Editing Macintosh IIx (section)

== Technical Details ==
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=== System Architecture ===
{| class="wikitable styled-table" style="width:90%; text-align:center;"
! Sub-system !! Specification (Macintosh IIx, September 1988)
|-
| '''CPU''' || Motorola 68030 @ 16 MHz • Integrated PMMU • 256 bytes I-cache + 256 bytes D-cache
|-
| '''Bus width''' || 32-bit data • 32-bit address (4 GB theoretical, 128 MB actual limit)
|-
| '''ROM''' || 256 KB ROM SIMM • "Dirty" ROMs require Mode32 for >8 MB RAM
|-
| '''RAM''' || 1-128 MB via 30-pin SIMMs • Two banks of four slots • 120ns or faster
|-
| '''Video''' || None built-in • Requires NuBus graphics card
|-
| '''Sound''' || Apple Sound Chip (ASC) • 4-voice stereo • 22.254 kHz sampling
|-
| '''Storage''' || 1.44 MB SuperDrive standard • Optional 40/80 MB SCSI hard drive
|-
| '''I/O Ports''' || ADB × 2 • Mini-DIN-8 serial × 2 • DB-25 SCSI • DB-19 floppy
|-
| '''Expansion''' || Six NuBus slots • 10 MHz bus speed • 10-40 MB/s bandwidth
|}

=== Memory Configuration ===

The IIx uses eight 30-pin SIMM slots arranged in two banks of four. Both banks must be populated with identical SIMMs within each bank.

{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''Memory Configurations'''
! Bank A !! Bank B !! Total RAM !! Notes
|-
| 4 × 256 KB || Empty || 1 MB || Minimum configuration
|-
| 4 × 256 KB || 4 × 256 KB || 2 MB || 
|-
| 4 × 1 MB || Empty || 4 MB || 
|-
| 4 × 1 MB || 4 × 1 MB || 8 MB || Maximum without Mode32
|-
| 4 × 4 MB PAL || Empty || 16 MB || Requires Mode32
|-
| 4 × 4 MB PAL || 4 × 1 MB || 20 MB || Requires Mode32
|-
| 4 × 4 MB PAL || 4 × 4 MB PAL || 32 MB || Requires Mode32
|-
| 4 × 16 MB PAL || 4 × 16 MB PAL || 128 MB || Maximum, requires Mode32
|}

'''Important notes:'''
* 4 MB and 16 MB SIMMs must be PAL (Presence Detect) type
* Mode32 or 32-bit System Enabler required for >8 MB configurations
* Bank A must be populated before Bank B can be used

=== ROM Specifications ===

The IIx requires a ROM SIMM in the dedicated ROM slot. The ROM is "32-bit dirty," containing 24-bit addressing code that limits RAM access to 8 MB without software patches.

{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''ROM Details'''
! Version !! Size !! Features !! Limitations
|-
| IIx ROM || 256 KB || SWIM support, 68030 optimizations || 32-bit dirty, 8 MB limit without Mode32
|-
| IIfx ROM || 512 KB || 32-bit clean alternative || Not officially supported but functional
|}

=== NuBus Architecture ===

The six NuBus slots provide the primary expansion capability:

{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''NuBus Specifications'''
! Parameter !! Specification
|-
| Bus speed || 10 MHz
|-
| Data width || 32-bit
|-
| Address space || 256 MB per slot
|-
| Bandwidth || 10-40 MB/s (theoretical)
|-
| Slot numbering || 9, A, B, C, D, E (hexadecimal)
|-
| Power per slot || +5V @ 2A, +12V @ 0.3A, -12V @ 0.3A
|}

'''Common NuBus cards:'''
* '''Graphics cards''' – Apple 8•24, Radius DirectColor/GX
* '''Accelerators''' – DayStar Digital PowerCache, Radius Rocket
* '''Network cards''' – Ethernet, Token Ring adapters
* '''Video capture''' – Media Time, VideoSpigot
* '''Additional I/O''' – Serial/parallel expansion cards

=== SuperDrive (FDHD) System ===

The IIx was the first Macintosh II series computer with built-in SuperDrive support:

==== Technical Specifications ====
* '''Controller:''' SWIM (Super Wozniak Integrated Machine) chip
* '''Capacity:''' 1.44 MB (high density), 800 KB (double density), 400 KB (single density)
* '''Encoding:''' MFM for 1.44 MB, GCR for 400/800 KB
* '''Compatibility:''' Mac, ProDOS, MS-DOS formats (with software)
* '''Transfer rate:''' Up to 62.5 KB/s

==== Drive Support Matrix ====
{| class="wikitable styled-table" style="width:80%; text-align:center;"
! Drive Type !! Internal Support !! External Support
|-
| 400 KB || Read only || Read only
|-
| 800 KB || Full support || Full support
|-
| 1.44 MB || Full support || Full support
|-
| MS-DOS 720 KB || With Apple File Exchange || With Apple File Exchange
|-
| MS-DOS 1.44 MB || With Apple File Exchange || With Apple File Exchange
|}

=== SCSI Subsystem ===

The IIx uses the NCR 5380 SCSI controller providing:
* '''SCSI-1 interface''' (5 MB/s maximum)
* '''Seven device support''' (ID 0-6, Mac is ID 7)
* '''DB-25 external connector'''
* '''50-pin internal connector'''
* '''Asynchronous transfers only'''

Real-world SCSI performance typically achieves 1.4 MB/s with appropriate drives and proper termination.

=== Audio System ===

The Apple Sound Chip (ASC) provides enhanced audio capabilities:
* '''Four-voice wavetable synthesis'''
* '''Stereo output''' via dual 8-bit DACs
* '''22.254 kHz standard sampling rate'''
* '''11.127 kHz and 7.418 kHz alternate rates'''
* '''512-byte FIFO buffer per channel'''

=== Power Specifications ===
* '''Input:''' 100-132V or 198-264V AC, 47-63 Hz (switch selectable)
* '''Maximum power:''' 230W
* '''BTU/hr:''' 786.6
* '''Power distribution:'''
** +5V @ 14.0A
** +12V @ 1.8A 
** -12V @ 0.25A
** -5V @ 0.1A
=== Power-On Circuit ===

The IIx features a complex power-on circuit that requires functioning batteries:

{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''Power-On Circuit Components'''
! Component !! Function !! Common Failure Mode
|-
| Dual 3.6V batteries || Provide 7V for power-on circuit || Dead batteries prevent power-on
|-
| UB1, UB2 transistors || Switch power supply control || Capacitor leakage damages transistors
|-
| C5, C6 capacitors || Filter power-on circuit || Leakage breaks nearby traces
|-
| R3, R18 resistors || Current limiting || Corrosion from capacitor leakage
|}

Without functioning batteries or with damaged power-on components, the IIx cannot start via the rear power button or ADB power key.