Egregoros

huh, i reconnected everything and plugged the drive into my HP85, and it actually works! i can read the files on it.

one of the programs.

unfortunately the floppy drive isn't quite working. i can't format this new disk. the drive makes a very rattly sound, so it's probably something mechanical.

3 1/2" = light mode
5 1/4" = dark mode

got some time to take the drive out again and clean it again. i ended up having to remove this entire sliding side plate because there was still some old crusty lubricant. it is much better now. i also lubricated the head stepper worm gear.

much better, it actually formats the disk! BTW this 3 1/2" format is very odd. 600 rpm, 66 tracks, 16 sectors per track, single-sided, 270K capacity, 256 byte sectors.

why all this work? i need to work with some very early 3 1/2" disks. this example has an oval window but more surprisingly, the disk shutter must be opened manually before you put the disk in the drive!

and it actually reads! at least, it recognizes the LIF volume label. the filesystem is for a different type of computer, so the HP85 doesn't show any files.

some might be curious about the format of the disk. here's the view in HxC. zero bad sectors! they are standard IBM MFM sector format, 256 bytes per sector, but there's a 17th "narrow" 128 byte sector that stores a media wear counter.

i'm dumping the original hard drive again, but this time using the EBTKS.

so the difference with the MFM dump is that it includes spare empty sectors that are skipped by the 9133A drive controller. looks like each track only has 31 sectors with 1 spare, totaling 32. a little confused about the initial offset of 0x1e00 for the first spare sector. the next spare sectors are at 0x3d00 and 0x5c00.

you might be wondering what those weird 3 1/2" disks were for: it is this very odd beast, the HP 125. this is a dual processor CP/M machine that uses Z80s. one of them is the main CPU and the other runs the terminal I/O!

the form factor is super weird. it, along with the 2621 terminal, were known as the "Alien Heads."

it's a bit tricky to install CP/M on the hard drive, so i will go through the process here. first, the machine always boots from HPIB drive 0, so set it up with the floppy drive at 0 and the hard drive at *2*.

then place a CP/M boot diskette in the machine and power it up. then from the welcome screen, hit UTILITIES and then FORMAT. the hard drive will appear as drive E, F, G, and H. i had it format drive E.

exit to the welcome screen, and then select UTILITIES and then COPY. hit CHANGE COPY until the selection says SYSTEM (not ALL or DATA). select the source drive as A and the destination drive as E. this copies the CP/M operating system to the hard drive.

now turn off the computer and swap the drive DIP switches around so the floppy disk has ID 2 and the hard drive has ID 0. when you turn the computer back on, it should automatically boot CP/M!

however, the basic install of CP/M doesn't include any utilities other than the build in commands, so you'll need to go E:PIP A:=E:PIP.COM to copy the PIP program to the hard drive, which you'll use to copy more programs. then you can repeat this for any other utilities you want on the hard drive, like FORMAT, STAT, COPY, SUBMIT, XSUB, or the other software that HP released.

HP's version of CP/M will try to run WELCOME.COM which displays the GUI. i find it annoying, so i just renamed it to WELCOM2.COM using REN.

here's what i have installed so far. besides microsoft basic, there is also the CP/M assembler (ASM), editor (ED), and loader (LOAD), as well as the dump utility and the dynamic debugger (DDT).

NARRATOR: it was NOT a convenient way to edit text files.