IBM 5100 Internal Tape and the 5106 External Tape Unit



Before discussing the IBM 5100 tape unit, I want to clarify how not every 5100/5110 can support a tape unit. And a tape unit generally cannot be added to those units that don’t have one.

To begin, the IBM 5100/5110 are categorized into two main types: Type 1 (has internal tape unit) and Type 2 (no internal tape unit).

Only the Type 1 has the circuitry components on the Base IO card to add an external IBM 5106 tape unit.

The Type 2 models were slightly lighter, since the internal tape mechanism uses a bulky motor and fan.

Why offer a Type 2 models if you can’t save any of your programming? These models were used mainly as terminals to connect to other systems (and would interact with data on those systems, rather than saving anything locally). Additional expansion cards were necessary to conduct these connections.

For the IBM 5110, the IBM 5114 disk drive unit could be added to either type. A summary of the expansion options is as follows:

By convention, there are “A” models (APL), “B” models (BASIC), and “C” models have both. So, a “B12” would be a BASIC model Type 1 with 2-filled memory banks (16×2 = 32KB). All variations were made (APL-only, BASIC-only, and some that did contain both). This type of designator (e.g. “B12”) was generally only on the sales receipt of the system, not on the system case itself.

Below is the IBM 5110 Processor and corresponding Base IO card from a Type 1 model. These are typically combined when mounted in the A1 board using two “cross-patch” connectors (that facilitate a few additional pin connections between the boards, beyond what the A1 board itself provides).

Below is a comparison of the IBM 5110 Type 2 vs Type 1 Base IO card. There are many small differences, but primarily the difference is in the bottom left corner. With no support for the internal tape unit, the Type 2 model also has no support for the external tape unit.

The IBM 5106 External Tape Unit

The 5106 (external tape) has a control board, and QIC tape mechanism, that is identical to what is used in the internal tape unit. But the back portion of the 5106 has the Auxiliary Tape Adapter Card that communicates with the main IBM 5100 unit. For the system to be able to determine where the set of added peripherals ends, a “terminator” connector is needed on the last device in the sequence.

The IBM 5100/5110 uses QIC (Quarter Inch Cartridge) form factor tapes, which support being digitally Fast Forward and Rewind by the computer system (so there is no Play, Record, FFWD, RWD, buttons as typically found on audio cassette decks). The higher “DC” (Data Cartridge) number generally corresponds to the length of the tape material, and thus more capacity (but without a reduction in reliability, as you tend to see with audio cassette tape).

More photos of the IBM 5106 tape unit with the top cover off. This unit has not been cleaned, but still works perfectly.

The 5110 SLM (System Logic Manual) provides a clue as to why a 5106 external tape unit might not work across both the 5100 and 5110: per the logic diagram, a different auxiliary tape adapter card is needed to adjust the “Osc/4” signal (some cards are equipped with a jumper to easily make this adjustment). See bottom right corner in the diagram below (5110 vs 5100 logic paths).

The Internal Tape Unit

Photos of the Internal Tape unit (which the 5106 uses this same set of hardware, except for the front fan components).

Notes on the Tape Head

Measurements related to the tape head pins.

NOTE: The above “ohm” values were measured on a tape head that wasn’t working, so I can’t vouch that these are the correct/expected/typical values. But the presence of continuity between pins should be correct.

NOVEMBER 26, 2022

Successfully transplanted the external tape unit in the IBM 5106 over into the IBM 5110.

The IBM 5110 tape unit has a small fan near its drive belt mechanism. The IBM 5100 and IBM 5106 do not have this small fan, but this “non-fan” version is still compatible with the IBM 5110..

The IBM 5110 has two sets of mounting holes, to accommodate both the “with fan” and “without fan” versions of the QIC tape unit.

I had hoped the IBM 5106 itself would be compatible with both the IBM 5100 and IBM 5110. While technically it is, turns out some jumper setting adjustments are needed on the Tape Adapter Card of the IBM 5106 (to make it work with the IBM 5110). The 5106 I obtained did not have these jumpers available. Despite this, I’ve verified you can unbolt the entire tape unit in the 5106 and placed it into an IBM 5110 Type 1 (i.e. if it already has the wiring for a tape unit and the Base IO card that supports tape operations).

Some additional notes:

  • BASIC programs saved on the IBM 5110 end up with file type 11 (as opposed to file type 4 on the IBM 5100)
  • On the 5110, I was able to issue the command “MARK 64,9999,1” (64KBx9999 files). Specifying five digits for number of files (10,000 or higher) beeped as an invalid input; the spec can hold more files, but the MARK command seems to cap it to 9999 max. This means the MIM 3-30 spec of 16KB files seems to be incorrect (the diagram states 3FFF max file size), and the file count is limited to 9999.
  • The 620ft DC6150 tape seems to hold about 432KB of file data (maybe 450KB, but not over 480KB). This can be one large file (e.g. “MARK 400,1,1“), or many smaller files (e.g. “MARK 16,27,1“). It takes about 3 minutes to format either of these.
  • REWIND and UTIL (dir) of 64KB took about 24 seconds for each file, implying a read speed of about 2,730 bytes per second. That’s consistent with the IBM GIM (General Information Manual) for the IBM 5110, which has the following:

Where else were QIC Tapes used?

In an advertisement in PC Magazine 1983-10 (page 24), a company called Tallgrass provided an external QIC-based backup system (for IBM PC, T.I. and Victor 9000 computers).

Prices of 3M QIC tapes from 1983:

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