Hardware Reference
In-Depth Information
processing was done with programs like troff (still used for this topic). Troff occu-
pies kilobytes of memory. Modern word processors occupy many megabytes of
memory. Future ones will no doubt require gigabytes of memory. (To a first
approximation, the prefixes kilo, mega, giga, and tera mean thousand, million, bil-
lion, and trillion, respectively, but see Sec. 1.5 for details.) Software that continues
to acquire features (not unlike boats that continue to acquire barnacles) creates a
constant demand for faster processors, bigger memories, and more I/O capacity.
While the gains in transistors per chip have been dramatic over the years, the
gains in other computer technologies have been hardly less so. For example, the
IBM PC/XT was introduced in 1982 with a 10-megabyte hard disk. Thirty years
later, 1-TB hard disks are common on the PC/XT's successors. This improvement
of five orders of magnitude in 30 years represents an annual capacity increase of
nearly 50 percent. However, measuring disk improvement is trickier, since there
are other parameters besides capacity, such as data rate, seek time, and price.
Nevertheless, almost any metric will show that the price/performance ratio has in-
creased since 1982 by about 50 percent per year. These enormous gains in disk
performance, coupled with the fact that the dollar volume of disks shipped from
Silicon Valley has exceeded that of CPU chips, led Al Hoagland to suggest that the
place was named wrong: it should have been called Iron Oxide Valley (since this is
the recording medium used on disks). Slowly this trend is shifting back in favor of
silicon as silicon-based flash memories have begun to replace traditional spinning
disks in many systems.
Another area that has seen spectacular gains has been telecommunication and
networking. In less than two decades, we have gone from 300 bit/sec modems to
analog modems at 56,000 bits/sec to fiber-optic networks at 10
12
bits/sec. Fiber-
optic transatlantic telephone cables, such as TAT-12/13, cost about $700 million,
last for 10 years, and can carry 300,000 simultaneous calls, which comes to under
1 cent for a 10-minute intercontinental call. Optical communication systems run-
ning at 10
12
bits/sec over distances exceeding 100 km without amplifiers have been
proven feasible. The exponential growth of the Internet hardly needs comment
here.
Richard Hamming, a former researcher at Bell Labs, once observed that a
change of an order of magnitude in quantity causes a change in quality. Thus, a
racing car that can go 1000 km/hour in the Nevada desert is a fundamentally dif-
ferent kind of machine than a normal car that goes 100 km/hour on a highway.
Similarly, a 100-story skyscraper is not just a scaled up 10-story apartment build-
ing. And with computers, we are not talking about factors of 10, but over the
course of four decades, factors of a million.
The gains afforded by Moore's law can be used by chip vendors in several dif-
ferent ways. One way is to build increasingly powerful computers at constant
