various Technology Trends in Computer Industry

Technology Trends

The changes in the computer applications space over the last decade have dramatically changed the metrics. Desktop computers remain focused on optimizing cost-performance as measured by a single user, servers focus on availability, scalability, and throughput cost-performance, and embedded computers are driven by price and often power issues.

If an instruction set architecture is to be successful, it must be designed to survive rapid changes in computer technology. An architect must plan for technology changes that can increase the lifetime of a computer.

The following Four implementation technologies changed the computer industry:

Integrated circuit logic technology—Transistor density increases by about 35% per year, and die size increases 10% to 20% per year. The combined effect is a growth rate in transistor count on a chip of about 55% per year.

Semiconductor DRAM : Density increases by between 40% and 60% per year and Cycle time has improved very slowly, decreasing by about one-third in 10 years. Bandwidth per chip increases about twice as fast as latency decreases. In addition, changes to the DRAM interface have also improved the bandwidth.

Magnetic disk technology: it is improving more than 100% per year. Prior to 1990, density increased by about 30% per year, doubling in three years. It appears that disk technology will continue the faster density growth rate for some time to come. Access time has improved by one-third in 10 years.

Network technology—Network performance depends both on the performance of switches and on the performance of the transmission system, both latency and bandwidth can be improved, though recently bandwidth has been the primary focus. For many years, networking technology appeared to improve slowly: for example, it took about 10 years for Ethernet technology to move from 10 Mb to 100 Mb. The increased importance of networking has led to a faster rate of progress with 1 Gb Ethernet becoming available about five years after 100 Mb.

These rapidly changing technologies impact the design of a microprocessor that may, with speed and technology enhancements, have a lifetime of five or more years.

Scaling of Transistor Performance, Wires, and Power in Integrated Circuits

Integrated circuit processes are characterized by the feature size, which is decreased from 10 microns in 1971 to 0.18 microns in 2001. Since a transistor is a 2-dimensional object, the density of transistors increases quadratically with a linear decrease in feature size. The increase in transistor performance, this combination of scaling factors leads to a complex interrelationship between transistor performance and process feature size.

First approximation, transistor performance improves linearly with decreasing feature size.

In the early days of microprocessors, the higher rate of improvement in density was used to quickly move from 4-bit, to 8bit, to 16-bit, to 32-bit microprocessors. More recently, density improvements have supported the introduction of 64-bit microprocessors as well as many of the innovations in pipelining and caches.

The signal delay for a wire increases in proportion to the product of its resistance and capacitance. As feature size shrinks wires get shorter, but the resistance and capacitance per unit length gets worse. Since both resistance and capacitance depend on detailed aspects of the process, the geometry of a wire, the loading on a wire, and even the adjacency to other structures. In the past few years, wire delay has become a major design limitation for large integrated circuits and is often more critical than transistor switching delay. Larger and larger fractions of the clock cycle have been consumed by the propagation delay of signals on wires. In 2001, the Pentium 4 broke new ground by allocating two stages of its 20+ stage pipeline just for propagating signals across the chip.

Power also provides challenges as devices are scaled. For modern CMOS microprocessors, the dominant energy consumption is in switching transistors. The energy required per transistor is proportional to the product of the load capacitance of the transistor, the frequency of switching, and the square of the voltage. As we move from one process to the next, the increase in the number of transistors switching and the frequency with which they switch, dominates the decrease in load capacitance and voltage, leading to an overall growth in power consumption.