Editing IBM PS/2 Model 70 (section)

== Planar ==

The Model 70 planar carries:

* '''CPU''': 80386DX, PGA-132, socketed. The socket is shared between the discrete 80386 (in E61 / 121 / A21 / A61) and the '''Power Platform''' daughtercard (in B21 / B61).
* '''Optional 80387DX coprocessor''' in a socket adjacent to the 80386DX.
* '''Memory''': 4 × 72-pin SIMM sockets accepting 1, 2 or 4 MB modules. Maximum 16 MB (4 × 4 MB) on planar. PS/2 72-pin SIMMs are '''proprietary''' to IBM PS/2 — they have a different pinout and parity convention from later PC 72-pin SIMMs.
* '''RTC''': Dallas DS1287 / DS12887 (24-pin DIP marked "DALLAS") with integrated lithium cell.
* '''Onboard VGA''': IBM VGA implementation with 256 KB of dedicated VRAM. VGA controller chip and VRAM are on the planar.
* '''MCA bus controller''': 32-bit MCA implementation, providing three 32-bit MCA slots.
* '''Floppy controller''' integrated on the planar with single-cable interface.
* '''Surface-mount aluminium electrolytic capacitors''' for IC bypassing throughout the planar. '''These are the famous PS/2 SMD caps that leak after 30+ years and cause the Model 70 to die slowly.'''