Emulating Amstrad PC1512

My first computer was Amstrad Schneider PC1512SD  so it's understandable that I'm attached to that computer. I own two of them but since lately I don't have enough time to play with them I started to search for emulators to be able to try from time to time old software and games I've used. Since I lost some time to figure out how to emulate Amstrad, I decided to document everything in this blog post. This should be useful to me when I decide I want to play with it again in the future, but it can also help anyone else following my footsteps.

First I needed to find PC XT emulator. Modern day emulators/virtualization solutions like Qemu, VirtualBox, VMWare, and even Bochs do not support anything older than Pentium. So, some other emulator has to be used. After some time spending searching for XT emulators I found the following candidates:

1. MAME
2. PCem
3. PCjs

Turns out MAME and PCem support Amstrad PC1512 while PCjs doesn't. So I decided to go with PCem and MAME. After some trying I didn't manage to get anything from PCem. Namely, after starting emulation the screen was completely garbled so I decided to try MAME. I spent some time trying to figure out how to emulate Amstrad using MAME. Here is the essence of it on Fedora 27:

1. First, you need to install mame package. This package is present in Fedora repository so except of 'dnf install mame' no additional configuration is necessary.
2. Next, you need to obtain ROM images from Amstrad. After some (actually a lot of) Googling I managed to find them. If I remember correctly, I obtained them via MAME ROMS package.

ROMs that you should have are any of the following three ones:

1. Version 1 ROMs: 40044.ic132 (8kB, SHA1: 7781d4717917262805d514b331ba113b1e05a247) and 40043.ic129 (8kB, SHA1: 74002f5cc542df442eec9e2e7a18db3598d8c482)
2. Version 2 ROMs: 40044v2.ic132 (8kB, SHA1: b12fd73cfc35a240ed6da4dcc4b6c9910be611e0) and 40043v2.ic129 (8kB, SHA1: c376fd1ad23025081ae16c7949e88eea7f56e1bb)
3. Version 3 ROMs: 40044-2.ic132 (8kb, SHA1: b77fa44767a71a0b321a88bb0a394f1125b7c220) and 40043-2.ic129 (8kB, SHA1: 18a17b710f9eb079d9d7216d07807030f904ceda).

The names are as expected by MAME. In addition there'll be some other ROMs too:

1. 40045.ic127 (8kb, SHA1: 7d858bbb2e8d6143aa67ab712edf5f753c2788a7)
2. 40078.ic127 (8kB, SHA1: bc8dc4dcedeea5bc1c04986b1f105ad93cb2ebcd)
3. wdbios.rom (8kB, SHA1: 601d7ceab282394ebab50763c267e915a6a2166a)

The first two are, I believe, fonts while the third one is necessary only if you want to emulate HD version of PC1512.

Create in the current (working) directory folder named pc1512 and place selected ROMs into it.

We can now start emulator. Use the following command line:

$ mame pc1512 -rompath . -window -uimodekey DEL_PAD

The first argument to MAME emulator is machine that should be emulated, in our case its PC1512. The option rompath instructs MAME to search for ROMs in the current directory. In our case it'll search for folder named pc1512 and within it for ROMs names as given above. The the option window prevents MAME from going fullscreen (and I had some problems exiting). Finally, the option uimodekey defines escape key to access internal menu.

This will give famous "Pleas wait..." message from BIOS and then "Insert SYSTEM disk into drive A" message. Now we are at the point of providing boot disks to the emulated machine. For that it is necessary to obtain images of Amstrad PC1512 disks. You can find them here. The problem is that disks 1 and 4 are given in CFI format (Compressed Floppy Image, created by tool FDCOPY.COM), while disks 2 and 3 are archives.

So, after unpacking disk 1 (46001.Zip) and disk 4 (46004.Zip) you are presented with files 46001.CFI and 46004.CFI which are not recognized by MAME. To convert them into appropriate format use the following command:

dsktrans -itype cfi 46001.cfi 46001.dsk

dsktrans is a tool that is part of libdsk-tools package, also part of the Fedora repository. So, just run 'dnf install libdsk-tools' and that should be it. After converting 1st disk you can also convert 4th disk.

Now, we are ready to start MAME with system disk provided. One way to do that is to open internal MAME menu after staring PC1512 and then attaching disk image. The other way is to use command line:

mame pc1512 -rompath . -window -uimodekey DEL_PAD -flop 46001.dsk

The new option is flop that defines image to be used as a floppy in a floppy disk. By the way, to find out supported floppies you can use the following command:

mame pc1512 -listmedia

and take a note of (brief) column.

What happens now is that you are provided with MS DOS command prompt in emulated machine.

The next step is to start GEM, but before that I have to find out how to create floppy disk image. Note that the tools imgtool that is part of MAME gives segmentation fault on almost any command you try. Anyway, stay tuned for GEM...

Some useful resources I found while working on this:

• Amstrad XT Pages
• Cliff Lawson Amstrad pages

Retro computing resources

From time to time I like to search on the Internet stuff related to retro and vintage computing. This time my interest was (again) resolving around a wish to try Xenix. Namely, Xenix was a Unix variant written by Microsoft that could be run on IBM PC XT with 8086 microprocessor. While searching where to download Xenix, I stumbled on a WinWorld site which has many other vintage operating systems available for download. So, a lot of stuff to try. Later, I discovered that there is also software shipped as part of a MAME ROM package. You can browse it here.

Obviously, to try them it is necessary to have an emulator. Note that virtualization solutions like QEmu, VirtualBox, VMWare and similar don't fit here because they emulate modern hardware, or they only virtualize existing hardware. So, I tried to find emulator that emulates PC XT/AT, but also emulators that would allow me to run software for other platforms. After half day search, I decided to write this post with everything I found so far.

One site with some kind of a database of a different emulators is Zophar's Domain. It isn't particularly up to date, but nevertheless it lists a lot of emulators with different categorizations so I think it's very useful. Later, I found several other similar sites:

• Emulation General Wiki
• Wikipedia list of computer system emulators 
• DMOZ directory with emulators

Zophar's site helped me to find emulator for IBM PC XT/AT, namely PCE. This particular emulator emulates a lot more hardware than just IBM's, and what's more interesting is that the author already prepared different configurations for you to download and try. Specifically, there is Xenix 2.13 to download and try. Just one note, these archives are for Windows machines, so if you are - like me - on Linux, download first PCE's source, compile it and then use it instead of provided EXE files. Anyway, I tried it and it worked flawlessly.

As it turns out, there are some other IBM PC XT/AT emulators:

• The first one is 8086tiny. It claims to be the smallest emulator there is. But, I haven't had a lot of success in trying it.
• In case you want something that runs within a Web browser, then you'll be interested in PCjs, i.e. JavaScript emulator. Source is available here. This one seems to be actively developed at the time this post was written.
• The MAME emulator.

And this last one is interesting enough for me to devote few paragraphs to it. MAME is emulator that emulates multiple different machines. What was interesting to me is to try several ones:

• Orao
• Amstrad PC1512

In each case I had to find appropriate ROM files. In the end, the most useful site was Emuparadise. After downloading zip files, I unpacked them into a directory named after the machine as identified in MAME itself and then started the emulation like this:

mame -rp . orao

or in case of Amstrad

mame -rp . pc1512

In each case the option -rp specifies that the current directory should be searched for rome files, while the other argument is driver/machine to be emulated. Note that ROM files will be searched for in the directory named as driver/machine. It happened in some cases that not all ROM files were present, but I managed to find them in other archives on the same site.

For the end, here are some additional interesting links I stumbled on:

• Blog with some posts related to XT
• Documentation about IBM 51xx PC Family Computers including ROM files. There is a lot more information there.
• The Old School Emulation Center (TOSEC) and mirror

Using ~ as a shortcut for home directory...

I just stumbled on the question why tilde (~) is used as a shortcut for home directory on Unix. It's very interesting since it never occurred to me to ask this question? :)

Then, there are lot more questions like that one on StackExchange, here is a selection of some interesting ones (to me at least):

• Why is . and .. used for current and parent directories. The answer isn't so clear as for tilde, but it turned out that hidden files (those whose name begins with a dot) are actually consequence of a bug in early versions of ls command (source and Wikipedia page).
• What does /etc mean?
• What was the shell used before Bourne shell?
• Why is dash (-) used to denote options?
• Why isn't umount spelled unmount?
• What is the origin of 'root' account? But note that this question isn't definitely resolved.
• What is the origin of wheel group name?

And, for the end, here is why vi uses hjkl for cursor movement.

Computer units sold...

I stumbled on the following article that has a graphic about different computer units sold per year from 1975 until 2011. I reproduced it here for a completeness:

It's obvious that by "computer units" is meant both personal computers and mobile phones. Anyway, this graphic is very interesting even though many popular units are missing, e.g. Spectrum, Amstrad, Commodore 128, some Atari models. This graph was taken from Asymco.

What this make me wonder is if there is some page with this data in one place, so that curious person can play a bit with that data. Quick googling didn't reveal much. I tried expressions like c64 units sold, or home computer units sold per year.  Still, I found some quite interesting pages. I'll list them here, and if it happens that you know where I can find all the data I was looking for, please do tell me! The most interesting, and relevant, page I found is an article on Wikipedia about Console wars in which some data can be found. This page also has a plenty of references, which I didn't pursue further. Also, while googling, this page frequently appeared. The interesting thing in that particular article is how they estimate number of C64 units sold per year using serial numbers! The method used is actually much older, it dates back to WWII when Allies used it to estimate number of tanks German army produced. Serial numbers of C64 computers were obtained from the Web site that collects C64 serial numbers. Using this method and data the article estimates that there were 12.5 million units of C64 produced.

All in all, very interesting stuff, but it seems that it would require much more time than I devoted to it, and that I'm ready to devote to it. :)