Fundamentals of Quantitative Design and Analysis - Computer Architecture: A Quantitative Approach - page 16

To plan for the evolution of a computer, the designer must be aware of rapid changes in im-
plementation technology. Five implementation technologies, which change at a dramatic pace,
are critical to modern implementations:
■ Integrated circuit logic technology —Transistor density increases by about 35% per year, quad-
rupling somewhat over four years. Increases in die size are less predictable and slower,
ranging from 10% to 20% per year. The combined effect is a growth rate in transistor count
on a chip of about 40% to 55% per year, or doubling every 18 to 24 months. This trend is
popularly known as Moore's law. Device speed scales more slowly, as we discuss below.
■ Semiconductor DRAM (dynamic random-access memory)—Now that most DRAM chips are
primarily shipped in DIMM modules, it is harder to track chip capacity, as DRAM manu-
facturers typically offer several capacity products at the same time to match DIMM capa-
city. Capacity per DRAM chip has increased by about 25% to 40% per year recently, doub-
ling roughly every two to three years. This technology is the foundation of main memory,
and we discuss it in Chapter 2 . Note that the rate of improvement has continued to slow
over the editions of this topic, as Figure 1.8 shows. There is even concern as whether the
growth rate will stop in the middle of this decade due to the increasing difficulty of ei-
ciently manufacturing even smaller DRAM cells [Kim 2005]. Chapter 2 mentions several
other technologies that may replace DRAM if it hits a capacity wall.
FIGURE 1.8 Change in rate of improvement in DRAM capacity over time . The first two
editions even called this rate the DRAM Growth Rule of Thumb, since it had been so depend-
able since 1977 with the 16-kilobit DRAM through 1996 with the 64-megabit DRAM. Today,
some question whether DRAM capacity can improve at all in 5 to 7 years, due to difficulties in
manufacturing an increasingly three-dimensional DRAM cell [Kim 2005].
■ Semiconductor Flash (electrically erasable programmable read-only memory)—This non-
volatile semiconductor memory is the standard storage device in PMDs, and its rapidly
increasing popularity has fueled its rapid growth rate in capacity. Capacity per Flash chip
has increased by about 50% to 60% per year recently, doubling roughly every two years.
In 2011, Flash memory is 15 to 20 times cheaper per bit than DRAM. Chapter 2 describes
Flash memory.
■ Magnetic disk technology —Prior to 1990, density increased by about 30% per year, doubling
in three years. It rose to 60% per year thereafter, and increased to 100% per year in 1996.
Since 2004, it has dropped back to about 40% per year, or doubled every three years. Disks
are 15 to 25 times cheaper per bit than Flash. Given the slowed growth rate of DRAM, disks