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The Thunderbird architecture is an overclocking paradise for those with a motherboard that supports multiplier configuration. The Athlon remains an unlocked processor, though AMD has tried to lock its Socket A chips. Most of today's Thunderbird processors ship with no multiplier locking mechanism, while many of the earlier models require a modest amount of work to bypass the AMD locking technique.
Unlocking Thunderbird chips of the Socket A variety requires reconnecting a series of trace routes along the topside of the processor substrate. These tiny bridge connections were severed by a laser, which locked the multiplier. Luckily, AMD has stopped making such cuts because the company feared increasing processor failure rates due to the heat and stress associated with the lasercutting process.
Reconnecting the L1 trace routes is a relatively minor operation. The routes must be connected using a conductive transfer medium. Some vendors, such as HighspeedPC.com, offer a specialized adhesive tape with tiny metal strips already embedded at the required connection points. This may offer the simplest solution.
Another quick fix is simply to redraw the bridge connections with a regular number-2 pencil. Each point of the circuit must be connected to the point directly across from it, creating a series of parallel lines. Lead pencils should be avoided. A standard wooden pencil with a finely sharpened tip works best. Sharpen the lead with sandpaper first to insure accuracy. Some hardcore enthusiasts may opt to use a silver-fluid compound instead, but be warned this often creates a permanent connection. The pencil trick is preferred because the marks can easily be erased if something goes wrong during the unlocking procedure.
Each of the L1 circuit pathways must be connected using a straight-line approach. Take great care to ensure that each pencil mark connects the intended circuit points with no overlapping of any lines. An overlapped line can cause a short circuit and consequent unusual results or even processor failure. Examine each pencil line, once it is drawn, under a magnifying glass.
Successful pencil modification allows unrestricted multiplier manipulation. Partial or no success is common on the first try. A less-than-perfect redrawing usually results in allowable multiplier manipulation in the .5 to 1x range. Erasing and redrawing the lines can fix such problems.
Once unlocked, the Thunderbird offers standard multiplier options from 5 to 12.5x, in .5x increments. Some motherboards allow 13x and possibly 13.5 to 14x multipliers, though these cause problems for most Thunderbird models. AMD does produce a 14x Thunderbird, but the multiplier is configured internally through the regular autodetection routine.
The Athlon Thunderbird fares much better for processor-to-chipset bus overclocking compared to its older Slot 1 K7 sibling. Most early Socket A chipsets can successfully reach the 115 to 120 MHz range (230 to 240 DDR). The latest generation offers scalability to 166 MHz and beyond. Most manufacturers now equip their Athlon motherboards with active chipset cooling, as thermal regulation is necessary to maintain stability when overclocking.
Another excellent way to maximize performance of 100-MHz Thunderbird models is to lower the internal multiplier, and then raise the processor bus to 133 MHz. The Athlon is a bandwidth-intensive design that can benefit from processor bus overclocking. All the latest chipsets from ALI, SIS, and VIA allow 133-MHz processor bus support.
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