Adaptec ACB-4000 Winchester Disk Controller ST-506 ST-412 ISA 1-to-1 Interleave

Adaptec ACB-4000 Winchester Disk Controller ST-506 ST-412 ISA 1-to-1 Interleave

The Adaptec ACB-4000 is a vintage ISA-bus hard disk controller card designed to interface ST-506/ST-412 type Winchester drives with IBM PC/XT/AT compatible systems. It supports both 5.25" and 3.5" Winchester drives and features 1-to-1 interleaving, which eliminates the sector-skip delay common on slower controllers of the era and allows the drive to operate at full speed on a single rotation pass. Assembly number ASSY400006-03.

Specifications & What's Included

• Manufacturer: Adaptec, Inc.
• Model: ACB-4000
• Assembly Number: ASSY400006-03
• Bus Interface: ISA (8-bit)
• Supported Drive Interface: ST-506 / ST-412 (Winchester)
• Compatible Drive Form Factors: 5.25" and 3.5" Winchester hard drives
• Interleave: 1-to-1 (full-speed sequential sector access)
• Main Controller ASIC: Adaptec A4C010 (custom Adaptec IC, x2 on board)
• Secondary Module: Adaptec HD/SD 8316D
• Support Logic: 74LS-series TTL ICs (e.g. 74LS373N visible)
• Edge Connector: ISA card-edge (8-bit slot compatible)
• Card only — no cables or mounting hardware included

Applications

The ACB-4000 was designed for use in IBM PC, PC/XT, and PC/AT class computers and compatible systems during the mid-to-late 1980s, when ST-506 and ST-412 were the dominant hard drive interfaces for personal computers. ST-506/ST-412 controllers like the ACB-4000 connected the host system to the drive's read/write electronics via separate data and control cables, with the controller handling encoding, decoding, and sector management on the card itself. The 1-to-1 interleaving capability made the ACB-4000 a high-performance choice in its era, since most competing controllers required 2:1 or 3:1 interleave to compensate for slow CPU interrupt response — meaning they had to wait one or two disk rotations between consecutive sector reads. Adaptec's implementation allowed back-to-back sector access with no rotation penalty, significantly improving disk throughput. Today these cards are sought by vintage PC collectors, retrocomputing enthusiasts, and those maintaining legacy IBM-compatible systems that rely on ST-506/ST-412 hard drives.