Peter Seibold Finds a New Use for the Vintage AGP Slot, Doubling the Throughput of a Retro-Style NAS
While AGP graphics cards are few and far between these days, the slot can live a second life for 66MHz PCI or PCI-X boards.
Vintage computing enthusiast Peter Seibold has found a new use for the Accelerated Graphics Port (AGP) found on PC motherboards of a certain vintage — thanks to an adapter that converts it to a high-performance 66MHz Peripheral Component Interconnect (PCI) port instead.
"The major bottleneck of the Super Socket 7 platform is the shared bandwidth of the PCI bus," Seibold explains of the reason for his unusual adapter, "with a theoretical maximum of 133MB/s but more like 60-90MB/s on this platform. There's no way I can get even close to gigabit line speed with my Socket 7 NAS [Network Attached Storage appliance] with the gigabit NIC and the SATA controller connected to the same bus."
For most, that would mean it's time to pick out new hardware — but for Seibold, whose motto is "building resource efficient systems from obsolete parts," there was an alternative: the AGP slot. Launched in 1997, the Accelerated Graphics Port (AGP) standard took the Peripheral Component Interconnect (PCI) bus and tweaked it for high-performance — by the standards of the era — graphics cards.
While a NAS doesn't really need a high-performance graphics card, the AGP slot does provide what is effectively a second and entirely independent PCI bus — and one which can transfer data considerably faster. "With my prototype of an AGP to PCI adapter," Seibold explains, "we can actually use it for something else [other] than the graphics card."
Using the AGP slot instead of the contentious PCI bus, Seibold is able to sustain a transfer rate from the NAS of more than 200MB/s — over twice the rate achievable using PCI devices alone. The only catch: standard 33MHz PCI cards aren't compatible with the AGP slot. 66MHz PCI, and PCI-X cards, though, work fine, Seibold found.
Seibold is selling compact adapter boards, based on the spaghetti-wired prototype, on his website for €9.90 PCB-only, €29 with a PCI connector, or €39 as a fully-assembled unit ready-to-go.