Known Problems

Here are some well known problems and how to solve them (or... not).

Hard-drive doesn't spin up - "stiction" issue
Only 16 MB of RAM available on systems with SX/SLC CPU

Hard-drive doesn't spin up - "stiction" issue

From Peter:
Many older hard-drives tends to hang at Power On. It is a result of adhesive-power between disk surfaces and r/w-heads - so called "stiction". The surfaces are very plain polished and the heads really 'suck' on them. The spindle motor has not enough torque to loosen the platters from the heads. This effect appears sometimes after the computer was off for a longer time (but it can also happen after short period of time, especially if the drive already had the stiction problem before).

There's no 'soft' solution, but here are few options, how to get your drive running again (your mileage may vary):

Option 1:
Several Power On cycles (20 sec. On, then 20 sec. Off) may start the drive... or blow up the power-supply. And is no good treatment for the electronic components at all.

Option 2:
Unplug the system-unit from everything, shake it (up/down several times) then rotate the unit with a sharp kink clockwise some times. Plug it on again and Power on. The heads should have released and the drive spins up.

Don't lift the unit up on the frontside and let it crash back on the desk.
This method will definitely kill your harddisk very soon.

I have had good success with putting the system-unit on the rear seat of my car and drive to town, let the car on a sunny parking lot, go shopping, come back, drive home and plug it back on. Afterwards the drive runs again. Changes of temperature and the vibrations have caused the heads to release from the disk surfaces.
Disadvantage: my friend tried the same with his Model 55. Some guys broke his car open and stole the computer.

Option 3:
On some drives you can access the spindle motor if you remove the control board. Then you can very carefully spin the motor (and thus platter inside the HDA), hopefully removing the stiction problem and not snapping the R/W heads in a process.

Important! In either case you have badly treated your Harddisk and it is a good idea to begin backing up the data!

This issue seems to be common on Seagate ST-177I 60MB harddisk used in many Models 55SX (8555-061) and in some Models 70 (70-061).

(Ed. Tom: Edited and extended with some extra notes and tips.)

Only 16 MB of RAM available on systems with SX/SLC CPU

From Peter:
In a brief: you can't install more than 16 MB on machines with a 386SX/SLC, 486SLC, SLC2 or SLC3 processor.

"Oh - sure, but my 9556 has a 486!"
"Really? Wasn't it a 486SLC?"
"Uhm... er, yes... think so!"

Gotcha! The 486SLC, SLC2, SLC3 are also 386SX-based chips. Ever wondered why they offer just a 387SX as math co-processor? Now - that's the reason. The 486SLC family has internal L1 cache like a 486 and some of the newer instructions, but externally they are a 386SX. And these have only a 16-bit data bus and 24-bit address bus and thus can only address 16 MB of memory.
24 address lines = 2 ^ 24 bytes of addressable space = 16.777.216 bytes
These processors are from the technical point of view similar to the 286-line CPUs, but have 32-bit registers and other features of 386/486 CPUs, which allows them to run 32-bit software. They can even carry out 32-bit busmaster functions, unless they have only 16-bit MCA connectors (the short ones).
But the address-space is limited to 16 MB due to the lack of address lines.

Sad but true.

Tomas Slavotinek says:
   Some SX/SLC systems will recognize memory over the 16 MB limit and show the correct capacity of "Installed Memory" in "View Configuration" menu of the Ref. disk. This information is there (probably) only to let the user know that he has more memory installed, than his system can use. "Usable Memory" line on the same screen shows amount of memory actually available to operating system and applications.

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