The diskless PCjr

[hyperfrog]

I'd like to have a diskless PCjr. I hate floppy disks. I want to eliminate them all. But this is a long-term objective. (I have a few other projects to carry on first.)

It appears that DR-DOS and ROM-DOS are embeddable, but the free versions of those DOSes are not. One would need to purchase a developer kit in order to build a ROM disk containing the DOS startup files and perhaps a few drivers.

However, I devised a method for achieving something similar using any version of DOS. It is something along the lines of "hibernation" in Windows. Here's an outline:

1. You boot the computer into your favorite DOS.
2. You set up a RAM disk, copy COMMAND.COM to it, and tell DOS that this is where COMMAND.COM is to be found from now on. You also copy other useful files to the RAM disk (e.g. your network adapter's packet driver).
3. You run a special program that will take a snapshot of all allocated RAM, and write it to disk. (Yes, such a program needs to be written.) Note that this snapshot will contain, among other things, the files you copied to the RAM disk. Some form of data compression could be handy or even necessary.
4. You take the snapshot disk, and use it to burn a special EPROM that gets invoked when the PC is cold-started. (This seems to be relatively easy to do.) The EPROM would contain the snapshot you created, plus some code that will restore the snapshot into RAM. Note that this could be a "big" EPROM containing the BIOS plus the additional code and the snapshot.
5. You turn off your PC, and install the new EPROM.
6. You turn on your PC. The BIOS does its job, and then transfers the control to the "Option ROM", wich restores the snapshot.
7. The PC is back on his feet, and the RAM disk contains the files you copied to it before the snapshot creation.

There are probably some pitfalls. For instance, if a piece of hardware gets initialized by a device driver loaded from CONFIG.SYS, it won't get initialized the second time you turn on the PC. The device driver will be restored into RAM, but the hardware device itself may not be in the proper state (it's been reset when you turned off the PC). However, any file that normally gets loaded from the command line or a .BAT file could be loaded after the snapshot restoration, provided you copy those files to the RAM disk prior to the snapshot creation.

Any PCjr guru interested in providing some guidance? Mike?

Christian

[hyperfrog]

Well, it appears that DR-DOS is only $35 after all. I will inquire whether it includes the ROM utilities. I will also try to have the PCjr boot one of the free versions. To be continued...

Christian

[Brutman]

Have you considered going diskless, but using a network device instead?

The PCjr cluster adapter was able to 'remote IPL' (remote boot) from a server on the network if the diskette drive was not installed or a diskette was not present. Other machines/operating systems could do this too, and it still happens today - DHCP is an offshoot of the BOOTP protocol which diskless Unix workstations used.

If I were going to experiment with this I would learn how to write BIOS extensions that could be used to grab boot code from a remote machine, similar to what the Cluster adapter does. Embedded DOS (your option) would be good for fast boot or a standalone machine.

[hyperfrog]

Yes, I thought about BOOTP. However, I think I'd rather have Jr boot on it's own. No network adapter required, no cable... You flip the power switch, and Jr is up and running a couple of seconds later. It would allow networking without imposing it on you. Besides, when COMMAND.COM needs to be reloaded, having it on a ROM disk would really speed things up.

Christian