Can I have a CP/M Console?

Everything about Andy Key's great Emulator MEMU
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Crazyboss
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Re: Can I have a CP/M Console?

Post by Crazyboss » 20 Oct 2015 20:46

config ?

dont you mean reconfig?
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Dave
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Re: Can I have a CP/M Console?

Post by Dave » 20 Oct 2015 21:01

If we had meant RECONFIG, we would have said so :-)

config for native MTX

reconfig for REMEMOrizer etc.

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Re: Can I have a CP/M Console?

Post by Crazyboss » 25 May 2018 10:39

I used fullcpm.bat to mount two type 07 floppy images, that works ok, but it seems like its not possible to mount a SD image as the second floppydrive?

It refuse to let me config C:18

Looking at the diffirent Memotech Disk types. It seems to be quite stupid to have a 40 track 3.5" - As I know all 3.5" drives have always been 80 tracks, double sided or single sided. The MSX e.g had a 3.5" disk format single sided. 360kb and also used 3.5" double sided 720kb (which is DOS compatible).

I think 5.25 drives could be 40 and 80 tracks, I also saw at least one diskdrive which was 96 tracks? maybe it was something special?

The MSX uses 512 bytes per sector and 9 sectors per track. both for the 360/720kb format. It seems to be stable, I still have MSX diskettes which is read without any errors. The Amiga used 11 sectors per track, gives around 880kb on a diskette, I have alot of problems reading those diskettes now.

By the way, people said if you downgrade a HD diskette (1.44 Floppy) to a DD diskette by covering the HD hole. Its still not good, I never had problems, but some people around the retro computers forums said it will not keep the data as secure as a true DD diskette.

I am not sure if the SDX could be hacked to read and write 1.44 floppys, but I remember a quite Clever MSX guy tried to make the MSX do it back then, he said the CPU was not fast enought to do it. MSX used Z80 clocked at 3.57mhz, I think he got something to work using a Z80B at 6mhz. But its 25 years ago now :(
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Dave
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Re: Can I have a CP/M Console?

Post by Dave » 25 May 2018 11:37

Are you using MEMU?

If so, the above ("config for native MTX reconfig for REMEMOrizer etc.") is relevant.

MEMU is an MTX/SDX/FDX emulator - it does not emulate REMEMOrizer, so uses the standard CONFIG program. The FDX/SDX and hence config.com don't know anything about type 18 "disks" (SD cards).

I don't think you will have seen a 96 track disk, you probably mean 96 TPI (Tracks per inch), it's a measure of the disk track spacing, i.e, 80 tracks will be in 80/96ths of an inch. The heads travel something less than an inch to cover 80 tracks.

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Re: Can I have a CP/M Console?

Post by Dave » 25 May 2018 11:42

From my website . . . . .

There are potential problems with the choice of media when using HD drives with DD floppy disks.
A look at a typical floppy disk head should help show what the issues are.
The picture shows a floppy disk head arrangement from a 3.5" drive.
The Read/Write head is followed by a "Tunnel Erase" head on either side of it to clean up the track and ensure there is good separation between adjacent tracks.
Photo from Gough's Tech Zone (see it here : http://primrosebank.net/computers/mtx/t ... altfdd.htm

Problems can occur because a 96 TPI (80 Track HD) drive has narrower heads than a 48 TPI (40 Track DD) drive. If you write data onto a blank DD disk using a HD drive, a DD drive should be able to read the disk - the data track will be narrower than had it been written on a DD drive, but it should be read OK.
However, if you write the same data from an HD drive onto a disk previously formatted on a DD drive, you are likely to get problems as the new, narrower, data track will be on top of the old, wider, track. The data can probably still be read on a HD drive, but problems will likely occur when trying to read the data on a DD drive. The HD Tunnel Erase heads will not have cleared out the old data from the wider track and the DD heads will likely read a mixture of the new, thinner, track data and the older, wider, track data. This could be a problem if you intend to use the disk in both HD and DD drives.

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Re: Can I have a CP/M Console?

Post by Bill B » 26 May 2018 08:58

If I remember correctly, Andy made the format of SD cards the same as that used for Silicon Disks. In which case you should be able to mount an image in MEMU using "-sidisc-file n file". You will need to load the SIDISC driver in MEMU. You should then be able to read the image.

What Dave is describing above is the issues concerned with mixing 40 track and 80 track disks. However both IBM 720K (DD) and 1.4M (HD) disks are 80 track. The difference is that HD disks have 18 sectors per track, while DD disks have only 9 sectors (https://en.wikipedia.org/wiki/List_of_f ... sk_formats). This means that the bits on a HD disk are more closely packed. I believe that, in order to make this work reliably, they had to change the magnetic properties of the media on the disk. As a result, the head of a DD drive is not always able to reliably change the state of the bits on the HD disk.

As a side note, with the right software, the MTX 3.5 inch SDX drive is able to read and write IBM 720K formatted disks. I use this to move data between my MTX and PC.

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Re: Can I have a CP/M Console?

Post by Dave » 26 May 2018 09:44

From the same page on my website . . . .

“A word about 3.5" disk media.

High Density (HD) 3.5" media is not the same as Double Density (DD) media - their characteristics are similar, but are NOT the same. This is why the HD drive has an additional hole in the diskette, opposite the write protect hole, this allows the drive to identify which media type is in the drive and adjust its write configuration accordingly. Whilst formatting a DS/DD disk to HD was possible (if an additional hole was punched in the disk), the format would often result in bad sectors, particularly towards the centre of the disk where the data density is highest- it was pretty obvious that you were taking a risk with your data. On the other hand, if you wanted to use an HD diskette to create DD diskettes, putting opaque tape over the density select hole will fool the drive into thinking that a DD disk had been inserted and will write to the disk at DD density, apparently with no problems.

When you do this though, you are writing to media of one type (HD) with a write current appropriate for lower density (DD) media. Most of the time, you will not notice any problems, but this technique is not as inherently reliable as using the correct media type. For important data, it is better to use DD media for DD formats - the slight problem being that 3.5" DS/DD media is pretty hard, if not impossible to find these days!”

And on this page http://www.primrosebank.net/computers/m ... _media.htm

Media Type

The Oersted (Oe) is a measure of magnetic field strength and is used to describe the magnetic properties of floppy disk media and its coercivity - a measure of the resistance of a ferromagnetic material to becoming magnetized/demagnetized. Whilst 3.5" Double Density (DD) and High Density (HD) have very similar magnetic properties, DD media has a coercivity of about 660 Oe and HD media is about 720 Oe.

The coating on a DS diskette is about 1.9 microns thick, while on an HD diskette, it is about 0.9 microns thick.

What this means in practice is that when a HD drive sees an HD diskette, it knows to write data using a higher current than if it were a DD disk. If you cover the hole in an HD diskette to trick the drive into thinking that a DD disk has been inserted, it will write data at a current level compatible with DD disks, i.e., LESS than is required to securely write to HD media. While the disk may appear to be fine, it is highly likely to lose data very quickly.

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Re: Can I have a CP/M Console?

Post by 1024MAK » 26 May 2018 20:18

Crazyboss wrote:Looking at the diffirent Memotech Disk types. It seems to be quite stupid to have a 40 track 3.5" - As I know all 3.5" drives have always been 80 tracks, double sided or single sided. The MSX e.g had a 3.5" disk format single sided. 360kb and also used 3.5" double sided 720kb (which is DOS compatible).
No, when they were first developed, there were some 40 track single sided 3.5" floppy drives. The Opus Discovery disk drive system for the ZX Spectrum used such drives (link). But fairly soon, they were replaced by 80 track single sided 3.5" floppy drives (Atari 520 STFM computers came with this type). These were normally double density types. Then double sided drives. High Density (HD) drives followed.
Crazyboss wrote:I think 5.25 drives could be 40 and 80 tracks, I also saw at least one diskdrive which was 96 tracks? maybe it was something special?
Some drives could actually exceed 80 tracks, both 5.25" and 3.5". How many depended on the actual drive mechanism itself. But I don't think there were ever any with 96 tracks. I think you are misremembering the number, as it was the tracks per inch figure (TPI), not the total number of tracks used.
Crazyboss wrote:The MSX uses 512 bytes per sector and 9 sectors per track. both for the 360/720kb format. It seems to be stable, I still have MSX diskettes which is read without any errors. The Amiga used 11 sectors per track, gives around 880kb on a diskette, I have alot of problems reading those diskettes now.
Reliability of a disk with a greater number of sectors than normal very much depends on the disk drive being able to spin the disk at the same rate as the drive that formatted the disk. Too much of a difference in speed will result in the controller accessing the wrong part of the disk surface. If it is a write operation, it's likely that the existing data will be corrupted.
Crazyboss wrote:By the way, people said if you downgrade a HD diskette (1.44 Floppy) to a DD diskette by covering the HD hole. Its still not good, I never had problems, but some people around the retro computers forums said it will not keep the data as secure as a true DD diskette.
This practice is not recommended (as explained by Dave). Especially with pre-formatted disks (e.g. 'IBM' formatted). The disk can become unreadable within days/weeks. However, there have been reports that if you completely erase the whole disk with a disk erasure tool (a box with a strong magnetic field) or use a (rare) unformatted disk, it's more reliable.
Crazyboss wrote:I am not sure if the SDX could be hacked to read and write 1.44 floppys, but I remember a quite Clever MSX guy tried to make the MSX do it back then, he said the CPU was not fast enought to do it. MSX used Z80 clocked at 3.57mhz, I think he got something to work using a Z80B at 6mhz. But its 25 years ago now :(
Some older computers can be modified to read/write HD disks. The thing to remember is that the data rate for a HD disk is double that of a DD disk. Some Atari ST/STF/STFM/STE computers can be modified (I've done one of mine). In general, it's the floppy disk controller (FDC) system that needs to be modified. Some 8 bit CPUs however may not have the memory bandwidth to keep up.

Mark

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Re: Can I have a CP/M Console?

Post by Crazyboss » 29 May 2018 10:20

I have mostly used 3.5" diskettes at the MSX platform and PC back then.

We replaced 3.5 drives with HD drives cause even back then it was hard to get DD drives. I never had problems reading or writing DD disks.

What I always did when i got a new box of diskettes back then, I formated the disks and then i put it away for a week or so. Then I used a test program to test for read and write errors. If I could hear the head travel to try to read the sector again, i put the diskette in the bin.

After using this way i didn not have any errors at all, I guess most of the diskettes from the 90s can still be read today :)

Also i used to buy 3M diskettes back then.

Other stupid people tried to hack DD diskettes into HD diskettes by drilling the extra hole :) I assume it will not last for very long.
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Re: Can I have a CP/M Console?

Post by AndyKey » 28 Oct 2018 13:49

Just spotted this
I used fullcpm.bat to mount two type 07 floppy images, that works ok, but it seems like its not possible to mount a SD image as the second floppydrive?
It refuse to let me config C:18
You could load the SD Card image into Silicon Disc, and then access that.
The largest Silicon Disc type code (4F) just happens to have exactly the same disk geometry as SD Card.
Well, actually it's no accident, as both aspire to be the largest you can actually support on CP/M.

memu .... - sidisc-file 0 mysdcard.bin ....

CONFIG F:4F


There was also a comment about CONFIG v RECONFIG.
Technically, RECONFIG is a superset of CONFIG, and so can also be used on earlier SDX/FDXs
And it also reuses (rather than wastes) high memory when reconfiguring drives of the same size, so its generally a better version to use.
{{{ Andy

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