Editing Macintosh Classic (section)

== Technical Details ==
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=== System Architecture at a Glance ===
{| class="wikitable styled-table" style="width:90%; text-align:center;"
! Sub-system !! Specification (Macintosh Classic, Oct 1990)
|-
| '''CPU''' || Motorola 68000 @ 7.8336 MHz (15.667 MHz ÷ 2)
|-
| '''FPU''' || — (none; not socketed)
|-
| '''Bus width''' || 16-bit data • 24-bit address (16 MB logical)
|-
| '''ROM''' || '''512 KB “SE/30-class”''' ROM SIMM (v7.0) — 32-bit clean, HFS+, Color QD
|-
| '''RAM''' || 1 MB soldered • '''Expansion card adds 1 MB + 2 × 30-pin SIMM slots → 4 MB max'''
|-
| '''Video''' || 512 × 342 monochrome — 22.1 KB DMA steal from main DRAM
|-
| '''Sound''' || 8-bit PWM DAC via VIA timers • 22 kHz → RC filter → LM380 amp
|-
| '''Disks''' || Internal Sony SWIM-II 800 KB (FDHD option 1.44 MB) • 40 MB SCSI HDD (BTO)
|-
| '''Ports''' || ADB • DB-19 ext. floppy • DB-25 SCSI-1 • Geo/SCC serial × 2 • 3.5 mm audio-out
|-
| '''Expansion''' || '''No PDS'''; memory–I/O expansion via proprietary 96-pin mezzanine card
|}

=== Memory Map (Physical) ===
{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+ '''Macintosh Classic Address Space'''
! Range !! Size !! Purpose
|-
| $0000 00 – $0FFF FF || 1 MB || '''On-board DRAM'''
|-
| $1000 00 – $4FFF FF || 4 MB || '''Expansion DRAM''' (if present → 4 MB ceiling)
|-
| $4000 00 – $47FF FF || 512 KB || '''ROM SIMM''' (v7.0)
|-
| $5000 00 – $50FF FF || 64 KB || '''I/O bank A''' – VIA 1/2, SCC, SWIM-II, ADB, VBL PAL
|-
| $5800 00 – $58FF FF || 64 KB || '''SCSI NCR 53C80 regs + glue'''
|-
| $5C00 00 – $5FFF FF || 256 KB || '''Expansion card decode''' (memory & option EEPROM)
|-
| $9000 00 – $9000 FF || 256 B || Frame-buffer shift register (mirrored)
|-
| $C000 00 – $FF FF FF || Mirrors / reserved
|}

=== ROM SIMM Layout (512 KB, v7.0) ===
{| class="wikitable styled-table" style="width:90%;"
! Offset !! Size !! Module
|-
| $4000 00 || 16 KB || 68000 vectors & Mini-Shell
|-
| $4004 00 || 64 KB || QuickDraw 1.3 (monochrome & color, 32-bit)
|-
| $4014 00 || 192 KB || Toolbox, Window/Menu mgrs., SANE FP
|-
| $4044 00 || 80 KB || SWIM-II floppy, ASC sound, ADB Egret
|-
| $405E 00 || 96 KB || SCSI Manager 4.3, Disk Cache, HFS/HFS+
|}

=== SWIM-II Floppy Controller ===
* 800 KB GCR variable-speed (standard)  
* FDHD build-to-order: 1.44 MB MFM + 800 KB GCR (autodetect)  
* Supports intelligent-step motor timing; faster reads on outer tracks.

=== SCSI & Mass-Storage ===
* '''NCR 53C80''' 8-bit controller — 5 MB s⁻¹ sync (≈1.1 MB s⁻¹ async real-world)  
* “Pseudo-DMA” using block-moves by CPU; internal drive on 50-pin ribbon.

=== Key I/O ICs ===
* '''6522 VIA × 2''' — system timers, sound PWM, keyboard‐handshake  
* '''8530 SCC''' — dual RS-422 serial (up to 230 kbps)  
* '''SWIM-II''' — floppy & GCR/MFM selector  
* '''NCR 53C80''' — SCSI  
* '''Egret (68HC05)''' — ADB, soft-power, PRAM battery  

=== Sound Path ===
68000 → VIA Port A (8-bit sample) • VIA Timer 1 @ 22.254 kHz toggles Port B → PWM → RC filter → LM380 → speaker / rear jack.

=== RAM Expansion Notes ===
{| class="wikitable styled-table" style="width:75%; text-align:center;"
! Total RAM !! Expansion Card SIMMs !! Jumper
|-
| 2 MB || none (card only) || “No SIMMs” (JP top)  
|-
| 2.5 MB || 2 × 256 KB || “With SIMMs” (JP bottom)  
|-
| 4 MB || 2 × 1 MB || “With SIMMs” (JP bottom)  
|}

* SIMMs: 30-pin, 120 ns, 8-chip, non-parity only.  
* Mixed sizes not supported; SIMMs must match pair.

=== Performance Benchmarks ===
{| class="wikitable styled-table" style="width:70%; text-align:center;"
! Test (MacBench 1.0) !! Score !! vs Mac Plus
|-
| CPU integer || 115 || × 1.43  
|-
| Disk (40 MB SCSI) || 230 || × 1.92  
|-
| Graphics (QD) || 100 || × 1.00  
|-
| Overall || 123 || × 1.53  
|}

=== Hardware Trivia ===
* Last '''68000-based''' Macintosh; ROM identical to SE/30 but 32-bit addressing disabled.  
* “*Seattle*” logic board codename; early EVT boards silk-screened “LittleFish”.  
* Easter egg: type '''`G 40E053`''' in MacsBug to reveal the original compact-Mac developers list.

[[Category:Apple Vintage Computers]]
{{Navbox-AppleVintage}}