Editing IBM PS/2 Model 25 (section)

== Storage and Expansion ==

=== Expansion bus ===

* '''Model 25 (8086)''': two '''8-bit ISA''' expansion slots on a riser. The upper slot is partially obstructed by the CRT cage, preventing full-length cards from fitting; only the lower slot is fully usable for long cards.
* '''Model 25 286''': two '''16-bit ISA''' slots on a riser, with an auxiliary 4-pin power connector for the 16-bit bus.
* '''Model 25 SX''': three '''16-bit ISA''' slots on a riser, with a fourth (flipside) slot used by the optional network card on the K01/L02 submodels.

=== Floppy interface ===

The Model 25 uses the '''PS/2 single-cable floppy interface''': power and data are carried in a single ribbon cable connecting the drive directly to the planar (no separate Molex 4-pin power lead). The interface is electrically different from PC/XT/AT 34-pin floppy interfaces. Drives are manufactured by ALPS, Mitsubishi, Sony, or YE-Data; Sony drives are the most likely to support 1.44 MB media on the original 8086 Model 25 even though it shipped only with 720 KB drives.

=== Hard drive interface ===

* The 8086 Model 25 has no hard drive support from IBM at launch. After-market kits used '''Seagate ST-506''' MFM drives in a 20 MB capacity, mounted in place of one of the floppy drives. The single-cable PS/2 interface includes the ST-506 lines.
* The Model 25 286 supports a '''30 MB ST-506''' drive on the same single-cable interface (submodels 8525-036 / 8525-G36).
* The Model 25 SX uses standard '''40-pin IDE''' at J10, with hard drive power supplied through the planar.

=== Power supply ===

* '''Model 25 (8086) monochrome (001, C02)''' &mdash; 90 W IBM PS/2 power supply.
* '''Model 25 (8086) colour (004, C05)''' &mdash; 115 W IBM PS/2 power supply (higher current required by the colour CRT).
* Both are 110/220 VAC switchable.
* The PSU has '''no Molex 4-pin drive connectors'''; drive power is delivered through the planar via the same single-cable PS/2 interface as the data lines.
* '''The Model 30 PSU is not a drop-in replacement''' for the Model 25 PSU &mdash; the planar connectors and pinouts differ.