Operating System (OS) Module

The OS/ directory contains the core low-level components of Macintosh System 7.1. These components run in the kernel address space and provide essential services to the rest of the system.

Key Components

1. Memory Manager (MemoryMgr/)

Responsible for managing the system heap and application heaps.

• Concepts: Pointers, Handles (relocatable blocks), Heap Zones.
• Responsibilities: Allocation, Deallocation, Compaction, Purging.

2. Process Manager (ProcessMgr/)

Implements the cooperative multitasking model introduced in System 7.

• Responsibilities:
  • Creating and destroying processes.
  • Scheduling (context switching on WaitNextEvent).
  • Apple Events (Inter-Process Communication).

3. File System (HFS/)

Implements the Hierarchical File System (HFS).

• Features: Forks (Data Fork, Resource Fork), Catalog Tree, Extents Overflow.
• Interaction: Accessed via the File Manager API.

4. Trap Dispatcher (TrapDispatcher/)

The mechanism that intercepts m68k “A-Line” instructions (0xAxxx) and routes them to the appropriate system routine.

• Role: Provides binary compatibility and allows patching of system functions.

5. Other Managers

• TimeMgr: Manages time-based tasks and delayed execution.
• PowerMgr: Manages power states (crucial for Portables/PowerBooks).
• SlotMgr: Manages NuBus expansion slots.
• StartMgr: Handles the boot process.

Directory Structure

Directory	Description
MemoryMgr/	Memory management implementation.
ProcessMgr/	Process scheduling and IPC.
HFS/	HFS file system driver.
Traps/	Trap dispatch tables and logic.
StartMgr/	Boot logic.
MMU/	Memory Management Unit control (Virtual Memory support).

Dependencies

• Hardware: Relies heavily on m68k specific instructions and hardware mapping.
• Drivers: Uses drivers in Drivers/ to access physical storage and devices.