IBM 5160 and 3270 PC bring-up

hardware / status: active

After Byte Hamr I wanted an IBM to poke at the same way. I use my machines. There’s no nostalgia in it and these aren’t museum pieces. After a few months of looking I ended up with two: an IBM 5160 in a 5150 case and an IBM 5271, the 3270 PC, with an Intel Inboard 386 in it. Both came out of Tektronix and had been in storage since the 1990s, and as far as anyone knows had not been booted in decades. This page covers getting both of them to boot DOS from their hard drives. I didn’t keep a calendar during the work, so the log dates after the pickup are approximate and I put them on weekends.

Current state

As of 2026-09-10: Both machines boot from floppy and from their ST-251 hard drives, running DOS 5. The 5160 runs an EGA card in CGA mode on the IBM 5153. The 5271 runs a VGA card with the Inboard 386 active. The Inboard works in the sense that DOS loads and runs on it. I know there’s a DOS program for the Inboard and I still need to experiment to understand what it can do. The 5271 prints ERROR at boot with no code, and boots fine after. Both Model F keyboards are refurbished and in daily use. The 3270 side of the 5271 is untouched. I’m running it as a plain XT.

Architecture

Two XT-class machines. The 5160 has a NEC V20 on a 256-640K board. The 5271 has a stock 8088 on a 64-256K board plus the Inboard 386 in a slot, which takes over the CPU function. Each has its own MFM controller card driving a Seagate ST-251. Video is an EGA card in CGA mode on the 5160 and VGA on the 5271.

Hardware

IBM 5160: 5150 badge and cover, 5160 internals, motherboard revision B1N22, NEC V20, no 8087. Tandon TM100-2 full-height 5.25 inch floppy. A half-height 3.5 inch drive came with it and is pulled and untested. One I/O card I haven’t identified yet. IBM 130 W PSU with a new RIFA cap and a new large ceramic cap.

IBM 5271: 64-256K motherboard, Intel 8088, Intel Inboard 386/PC. Tandon TM100-2 full-height 5.25 inch floppy. Seagate ST-251 on a Western Digital WD1002A-WX1. VGA card. IBM 130 W PSU, inspected, original caps.

Shared: IBM 5153 CGA monitor, two IBM Model F 83-key XT keyboards, one 122-key 3270 keyboard, four ST-251 40 MB MFM drives of which two work, a few 8-bit EGA cards (BCCA, Paradise Basic EGA, Everex EV-657), and the 3270 cards that came with the 5271: the IBM 6320984 display adapter and what I think is the host connect card.

Tools: a DMM and a Siglent SDS1204X-E scope.

Gateware and firmware

Decisions

2026-03-01 (roughly): passed on the eBay builder and went local. Dan, a collector a few hours south, said what he had and was willing to make a deal.
2026-07-18: took as much of it as I could.
2026-07-25 (roughly): didn’t power the 5160 until the PSU was inspected. The RIFA had cracks in it, so it and the big ceramic got replaced first.
2026-08-08 (roughly): an EGA card in CGA mode for the 5160, because that’s the combination that finally worked with the 5153.
2026-08-23 (roughly): low-level format from the WD Super BIOS formatter at G=C800:5 in dynamic mode, because the ST-251 has 820 cylinders and the card’s fixed drive table stops at 663. Tried SpeedStor, went with DEBUG.
2026-08-23 (roughly): interleave 5:1 first, then 3:1.
2026-08-29 (roughly): 3270 mode is a later project. Running the 5271 as an XT for now.

Open problems

The 5271 says ERROR at boot with no code. It boots anyway.
Inboard 386: find and run the DOS utility for it, see what it can actually do.
The 3270 keyboard controller card (IBM 61X6609 or 1503893) is missing, so the 122-key keyboard and the 3270 display adapter do nothing yet, and the display adapter needs a 5151 or 5272 monitor I don’t have.
Two of the four ST-251s are dead.
The floppy alignment was done with a hand-assembled loop in DEBUG and the scope. I wrote a spec for a DOS tool that holds a track, checks the recorded cylinder with the FDC Read ID command, and sweeps every track for read reliability. Unbuilt, planned.
Identify the I/O card in the 5160.
An 8087 for the 5160.