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PCs and the microprocessor chips used in them are described below.
PCs were first introduced in mid-1970s, and all PCs built during the 1970s were 8bit systems. That is, they were built using microprocessor chips that could operate
on 8 bits of data at a time. Some popular microprocessor chips of this type are
Zilog's Z80, MOS Technology's 6502, Intel's 8080, and Motorola's 6809. All these
microprocessor chips have built-in eight-line data buses. This means that these
chips can only retrieve from storage, manipulate, and process a single 8-bit byte of
data at a time. They are thus 8/8 bit chips. A 16-line address bus is also built into
these chips to determine the primary storage locations of the instructions and data
that are needed. With 16 address lines, a maximum of 64 Kilobytes (2 16) or 65,536
separate storage locations can be identified by these chips. Some of the PCs that
were built by using these types of microprocessor chips are Apple II, Commodore
64, and Radio Shack TRS-80 systems.
In early 1980s, microprocessor suppliers introduced 16-bit microprocessor chips
that could operate on 16 bits of data at a time. Intel 8088 is the most popular
microprocessor chip of this type. The original IBM PC, the IBM PC/XT, and most
of the IBM compatible PCs (PCs manufactured using IBM’s specifications)
manufactured during 1984 and later, used the Intel 8088 microprocessor chip. In
the 8088 chip, although the internal data path between the CPU and its associated
registers is 16 bits wide, the external data path between the CPU and primary
storage is only 8 bits wide, and so all operations to and from storage are done 8
bits (1 byte) at a time. Once received, however, data are processed 16 bits at a time internally in the 8088 chip. The 8088 is thus an 8/16 bit chip. An extension of the
8088 chip is Intel's 8086 chip. Unlike the 8088, both the internal and external data
paths of the 8086 chip are 16 bits wide. Ther8Q86 is4hus a true 16/16-bit chip.
With an expanded built-in address bus having 20 lines, both the 8088 and the 8086
chips can identify a maximum of 1 Megabyte (2 20) or 1,048,576 separate stor...
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This document was uploaded on 04/07/2014.
- Spring '14