Al Kossow wrote: Well, thats not quite right. I have long understood that real disk file system functionality will require 32K words at a minimum. For the HP 1000's, the 21MX processors offer some microcode tricks in the DMS instructions that greatly simplify building a DOS, but using these eliminates large 2116's and 2100A/S's from running the code. The core O/S as it stands now already provides very usable and realistic support for smaller and slower CPU's. Whats missing now is the DOS functionality for 'larger' machines. We may end up limiting DOS functionality to 21MX machines with DMS, but will make an effort not to. This is exactly the genisis of what we call HP-IPL/OS. At one time, when I still had my NOVA's, there was going to be a parallel effort on DG-IPL/OS. Similar vairents could be generated for any vintage machine, like IMLAC-IPL/OS, etc. in exactly the same way that FORTH is bootstrapped onto a new CPU. In fact, much of the IPL language is written in IPL, not unlike a LISP machine O/S being written in LISP. Being a modular threaded interpreter, you can take a single binary kernel that runs on anything from a 4K 2114 up to a 21MX processor, and load just whats needed for your configuration. Because you first bootstrap the HP processor from a host, IPL/OS can run as a parasite machine hung from a serial port with no vintage peripherals (other than serial interfaces). As you bring peripherals on-line, or build emulations, you download new code blocks until you have a totally self-sufficient operating system with a DOS and source-code editor, etc. Its just a series of layers wrapped around the same common threaded engine at the core. I think the inner interpreter is only 23 words or so. An excellent approach for machines without native peripherals. In the case of the HP 1000's there is an I/O card that is ideal for this, its a 4 Mhz Z80 with 16 mb of DRAM, and 16K of EPROM. It has a fast DMA interface to the HP backplane, and several advanced Z80 SIO-type chips to talk to an external system. The problem is developing the Z80 code to talk to something outside the box. but should you come across the documentation for HP's programmable serial interface board, I've got the hardware.