Author Topic: CP/M question...  (Read 3664 times)

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Offline Gryzor

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CP/M question...
« on: 12:44, 25 September 11 »
Ok, I've started readin the 664 manual for fun (heh...sunday morning :D ), and here's a snippet I don't understand:
Quote from: Amstrad PLC
[...]Since CP/M allows the use of multiple files by an overlay technique that permits programs that are larger than the RAM memory, the actual library disc may contain so many program files that there is little workspace left for the data


???

Offline TFM

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Re: CP/M question...
« Reply #1 on: 23:52, 25 September 11 »
That's about CP/M Plus. And it tells that you can put parts of program into the expansion RAM used by CPM. Or as an laternative, it talks about overlay files wich can be loaded by the main-program into the same RAM area, depending on which functions you actually need.
 
Examples for both would be Prowort or Stopp-Press (even if the latter one is no CPM program, but it's a good paradigm for overlay technique).
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Offline redbox

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Re: CP/M question...
« Reply #2 on: 23:57, 25 September 11 »
That's about CP/M Plus.

Are you sure?  CP/M Plus in the 664 manual...?

I thought it was only shipped with the 6128.

Offline MaV

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Re: CP/M question...
« Reply #3 on: 00:31, 26 September 11 »
It doesn't matter which CP/M version you use for the overlay technique, it works with 2.2 and plus. Usually the overlay files have the *.OVR extension. IIRC, Turbo Pascal uses it.
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Offline TFM

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Re: CP/M question...
« Reply #4 on: 00:42, 26 September 11 »
But Plus uses them even for the second bank! Therefore " that permits programs that are larger than the RAM memory" in a second dimension ;-)
 
Do you guys know the Z3Plus system?
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Offline steve

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Re: CP/M question...
« Reply #5 on: 00:48, 26 September 11 »
Ok, I've started readin the 664 manual for fun (heh...sunday morning :D ), and here's a snippet I don't understand:

 ???

As I see it, this means that you could almost or completely fill a 180k/360k disk with program files leaving little to no space for data files, you must put the data files on a second disk or turn the disk over.

Offline MaV

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Re: CP/M question...
« Reply #6 on: 00:49, 26 September 11 »
Z3plus? That's the rewritten CP/M optimized for the Z80. I haven't tried it yet. When it's time, and I start my Z80 CP/M computer project, then this will be the system of choice, I guess.
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Offline MaV

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Re: CP/M question...
« Reply #7 on: 00:51, 26 September 11 »
As I see it, this means that you could almost or completely fill a 180k/360k disk with program files leaving little to no space for data files, you must put the data files on a second disk or turn the disk over.

Yes, that's what the original text passage tries to tell us.
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Offline steve

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Re: CP/M question...
« Reply #8 on: 00:55, 26 September 11 »
I've heard of zcpr3.3, is that the same as z3plus?

EDIT: No, I think it is something different, is it better?

I am also thinking of putting together a CP/M system using the s100/696 bus, but I would like to split the operating system so it runs on 4 processors, one would look after the disk operating system, the second would run a multitasking OS based on a blend of MP/M, CP/M 3 and ZCPR 3.3, the third processor would run the "transient programs" and the fourth would handle the GUI/screen writing/editing, I could also use a processor just to handle interrupts and additional transient program processors using different architectures (6502, 9900, 68000 and 8086).
« Last Edit: 03:42, 26 September 11 by steve »

Offline TFM

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Re: CP/M question...
« Reply #9 on: 02:17, 26 September 11 »
Z3Plus is the CP/M Plus replacement.
 
ZCPR is the CP/M 2.2 replacement.
 
Both are more unix like. To complex to be explained in a post here, but worth to be examined.
 
i uses Z3Plus with a 20 MB hard-disc on the CPC and if I wouldn't have created my own OS, then it would be my OS of choice.
 
Check out gaby.de for example.
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Offline Gryzor

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Re: CP/M question...
« Reply #10 on: 17:58, 26 September 11 »
@steve: I think that if this was the case they wouldn't need to point it out... "overlay" must mean something else.

...so, how does overlay in memory work?

Offline MaV

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Re: CP/M question...
« Reply #11 on: 18:30, 26 September 11 »
@steve: I think that if this was the case they wouldn't need to point it out... "overlay" must mean something else.

...so, how does overlay in memory work?

I guess the most descriptive example of CPC software that works like that is Discology. You have one part of the program which acts as a control program )in Discology the menu) that loads whichever function you want to use (disc copying, disc editing, ...). Once you're done with one part you return to the main program and choose another option.

Now imagine that without a conscious effort to select options in a menu.

So, CP/M is more transparent, such that in Wordstar if you choose a particular function and it's not currently in memory, it will be loaded from disc - or in CP/M+'s case it can be loaded even from memory - and then executed. If it happens to be already in memory, it will just execute.
That way you can work with programs that contain a lot more functions than a 64k address space can hold, and you will also have more space free for user data (text files in Wordstar, DB-data in dBaseII, etc.) The downside is more disc accesses, and the program needs to be specially designed for overlaying to be possible.
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Offline almasys

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Re: CP/M question...
« Reply #12 on: 20:05, 26 September 11 »
Z3Plus is the CP/M Plus replacement.
 
ZCPR is the CP/M 2.2 replacement.
Ähem, they just replace the CCP.

Prost,
AMSi

Offline TFM

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Re: CP/M question...
« Reply #13 on: 21:28, 26 September 11 »
Ähem, they just replace the CCP.

Prost,
AMSi

Ok, the don't replace the BIOS in the AMSDOS ROM sure, but the add TCAP, HistoryShell, something like a text-GUI ;-), stuff like the wheel flag, and and and...
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Offline AMSDOS

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Re: CP/M question...
« Reply #14 on: 10:13, 01 November 11 »
Overlays were one of the featured provided when Turbo Pascal 3 came out (previous versions didn't allow this), which allows larger programs to be generated. I haven't used Overlays directly in my Turbo Pascal 3 programs as such, though the example on my website where I'm drawing a Mandelbrot onscreen, it's using 4x16Kb files to draw that Mandelbrot onscreen because it's plotting ink points rather than ink masks to produce the Mandelbrot, hence 64k of Data is going into that program.
 
So it's a bit like one of your Multiload games where it needs to load additional data when it comes to a new level, an area of memory is designed for that code to go into it when the situation arises. My Turbo Pascal 3 manual shows a simular kind of structure where you've got Main Program Code around an Overlay area, which can have a number of Overlay Procedures, not all running at the same time though. The best example I can think of is used in the GUI system Geno for CP/M 2.2. The main program deals with a series of Menu's, Disk Drives Detected, Displaying what's on those Discs and a couple of other things in the Menu's. In the Menu's though you can run the Text Editor which is an Overlay, another is for Copying Files and another one deals with the Printers for example and I think there's a couple of other ones. In them cases it's quite handy cause you have other programs as you need them by selecting them. They don't necessarily need CP/M Plus as with the case of Geno it only works in CP/M 2.2, though given CP/M is a Disk Based Operating System, they can be nifty to have!  :laugh:
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Offline Gryzor

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Re: CP/M question...
« Reply #15 on: 18:06, 03 November 11 »
I see... thanks for the explanation!!