Editing Macintosh Plus (section)

== Technical Details ==
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=== System Architecture at a Glance ===
{| class="wikitable styled-table" style="width:80%; text-align:center;"
! Sub-system !! Specification (Macintosh Plus, Jan 1986)
|-
| '''CPU''' || Motorola 68000 @ 7.8336 MHz  (15.667 MHz ÷ 2)<ref>{{cite web |url=http://www.easy68k.com/paulrsm/doc/dpbm68k1.htm |title=Design Philosophy Behind Motorola's MC68000 |author=Thomas W. Starnes |publisher=BYTE Magazine |date=April 1983 |access-date=2025-01-25}}</ref>
|-
| '''Bus width''' || 16-bit data • 24-bit address  (16 MB logical)  
|-
| '''ROM''' || '''128 KB "v4.0"''' Toolbox / HFS / SCSI Manager
|-
| '''RAM''' || 1 MB on four 256-K × 1 DRAM SIMMs — expands to '''4 MB''' via 30-pin SIMM slots  
|-
| '''Video''' || 512 × 342 monochrome frame-buffer (22.1 KB) DMA-shared with system RAM  
|-
| '''Sound''' || 8-bit PWM DAC via VIA timers • 22 kHz RC low-pass → LM380 amplifier  
|-
| '''Disks''' || Sony OA-D34V-22 800 KB auto-inject 3.5″ floppy  
|-
| '''I/O ports''' || DE-9 mouse/KB • DB-19 ext. floppy • '''DB-25 SCSI-1''' • RS-422 serial × 2 • 3.5 mm audio-out  
|}

=== Memory Map (Physical) ===
{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+'''Macintosh Plus Address Space'''
! Range !! Size !! Purpose
|-
| $000000 – $3FFFFF || 4 MB || '''DRAM''' (configured 1 MB – 4 MB)
|-
| $400000 – $41FFFF || 128 KB || '''ROM''' (v4.0 Toolbox)  
|-
| $480000 – $4BFFFF || 256 KB || '''I/O A''' – VIA 1, VIA 2, SCC, IWM, VBL PAL  
|-
| $580000 – $5BFFFF || 256 KB || '''I/O B''' – WD 5380 SCSI DMA registers  
|-
| $600000 – $FFFFFF || Mirrors / reserved
|}

''Frame-buffer note: still occupies the last 22 016 bytes of physical RAM (e.g. '''$3FE000 – $3FFFFF''' in a 4 MB system).''