The Macintosh II-series has eight 30-pin SIMM slots organized in two banks, Bank A and Bank B (as shown above), addressed along a 32-bit data bus. Since the Mac II and Mac IIx utilize 8-bit memory devices, SIMMs must be installed in groups of four, and banks must be fully populated.There are three major variants of the Mac II-series:
- Macintosh II (Motorola 68020, 800k floppy drives)
- Macintosh IIx (Motorola 68030, 1.44MB SuperDrive floppy drives, updated ROM/SWIM)
- Macintosh IIfx (The original "wicked-fast" Mac, once coveted by power users worldwide. This page discusses the Mac II and Mac IIx variants only. The Mac IIfx will be addressed on a separate page, due to its significant deviations from previous logic board designs).
In the unmodified Mac II, the following memory configurations are possible utilizing standard 8-bit 30-pin 120ns SIMMs in 256K or 1MB densities. Note that denser SIMMs are typically placed in Bank A, and that best results are achieved by installing perfectly matched sets of SIMMs in each bank.
- 1MB - (four (4) 256k SIMMs in Bank A)
- 2MB - (eight (8) 256k SIMMs in Banks A and B)
- 4MB - (four (4) 1MB SIMMs in Bank A)
- 5MB - (four (4) 1MB SIMMs in Bank A, four (4) 256k SIMMs in Bank B)
- 8MB - (eight (8) 1MB SIMMs in Banks A and B)
In the Mac IIx and the Mac II, configurations exceeding 8MB are possible under the following circumstances:
- 32-bit system software is utilized (AUX or a variant of System 7 is required--these Macs originally shipped with System 6!)
- Apple 32-bit Enabler or Connectix Mode-32 must be installed under System 7.xx
- A PMMU, part number 630-8221, is required (original Mac II's shipped with an HMMU, part number 343-0002)
- 8-bit PAL-type 30-pin parity SIMMs rated at 120ns or faster, must be utilized.
As noted in Macintosh Memory Configurations, an undocumented ROM bug initially prevented the original Mac II from accepting SIMMs larger than 1MB in Bank A. Since Bank A and Bank B must be fully populated, the max configuration for a non-upgraded Mac II is limited to 68MB, with four (4) 1MB SIMMs in Bank A, and four (4) 16MB SIMMs in Bank B. Since denser pieces are typically installed in Bank A, as noted above, this configuration is an exception to that rule.
Fortunately, the SuperDrive upgrade kit (part number 34450062) included four updated Mac IIx ROMs (part numbers 342-0639, 342-0640, 342-0641, 342-0642), as well as a SWIM (Special Woz Integrated Machine) chip to replace the original IWM (Integrated Woz Machine) ASIC. The updated Mac IIx ROM enabled the use of both 4MB and 16MB SIMMs in Bank A. The theoretical maximum memory installable in an upgraded Mac II with Mac IIx ROMs, or in the Mac IIx itself, is therefore 128MB, in the form of eight (8) 16MB SIMMs.
The original Mac II motherboard was based on the Motorola 68020 processor running at 15.6772MHz with an optional built-in paged memory management unit (PMMU); it also included a Motorola 68881 math coprocessor. The Mac IIx saw the introduction of the Motorola 68030 and the 68882 coprocessor.
Specifications:
Logic Board RAM None. Supported SIMMs 256k, 1MB, 4MB, 16MB. Number SIMM Slots Eight (8). Supported VRAM None. Number VRAM Slots None. L2 Cache Supported None (Non-PowerPC architecture). SIMM Type 30-pin, PAL 8-bit, 120ns or faster.
As noted, the Mac II-series has no VRAM slots on the logic board. Video support is provided via NuBus cards in one of the four available slots.
The Guruz wish to express their sincere appreciation to Colleen Culbertson for providing us with the incentive we needed to get this page completed and posted.