A 8 bit fixed disk MFM controller from Germany
This rather unknown 8 bit hard disk MFM controller is made by CTT Munich from Germany. I don't know if it was actually manufactured there. I know however pictures of another HDD/FDD 16 bit controller of CTT on which "Made in West Germany" is written. Well then. The company CTT (Computertechnik und -technologie GmbH) seems to still exist today.
The hard disk controller is a NEC 7261AD ceramic chip with 12 MHz. So far I couldn't find any further documents about this controller on the internet.
- ROM BIOS: 0xC8000
- I/O Port: 0x320
- IRQ: 5
A defective tantalum capacitor can still be seen at C14. I soldered a new ELKO here; it works fine again. The other three capacitors will probably be replaced as well.
This Controller has it's own "FIXED DISK PRE-FORMAT UTILITY". Please use this! Please note the slightly different start address; C800:6 instead of C800:5. See also here.
Start low level formatting with:
DEBUG (ENTER) -G=C800:6 (ENTER)
The controller supports 12 fixed disks. I almost exclusively use the Seagate ST225. The ST225 is actually supported by every controller.
In total I have about eight ST225. These hard disks are simply indestructible. The only disadvantage is, they are a little noisy. But on the other hand, that's what makes "Retro Computing" so special.
- 306 cyl / 4 hds (ST213, ST412)
- 612 cyl / 4 hds (ST225)
- 733 cyl / 5 hds (ST4038
- 820 cyl / 6 hds (ST251)
- 940 cyl / 6 hds
- 940 cyl / 8 hds
- 462 cyl / 8 hds
- 820 cyl / 3 hds
- 855 cyl / 5 hds
- 855 cyl / 7 hds
- 306 cyl / 8 hds
- 733 cyl / 7 hds
If the controller does not recognize the hard disk parameters at startup, the low level formatting starts automatically! Currently I use this controller in my IBM XT 5160 test computer.
I have formatted a ST225 and a ST251 for test purposes and have not noticed any problems. The controller works fast and reliable. The nice thing about this card is that you don't have to plug in any jumpers.
A subsequent test with SpinRite II showed that this MFM controller works with an Hard Disk Data Storageinterleave of 1. This is really astonishing!