Is DOS 6.3.5 suitable for a system with 640K RAM, and an 8088?

I managed to get my system reading the disk, after meticulously trying different jumper configurations for the disk controller card, but it now tells me there is no boot history. I’m guessing this means that the disk either doesn’t have DOS installed on it, or it is corrupted in some way. I’ve decided the next step is to purchase a copy of DOS and hope for the best. But I’m unsure if an 8088 is adequate to run the version I found.
The system also has a Zilog Z80 as its coprocessor, so I’m assuming that maybe it has adequate processing power, and it definitely has adequate RAM. I’d like to know for sure if it will work before I purchase it, or if maybe there is a better version of DOS someone would recommend for this system. Thank you for any advice you can give on this matter.

I don’t know the answer - I might wonder if FreeDOS or some other re-written DOS is suitable for an 8088 PC.

It’s an interesting question as to how this machine makes use of the two CPUs - which one boots up? How is the other one ever made use of?

For reference, here’s your previous thread:
Removing an old motherboard. DTK 39784 PiM Turbo

At least, I assume this is the same machine?

Is that the Z80 you mention?

It is, yes. I’m not 100% on how to identify these older chips, tbh. I assumed since the 8088 is identified with a set of four numbers that most if not all chips are.

It looks something like this chip, and maybe it is an 84C4, and my dyscalculia was acting up.:upside_down_face:

Ah, right, that’s an I/O controller interface chip, a dual-channel UART, from the Z80 family, but not a Z80 cpu.

I see. I’m really not sure which chip it is now, so I’ll investigate when I get home in a couple of days. Once I’ve actually identified the chip, maybe we can figure out if this version of DOS is appropriate for the system. Tho, from what I read it seems like it’s meant to control the CMOS or something like that, and the board it’s on actually does have a button cell CMOS battery.

I don’t know if DOS 6.3.5 will run; I’m not even sure what DOS that is! (PC-DOS? DR-DOS? MS-DOS only ran to 6.2.2 before jumping to 7.)

The DOS that would have been “correct” for that machine at the time it was purchased was probably MS-DOS 2.0 (most likely 2.02, 2.0 was very short-lived), and most of them were probably running 3.3 by the end of their lives. You need at least 2.0 for hard disk (and subdirectory) support. I strongly suspect that up through 5.0 will run on it, and maybe beyond.

I would probably try to find a copy of DOS 3.3, if I were you; I think that’s probably the best tradeoff for capability vs. memory consumption for that PC.

Whether the hard disk works or not or has DOS installed or not is probably hard to tell at this point. It’s probably an MFM drive with an MFM drive controller (two cables going from the controller to the hard drive?), and those are not self-identifying. The drive has what is called “geometry”; the number of cylinders, heads, and sectors associated with the physical drive. Some drive controllers are fixed geometry (they can only control one type of disk) and some are multi-geometry. If yours was already paired with the disk that you have, it presumably can drive that disk; some of those jumpers you have been moving may control that geometry, and they will have to be set accordingly. (Basically, you not only have to get the controller talking to the computer, you also have to get it talking to the disk!)

Once you have almost anything running on it, getting more stuff running on it is relatively easy; however, you’ll almost certainly have to be able to write 360 kB 5.25" floppies to get started. If you have another computer with a 5.25" disk drive, most drives can write 360 kB floppies without trouble; you can probably even format one from Windows, although you won’t be able to install DOS 3.3 on it. If you don’t, you’ll want to either buy working 5.25" boot floppies or get someone to write one for you; ideally, if you have someone write one for you, you’ll also have them write a copy of some serial communication program as well (assuming you have a serial port!), so that you can transfer additional software from a newer computer without third-party assistance.

As @EdS mentioned, FreeDOS does run on XT-class machines, although whether it will run on your machine or not is a bit of a question (it depends on the quality of the BIOS clone). Anyone with a 5.25" drive should be able to boot FreeDOS and write you a 360 kB boot floppy. FreeDOS probably isn’t an idea long-term OS, though, as it’s quite large compared to DOS 2 or 3 (and you don’t have either a lot of RAM or a lot of drive space on one of those old machines!). It does have the advantage of being free and not requiring a license, however!

It’s a version of IBM PC-DOS.
Anyway, I found a 5.25" floppy version of 3.30A, and have two 5.25" Floppy drives in the PC. 3.30A will work on this machine?

Looking at it further, I’m guessing it probably should, as the copyright dates match up with when the parts were made, and it has the DTK logo on the disks. I’m guessing since it’s a DTK motherboard, having the DTK logo on the disks should be a good sign.

It’s probably the ideal version of DOS for that machine, in fact.

Excellent, it may in fact end up costing me less as well. Thank you both so much for your time and assistance.


As far as I know most versions of DOS run in real mode which is the only mode the 8088 has so that should be fine. Some of the fancy multi-tasking DOSes might use protected mode but that could be simulated. I imagine the only issue with using newer DOS versions on an 8088 is speed.

Even the fanciest, newest, “slowest” DOS is much faster than the disks that it operates, on an 8088. The biggest problem is that even an extra kB or two of RAM usage for the OS can be a big deal when you’re limited to 640 kB total. The older DOS kernels were smaller.

Yeah, that’s what I was worried about. I did end up winning that copy of 3.30A, so I should have a suitable version for it now.