Oh, you're right about the 4164. I'm just blind.
It still seems like a somewhat strange design. I've been repairing a broken Commodore PET 2001-N for the last few months (yes, it has a *lot* wrong with it), and I recalled it used a pair of 74LS244s in front of the DRAM bank wired so they're bi-directional. (The data pins on both sides are tied to a pair of opposite-facing bus drivers and the enable lines for the two sets are tied to "READ" and "WRITE" signals respectively. See:
http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/2001N/320349-5.gif
The PET has a number of sets of 244's wired like this. There's a "main set" in front of the 6502 which are always-on drivers, and then there are sets tied to read/write and chip select circuitry in front of main RAM and the video subsystem.)
I guess what I also half-remembered was... looking at the schematics again, the DI and DO lines of its DRAMs (4116's, but very similar to 4164s) are *also* tied together and share a single bi-directional line from the DRAM sockets. Thus I remembered a "single line" but failed to remember that it originated from two pins, leading me to faultily assume that DRAMs "breathed in and out" the same line like SRAM. My bad.
Now the fact that there's two sets of "busses" above and below the DRAM chips on the Mac schematic makes a lot more sense to me. Durrr! Sorry about that. :^/ I'll put my pointy hat back on.
It still seems like a somewhat strange design. I've been repairing a broken Commodore PET 2001-N for the last few months (yes, it has a *lot* wrong with it), and I recalled it used a pair of 74LS244s in front of the DRAM bank wired so they're bi-directional. (The data pins on both sides are tied to a pair of opposite-facing bus drivers and the enable lines for the two sets are tied to "READ" and "WRITE" signals respectively. See:
http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/2001N/320349-5.gif
The PET has a number of sets of 244's wired like this. There's a "main set" in front of the 6502 which are always-on drivers, and then there are sets tied to read/write and chip select circuitry in front of main RAM and the video subsystem.)
I guess what I also half-remembered was... looking at the schematics again, the DI and DO lines of its DRAMs (4116's, but very similar to 4164s) are *also* tied together and share a single bi-directional line from the DRAM sockets. Thus I remembered a "single line" but failed to remember that it originated from two pins, leading me to faultily assume that DRAMs "breathed in and out" the same line like SRAM. My bad.
Now the fact that there's two sets of "busses" above and below the DRAM chips on the Mac schematic makes a lot more sense to me. Durrr! Sorry about that. :^/ I'll put my pointy hat back on.