View Full Version : IBM Diagnostics

March 6th, 2005, 04:07 AM
Can anybody point me to a source for a version later than v2.
V2 insists that my floppies are 320K.

March 6th, 2005, 04:59 AM
Can you expand on that? 320K might not be bad.

The original PC diskette drive was single sided with 40 tracks, 8 sectors per track. That worked out to a capacity of 160K.

A very quick upgrade made the drives double sided, so now the formatted capacity was 320K.

Maybe at the same time (or very shortly after) the format changed to 9 sectors per track instead of 8. It was the same hardware, but they squeezed in another sector. That brought the capacity to either 180K or 360K, depending on if you were single or double sided.

So there really is no difference between 320K and 360K, other than a software difference. The drives are identical. Therefore, having diags report 320K shouldn't be too upsetting.


March 6th, 2005, 05:37 AM
Thanx for the response.
Your point about "not too upsetting" is valid.
It's just a desire for the software and hardware to complement each other.

March 6th, 2005, 04:30 PM
It would be nice if the software matched exactly, but it's possible that it won't. Using my line of reasoning, the software has to check for either 1 160K format or a 320K format to tell if it is a single sided or double sided drive. 180K or 360K would have been nicer, but remember that DOS 1.1 only used 160K, and the diagnostics probably uses the lowest common denominator.

I need to run Diagnostics on my PC and see what it does - it would be interesting if it does it on all machines. If not, maybe there is a strangeness on your machine.

March 7th, 2005, 02:35 AM
Careful with the tag STRANGE! Just cos our water goes down the bath in reverse, it don't mean our 5150's work in reverse :))
Seriously tho your ref to DOS 1.1 got me searching and I think you hit it on the head. Formatting gives the option of 8 sectors which is to maintain compatibility with DOS 1, and my Diags Disk is Formatted 160K, so it's only gonna see 320 aint it?
The Command.com on this Diag is Sept 82.
The XT BIOS was Oct 82. Did the XT intro the 180/360K Format?

joe sixpack
March 7th, 2005, 06:22 AM
i had to read this a few times to understand what is going on here, im still a little lost.
are you looking for dos or is your system only reporting you have 320k?

There is a driver you can load but im not sure when it was added to dos
i think 4.0 it's called "DRIVPARM" or something cloes to that it will override
what the system tells dos the drive is... or so i've read i've never had to use it.

i would think the system would'nt put up to much of a hissy fit thinking
your drive is 320k over 360k but then again.

If you need a diagnostics disk i have one at my website i think it worked
on a number of ibm systems but im unsure it if works on the 5150 so
use at your own risk:!:. however it is a 360k image. it works for my 5170 AT

there is less then 250k of files on the disk so you should be able to
get a program to convert it OR you might be able to chop off the excess
with a hex editor (the ass end of it is all free space) however the fat table
will be wrong. meaning it would be fine if the disk is write protected because
no data files exist in the missing data but writing would prob cause problems.

btw im pretty sure the xt did have some of the first 360k drives i think.

Terry Yager
March 7th, 2005, 07:11 AM
i had to read this a few times to understand what is going on here, im still a little lost.

It's that walking around upside-down all day...makes the blood rush to the head, don'cha know.


March 7th, 2005, 07:41 AM
Aussie? Hadn't noticed. For me strange usually refers to Europe. :-)

The change to 9 sectors per track instead of 8 predates the XT - it happened on the PC. I'm not sure when the change occured, or what caused it - it could have been a DOS update or a BIOS revision. Either way, all of the diskette drives could do 9 sectors per track - it was just a software change.

Rarer would be to find an IBM PC with a single sided drive. That would be amazing. The XT came out around 1983. The change to double sided drives occured in 1981 or early 1982. I've never seen a single sided PC diskette drive.

If DIAGS is checking the format of the existing disk to determine the drive capacity I would be very suprised. DIAGS would have to be shipped on a single sided 160K diskette to be compatible with every variation of the PC, unless they dropped support for the very earliest diskette drives. (Generally IBM doesn't drop support for anything that a customer might be using.) Boot a normal DOS diskette (2.x or better), then do a chkdsk on the diags disk to see what capacity it is:

-if it is 160K, then Diags is not looking at it's own disk to determine your drive time. (Assuming Diags is reporting 320k ...)
-if it is 320K, then Diags might be looking at it.

It would be more reliable if Diags probed the diskette controller. I would imagine that a single sided drive would reject a format request that was for both sides, and thus Diags could tell if it was a single sided or double sided drive. But that requires a test format.

Like I said - I need to fire up my machine and see how it behaves. Unfortunately my normal every-day use machine is a PCjr, which always has double sided drives. I can run the diskette based Diags on a PCJr, but it gets really upset during some of the tests. :-)

Terry Yager
March 7th, 2005, 07:50 AM
The switch to 9 SPT was a DOS revision. I just don't remember if it was version 1.1 or 2.0.


joe sixpack
March 7th, 2005, 04:15 PM
The XT came out around 1983. The change to double sided drives occured in 1981 or early 1982
i was guessing as my source QUE upgrading & repairing computers 8th edition
said the 5150 was released in 82 and the very first models had only 16kb ram,
they quickly jumped to 64kb the later models shipped with up to 256kb

i guesstimate that double sided drives came around about 82 just as you said
so i figured the 5150 was one of the first computers to have it.

for some reason i can not find a detailed history of floppy disks & drives
everytime i search i end up with a page that is very short or a page about
the history of dos.

if anyone knows of a site covering 8"inch -> ls-120 please share

March 7th, 2005, 04:25 PM
I like the QUE book, but they are definitely wrong on the year of the 5150. The 5150 (the original IBM PC) was released in 1981.

I have an early 5150 with just 64K on the motherboard. The first 16K is soldered, and the other 48K is socketed. This machine is so old that it doesn't count the memory visibly during the BIOS POST, and it won't recognize memory past 544K. (That was an early BIOS bug.) This BIOS also doesn't scan for BIOS ROM extensions like those found on EGA, VGA, and hard disk controller cards. But as old as this BIOS revision is, it is still not the oldest.

Finding a 5150 with the original BIOS revision in it would be incredible ..

March 7th, 2005, 04:42 PM
Joe: Thanx 4 the link mate. I've dl'd it. I'm going to test on my spare XT Board. I figure it'd be a valid testbed. If it shits itself..Too bad, so sad.
I know that could be considered sacrilege by some, but "to me" it aint a true XT cos it's got the NEC V20 chip.
Even my True 5160, with the Intel chip, has been relegated to being the 5150's spare parts unit.
Again, thanx heaps.
Terry: Blood rush to the head is a bit weird at first, but it ensures a Bloody good supply of oxygen to the brain.
mbb...: Europe strange. Why?

Cheers Guys

March 7th, 2005, 05:42 PM
Europe and strange? One word - France. :-)

Anyway, I pulled the 5150 out and tried diagnostics 2.05. It did not report the capacity of the diskette drive. First it reported that I had two diskette drives, which it could determine from the dip switch settings on the motherboard. Then, as I suspected, during the diskette drive test it figured out that I had 2 double sided diskette drives.

What part of diagnostics reported that you had a 320K drive?


March 7th, 2005, 06:51 PM
mbb.. System Unit Test 500 writes to a Scratch Disk (pre-formatted 360K), then asks for verification of 320K Floppy.
If I respond NO, it reports a Test Error.

March 7th, 2005, 08:24 PM
And exactly what version of Diags is this? I used version 2.05. During the diskette test it told me single sided or double sided, nothing else.

March 7th, 2005, 09:56 PM
The Start Screen verbatim:

The IBM Personal Computer DIAGNOSTICS
Version 2.00 (C)Copyright IBM Corp 1981, 1982




Aside from the Floppy size, the routine returns absolutely accurate info!
It's Installed Devices listing is precisely what is in the system!
I know it's genuine IBM, cos if I use my Yamaha CGA card it has a Hissy and aborts and fails the Video Test. Whereas the IBM CGA card is fully tested and Passed!
As a note of interest: The Format is F#*king useless. It creates a disk that CHKDSK returns as Invalid Media.

March 8th, 2005, 06:06 AM
Ah, 2.00 vs. 2.05. Mine has a copyright date that is from 1981 to 1983. I think that's the difference .. the later version is better in that it doesn't inaccurately report the diskette capacity - it just says double or single sided.

BTW, 2.05 has the same formatting bug. The diskette is unusable.

Can you do me a favor? I'd like a diskette image of your 2.00 version for the collection. There is a wonderful utility called "ditu" that you can find here:


It's a diskette imager - makes raw dumps to a file.

Run chkdsk first to see if it is a 160K or 180K format. The options are:

ditu 0:40:1:8 <filename> for a 160k diskette
ditu 0:40:1:9 <filename> for a 180k diskette
ditu 0:40:2:8 <filename> for a 320k diskette
ditu 0:40:2:9 <filename> for a 360k diskette

The utility also handles 720k and 1.44MB formats, and anything else you can create with DOS.

Send me the file (mbbrutman at yahoo.com), and I'll try it here. If you want 2.05, give me an email addr ..


March 8th, 2005, 05:36 PM
As a note of interest: The Format is F#*king useless. It creates a disk that CHKDSK returns as Invalid Media.

That sounds familiar. IIRC, SCANDISK will fix that. (A single byte wrong, media descriptor I think)

March 11th, 2005, 05:50 PM
Ah, what a hoot.

Rolf sent me a diskette image of his Diagnostics v2.0. I ran it on my 386 clone, which has a real double sided double density drive, just like a PC. Sure enough, it asked me if it was a 320K drive.

I'd have run it on the PC, but I think the 386 clone did the job. Diagnostics v2.0 is definitely old stuff, probably predating the change from 8 sectors per track to 9 sectors per track. So for it, 320K is the sign of a double sided diskette drive.

Case closed.