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*Price sourced from Amazon.com. Last updated 2026-10-06. Price and availability subject to change.