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Chapter 1
Hardware Overview
The NEC Advanced Personal Computer (APC) has two basic components: a Main
Unit and a Keyboard. The Keyboard, which cable-connects to the Main Unit, is
common to all APC models. The Main Unit, which houses the Central Processing
Unit (CPU), memory, visual display, sound output, and peripheral controllers, is
available in three models: (I) a Monochrome Cathode Ray Tube (CRT) Display
with one 8-inch Flexible Disk Drive (FDD), (2) a Monochrome CRT Display with
two 8-inch FDDs, and
(3)
a Color CRT Display with two 8-inch FDDs. Several
options and accessories are available to enhance performance or to adapt the APC
for special applications.
Figure 1-1 is a block diagram of the APe. The Main Unit, the heart of the APC, has
a CRT Display, one or two 8-inch FDDs, an ON/OFF switch, and several controls
associated with the CRT Display. Three Input/Output (I/O) cable connectors are
available at the rear of the cabinet.
The CPU, memory, and basic control logic are contained in the Main Unit on two
quad-layered Printed Circuit Boards (PCB): a Processor PCB (G9PFBU) and a
Controller PCB (G9PFCU). These PCBs plug into a mother board interface bus
that has the space and power for up to three additional (optional) PCBs.
The Processor PCB contains as standard equipment:
• A 16-bit 8086 Microprocessor
• An 8288 Bus Controller with 20-bits of addressing, making one megabyte
(MB) of memory accessible
• 128 kilobytes (KB) (standard) of Random Access Memory (RAM)
• 8 KB of Read-Only Memory (ROM)
• 4 KB of CMOS Battery-Backed Memory, which remains refreshed for at
least two years without ac power
• A 4-channel Direct Memory Access (DMA) Controller
1-1
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