How to mount more than 2 HDISK immages?

[Semper Talis]

My system is able to mount 2 HDSK images on A: and B:.

In the default settings I see there is a platter 0 and a platter 1 available.

So I mounted two more images by using switch A10 to select Unit 2

When I then boot the Hard disk boot rom, I get drive A: and B:

but c: gives me a "Bdos Err On C: Bad Sector"

The image I use is fine and if I mount it on Unit 1 platter 1 it works fine.

Here a screenshot of the Hard disk mounts 

Note that I have played with the "NUM_HDSK_UNITS" setting set to 4 instead of 2

But the problem is the same with the setting to 2 .

With setting at 4 I hoped that then the c: and d: would be populated with Unit1 platter 2 + 3 but this did also not happen.

Is there any setting in the config files I have to change in the source code to get Unit1 and Unit 2 to mount?

Thanks for your help

[John Galt]

under Cp/M C: and D: are 2 360KB floppies. 

mount the 2 hard drives then you can mount 2 floppies. for C: and D:

Cp/m 2.2 only supports 2 hard drives and 2 floppy drives at a time.

[Semper Talis]

Oh, that's a bummer .

I personally had never original hardware which had CP/M drives , just floppy.

OK, that settles it .

Thanks for the info .

[John Galt]

its a little more complicated 

basically: the cp/m we have around today came from one of two versions that managed to survive as a backup.

one of the versions that survived was configured to have 4 floppy disks mounted and had an opening in the device configurations.

over the last 20 years many people modified and messed around with it and incorporated Mp/M functions.

they tricked CP/M by modifying sector sizes into seeing 2 of the floppies as hard drives either 5MB or 8MB in size. they played with the allowable file index sizes

you end up with a very usable O/S with a ton of features plus optimized modifications of disk access which greatly speed things up for file access.

all this is just for Cp/M 2.2 which was also the most widely used Cp/M 3 came right at the end and never gained any market share.

Cp/M 3 presents different issues and was never really modified as much as 2.2 was.

you will notice 8MB disk hiding in the Disk mounted files, while 5MB disk hiding in the hard drive mounted files.

the 5MB method of harddrive access works best while the 8MB harddrive causes some issues with configurations.

the best setup tends to be two 5MB hard drives and two 360KB Floppies.

there are many tools allowing for running compressed archives directly.

there are even more modifications for the 5MB images to add even more functionality.

Fred has some amazing options

https://github.com/ratboy666/hd1024

https://github.com/ratboy666/r

the Version provided on the SD card is a 255 limited file system so i recommend looking at Fred's HD 1024 disk, it also incorporates Mp/M user functions which can be used as a kind of file directories.

the provided version on the SD is

CP/M 2.2b v1.5
For MITS 88-HDSK

the newest version is (which is freds version)

CP/M 2.2b v1.6
For MITS 88-HDSK

---

R is an amazing utility similar to LRUN

this allows compressed binaries to run directly out of an archive as long as they are simple and do not need external overlays.

basically you can compress the entire Cp/M utilities into a single COMMAND.LBR file and save tons of space and also file name space to allow even more programs to occupy the disk.

i have 1000s of Cp/m utilities on my 5MB disk image with over 1MB of free space for anything else i could want.

it really opens your eyes to how amazing Cp/M could have been in the 1980s.

[John Galt]

I'm leaving tons of things out just to keep things simple.

https://deramp.com/downloads/

http://cpmarchives.classiccmp.org/

[Semper Talis]

Hi John,

thanks for sharing all this information .

It does show how much history is behind CP/M.

I was quite surprised when I used first time the hard disk ram and on c: and d: 300k floppies showed up .

I can live with the 2HD + 2 Floppy setup , as my programming is most likely not exceeding a 300k Floppy capacity :-) 

It was just something I was exploring and wondering why you can have 4 units with each 4 plates but can only mount maximal 2 plates overall :-) 

I bet that was a problem nobody ever had with the real hardware , at $12.000 per HD that would be quite a costly experiment in the 70/80's :-) 

My first HD was $1000 and had a wooping 30 MB.....more space than I ever would need for all mys software forever !!! Or so I thought back then to justify the cost.

Again thanks for sharing ! 

[John Galt]

I have assembly source code i wrote that exceeded 400K thanks to all my comments LOL! takes forever to compile at 2mhz

just thinking back to memory cost very few people in the early days had 64KB to play with.

if you had four 8" floppy drives you might have been a millionaire.

same my first hard drive was 10MB and cost around 1500$ i remember upgrading to either 25 or 35MB and thinking how i would fill 3 times the space, which i did almost instantly.

you work with the limitations and find ways to bend the rules like the Cp/M hackers before us did. either way you have a really fun time.

don't forget you can now create as many hard drive images as you want that can fit on your SD card and flip between them on the fly through the configuration menu.

the front panel gets old fast.

just remember to hit control C for a Warm reset when you swap disks in cp/m

[John Galt]

i forgot....

there is also a High density CP/M however you can only use the 1.2MB disks you can't mix sizes so you end up around ~5MB total storage

verse ~10.3MB with 2 hard drives and the 360k disks... but, again you can use on the fly compression to allow more to fit.

under Mp/M you can have 512MB cp/m disk sizes many people use the Z80pack and have Mp/M sessions under unix systems and connect remotely to them.

some people still program under Mp/M exclusively. (multi user cp/m)