AMD

AMD Phenom II X 2 3.5 GHz Dual-Core 521 Processor, HDX521OCK23GM, SOCKET AM3

Bottom line: The AMD Phenom II X 2 3.5 GHz Dual-Core 521 Processor is a specs-and-price decision rather than a crowd-consensus one in the retro cpus category. Check the specification table below against one or two close alternatives — on price and spec fit, not on star ratings.

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By Mike Perry, Founder & Editor-in-Chief · Listing data updated 2026-09-25

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 →

Before you buy

Confirm socket / form-factor / power-rating compatibility against your build before ordering
Used and vintage listings vary by seller and condition — check the listing photos, description and return terms before buying

Manufacturer description

AMD Part Number: HDX521OCK23GM. AMD PHENOM II X 2 DUAL CORE 521 PROCESSOR. Socket:AM2+ / AM3 65 WATTS. 3.5 GHz,20 00 MHz Hyper Transport Link. To protect the pins, the processor will be placed in a. Note: The last five digits of the serial number of each processor.

SpecPicks Verdict

SpecPicks scored AMD Phenom II X 2 3.5 GHz Dual-Core 521 Processor using a rating × review-volume × price-fit model applied to published specs and reviews across the retro cpus category. AMD's retro cpus 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 retro cpus 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.

Full Specifications

cores	2
tdp_w	65
part_number	HDX521OCK23GM
clock_speed_ghz	3.5

Ready to buy?

AMD Phenom II X 2 3.5 GHz Dual-Core 521 Processor, HDX521OCK23GM, SOCKET AM3 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. SpecPicks earns a small commission on qualifying purchases — thank you for supporting independent review work.

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