Slim Cards
"Slim Cards" are a piece of hardware that it appears Apple was designing for the Macintosh Portable but I'm unsure whether they ever existed.
This likely would have been two slots above the floppy drive, likely taking the place of the hard drive.
These card slots would be connected to an adapter in the PDS slot.
The cards would have been some form of non-volatile storage, such as flash memory or ROM, and would be directly mapped into the upper 4MB of RAM space from 0x500000 to 0x8FFFFF.
They could be up to 2MB in size and were sized in 512KB segments. Slim card 0 would map to 0x500000 up to 0x6FFFFF, and slim card 2 would map from 0x700000 up to 0x8FFFFF.
The maximum amount of RAM that can be installed with a slim card adapter installed is 5MB. The memory sizing routine checks the register at 0xFC0200 for bit 3, and only sizes up to 5MB if detected.
The cards could be inserted and ejected while the OS is running, unlike ROM disks.
Slim Card Registers
| Location | Description |
|---|---|
| 0xF00000 | Bit 3: Slim 0 inserted Bit 2: Slim 0 is ROM or write protected |
| 0xF00010 | Bit 3: Slim 0 eject register (0 to eject) |
| 0xF00020 | Bit 3: Slim 0 write protect |
| 0xF00030 | Bit 3: Slim 1 inserted Bit 2: Slim 1 is ROM or write protected |
| 0xF00040 | Bit 3: Slim 1 eject register (0 to eject) |
| 0xF00050 | Bit 3: Slim 1 write protect |
| 0xFC0200 | Bit 3: Slim adapter installed |
Slim Adapter ROM
The slim card adapter has the ability to execute code from additional ROM. If bit 3 of 0xFC0200 is high indicating that a slim card adapter is installed, 0xE00000 is checked to see if it contains SLIM ROM. If it does, code is executed from 0xE00008.