Hardware Reference
In-Depth Information
used the same interrupt controller as the DataMaster and a similar direct memory access (DMA)
controller. Also, expansion cards already designed for the DataMaster could easily be redesigned to
function in the PC.
The DataMaster used an Intel 8085 CPU, which had a 64KB address limit and an 8-bit internal and
external data bus. This arrangement prompted the PC design team to use the Intel 8088 CPU, which
offered a much larger (1MB) memory address limit and an internal 16-bit data bus, but only an 8-bit
external data bus. The 8-bit external data bus and similar instruction set enabled the 8088 to be easily
interfaced into the earlier DataMaster designs.
IBM brought its system from idea to delivery of functioning systems in one year by using existing
designs and purchasing as many components as possible from outside vendors. The Entry Systems
Division was granted autonomy from IBM's other divisions and could tap resources outside the
company, rather than go through the bureaucratic procedures that required exclusive use of IBM
resources. IBM contracted out the PC's languages and OS to a small company named Microsoft. That
decision was the major factor in establishing Microsoft as the dominant force in PC software.
Note
IBM had originally contacted Digital Research (the company that created CP/M, then the most
popular personal computer OS) to have it develop an OS for the new IBM PC. However,
Digital was leery of working with IBM and especially balked at the nondisclosure agreement
IBM wanted Digital to sign. Microsoft jumped on the opportunity left open by Digital Research
and, consequently, became the largest software company in the world. IBM's use of outside
vendors in developing the PC was an open invitation for the after-market to jump in and
support the system—and it did.
On August 12, 1981, a new standard was established in the microcomputer industry with the debut of
the IBM PC. Since then, hundreds of millions of PC-compatible systems have been sold, as the
original PC has grown into an enormous family of computers and peripherals. More software has
been written for this computer family than for any other system on the market.
The PC Industry 30 Years Later
In the 30 years since the original IBM PC was introduced, many changes have occurred. The IBM-
compatible computer, for example, advanced from a 4.77MHz 8088-based system to 4GHz
(4,000MHz) multicore systems that are hundreds of thousands or more times faster than the original
IBM PC (in actual processing speed, not just clock speed). The original PC had only one or two
single-sided floppy drives that stored 160KB each using DOS 1.0, whereas modern systems can have
several terabytes (trillion bytes) or more of hard disk storage.
A rule of thumb in the computer industry (called
Moore's Law
, originally set forth by Intel cofounder
Gordon Moore) is that available processor performance and disk-storage capacity doubles every one
and a half to two years, give or take.
Since the beginning of the PC industry, this pattern has held steady and, if anything, seems to be
accelerating.
Moore's Law
