Data Models

This document outlines key data structures and memory models used in System 7.1.

Memory Models

The Heap

Memory is divided into heaps.

• System Heap: Persistent memory for OS and Drivers.
• Application Heap: Volatile memory for the currently running application.

Data Types:

• Ptr: A direct pointer to a block of memory.
• Handle: A pointer to a master pointer. Allows the Memory Manager to move the underlying block (relocate it) to reduce fragmentation without invalidating references.

Resources

Data is often stored in the Resource Fork of a file.

• Map: Index of resources in the file.
• Data: The actual binary data.
• Types: 4-character codes (e.g., 'CODE', 'DLOG', 'WIND').

Core Entities

WindowRecord (WindowPtr)

Represents a window on the screen.

• port: The graphics port (GrafPort) for drawing.
• windowKind: Type of window (dialog, desk accessory, etc.).
• visible: Boolean visibility flag.
• refCon: Arbitrary data storage for the application.

DialogRecord (DialogPtr)

Extends WindowRecord for dialog boxes.

• items: Handle to the item list (controls, text).
• textH: Handle to the current text edit record.

EventRecord

Represents a user or system event.

• what: Event type (mouseDown, keyDown, updateEvt).
• message: Event-specific data (key code, window pointer).
• when: Timestamp (ticks since boot).
• where: Mouse coordinates.
• modifiers: State of Shift, Cmd, Option keys.

File System Catalog

• CatNode: A node in the HFS B-Tree (File or Folder).
• FInfo: File metadata (Type, Creator, location).

Schema Diagram (Conceptual)

classDiagram
    class EventRecord {
        +int what
        +long message
        +long when
        +Point where
        +int modifiers
    }

    class WindowRecord {
        +GrafPort port
        +short windowKind
        +boolean visible
        +boolean hilited
        +long refCon
    }

    class DialogRecord {
        +WindowRecord window
        +Handle items
        +TEHandle textH
    }

    class FileInfo {
        +OSType fdType
        +OSType fdCreator
        +short fdFlags
        +Point fdLocation
    }

    DialogRecord --|> WindowRecord : Extends
    EventRecord ..> WindowRecord : References