Actually, it's been too long... Was it G c800:5, or g=c800:5? Either way, that was the debug code to fire up the ROM based disk formatting utility on the Seagate and Western Digital 8 and 16 bit MFM controllers. IIRC, the WD-1007 ESDI controllers used the same address, however, the WD-1006V RLL controllers used CC00:5.
And yes, the drive geometry for the Seagate 40 megabyte MFM drive (the Seagate ST-251. The difference between the 251-0 and 251-1 was 65ms vs 40ms access time - or was it 40 and 28ms? Either way, it no longer matters when a cheap video card has more than 3 times the RAM than these old hard drives, once considered by many to be more than you'd ever need on a server!). 820 cylinders, 6 heads, 17 sectors/track.
Another one I have memorized is the 40MB Mitsubishi MR535. 977x5x17, though it WAS certified to run as a 65MB RLL drive. And WOW! Did they run HOT!!!!!
Mark
You probably have something still running with an ST-225, hooked up to a WD RLL controller to get another 10MB out of it.