Course Text

For reference - acronyms

Computing Abstractions and Technology. Main topics are:

The Industry

Software/Hardware symbiosis

Layers of an Architecture

The HLL abstracts away from details of the underlying hardware and allows the same program to be compiled for different processors


The user is not interested in this detail, just the data as a part of some other abstraction. That abstraction is a file, a unit of sequential data which is catalogued with various attributes and identified by a name.

e.g. http:// cs-alb-pc3/ is a file name which is globally accessible over the internet, but it is stored as a sequence of blocks of data on a disc drive in my office.

Architectural abstraction

This is the interface between the software and the hardware allows for varying hardware implementations (for example at different cost and performance) of the same machine such that they run identical code.

Instruction Set Architecture


the component that sequesces various stages of the instruction's execution, e.g. read register, perform operation, write back result

Structure of each Component

Memory hierarchy

Technological Trends

The integrated circuit was invented less than 40 years ago (the integration of one transistor and several passive components was demonstrated in 1959)

Since then the number of components integrated has increased about 100 million times and the speed of the circuits about 10 thousand times.

IC fabrication

CMOS is the most common IC fabrication process. This uses both n- and p-type metal(conductor)-oxide-semiconductor transistors. The advantages are:

IC fabrication - a Printing process

Wafers of silicon some 2 mm in thickness and some 20 cm in diameter are the "pages" that are printed by the IC fabrication process.

patterns are printed in photosensitive chemicals which when etched, selectively control the action of further chemical processes

Wafers and Dies, Cost and Yield

This Yield (i.e. the percentage of working die on a wafer) limits the complexity of the chips that can be fabricated in a given process

IC Market Trends

Semiconductor Market Growth

This figure shows the growth of the semi-conductor market and shows trends for all components and microcomputer components. The latter has a compound annual growth rate (CAGR) of 27% between 1989 and 1994 and a forecast CAGR of 20% between 1994-1995. The market shows very few signs of leveling off. But then if this did occur the tremendous investments required would no longer be possible. It is these increasing investments with each new fabrication process that enable the continual reduction of feature size, which in turn gives the combined advances of density and speed that we have come to expect.

As an aside the microprocessor you perform your word processing on is probably as powerful as the mainframe used to conduct the entire business of large corporations less than a decade ago.

Minimum feature size

This graph shows feature size against year of manufacture and is based on Intels production lines through to 1995 and beyond represents the projection (Silicon roadmap) produced by the Semiconductor Industry Association.

In less than 40 years the feature size has shrunk by two orders of magnitude. Microprocessor die size has also increased 60 times between 1970 and 1995. Circuit density of course increases inversely proportional to feature size squared and proportional to die size, giving nearly 6 orders of magnitude increase over that period.

Microprocessor Development Cost by Generation

This diagram illustrates the development cost for each new generation of Intel microprocessor normalised to the cost of developing the intel 8080.

It is interesting to note the market cost at the value added end of the market chain. taking three generations of microprocessor and looking at similar configuration PCs we have:

        Year   Cost $   Cost per MIPS $ 
        1991    6199         225 
  Early 1994    2799         52 
    Mid 1995    1399         11

Pins per Chip

This scatter plot gives an indication of the number of pins used on a variety of microprocessor packages. These have increased from 64 in 1978 to over 500 in current state-of-the-art microprocessors. For example the DEC alpha 21164 and UltraSparc. During this period data bus widths have increased from 8 bits to 128 bits and address bus widths from 16bits to 40bits (Alpha 21164). It should be noted that an increasing number of pins are also required for power and ground in order to keep supplies stable over such large area dies.

This diagram is indicative of one of the major problems facing computer architects, the growing gap between processing power on chip (measured in gatehertz) and the I/O bandwidth off chip, measured in pinhertz.

Mips per Pin