C H A P T E R 1
This chapter describes the general architecture of the Newton system software,
which is divided into three levels, as shown in Figure 1-1 (page 1-2).
The lowest level includes the operating system and the low-level communications
system. These parts of the system interact directly with the hardware and perform
basic operations such as memory management, input and output, and task switching.
NewtonScript applications have no direct access to system services at this level.
The middle level consists of system services that NewtonScript applications can
directly access and interact with to accomplish tasks. The system provides
hundreds of routines that applications can use to take advantage of these services.
At the highest level are components that applications can use to construct their user
interfaces. These reusable components neatly package commonly needed user
interface objects such as buttons, lists, tables, input fields, and so on. These
components incorporate NewtonScript code that makes use of the system services
in the middle level, and that an application can override to customize an object.
The Newton platform incorporates a sophisticated preemptive, multitasking
operating system. The operating system is a modular set of tasks performing
functions such as memory management, task management, scheduling, task to task
communications, input and output, power management, and other low-level
functions. The operating system manages and interacts directly with the hardware.
A significant part of the operating system is concerned with low-level communication
functions. The communication subsystem runs as a separate task. It manages the
hardware communication resources available in the system. These include serial,
fax modem, AppleTalk networking, and infrared. The communication architecture
is extensible, and new communication protocols can be installed and removed at
run time, to support additional services and external devices that may be added.