Introduction
Structured Computer Organization
A computer’s native language, machine language, is difficult for human’s to use to program the computer
Due to this difficulty, computers are often structured as a series of abstractions, each building on the one below it
In this way, complexity can be mastered
This approach is called structured computer organization
Languages, Levels, and Virtual Machines
Let the machine language be called L0 (since it is at the lowest level of abstraction)
L0 is inconvenient for human use, so let’s design a new language L1 which is easier
A program written in L1 must be translated into an equivalent L0 program before it can be executed
Another possibility is to write a program in L0 that examines each individual instruction and executes the equivalent sequence of L0 instructions. This technique is called interpretation and the program is called an interpreter.
Languages, Levels, and Virtual Machines
Translation and interpretation are similar. Both methods, and a combination of the two, are widely used
Rather than think of translation/interpretation, it is often simpler to imagine a virtual machine whose machine language is L1. Call this machine M1.
Why not implement M1 directly? It might be too expensive or complicated to construct out of electrical circuits.
In order to make translation practical, M0 (the real machine) and M1 must not be too different. So, L1 might still be difficult to program! Solution? Create a new VM M2. If necessary repeat until we have a useful machine. This leads to a computer consisting of a number of layers or levels, one on top of another.
Computer as Multilevel Machine
Contemporary Multilevel Machines
Most modern computers consist of two or more levels (as many as six)
The lowest level is the digital logic level constructed from gates
Each gate has one or more digital inputs and computes some simple function of the inputs such as AND or OR. Gates are built up from transistors.
A small number of gates can be combined to form a 1-bit memory. 1-bit memories can be combined to from 16, 32, or 64 bit registers which can hold a single binary number.
Contemporary Multilevel Machines
The next level up is the microarchitecture level
At this level we see a collection of (typically) 8 to 32 registers that form a local memory and a circuit called an ALU (Arithmetic Logic Unit) capable of performing simple arithmetic operations.
The registers are connected to the ALU to form a data path over which data flow
On some machines the operation of the data path is controlled by a program called a microprogram. On other machines the data path is controlled directly by hardware.
Contemporary Multilevel Machines
Level 2 is the Instruction Set Architecture (ISA) level. This level consists of the instructions that can be carried out by the computer.
The facilities added at level 3 are carried out by an interpreter running at level 2 called an operating system. This level is called the operating system level.
Levels 4 and 5 are used by application programmers (only systems programmers use the lower three levels). The languages of levels 4 and 5 are usually translated while those of levels 2 and 3 are always interpreted.
Levels 4 and 5 provide symbolic languages while the machine languages of levels 1, 2, and 3 are numeric.
Level 4 is the assembly language level. It provides a program called an assembler which translates a symbolic form of the level 1, 2, or 3 language.
Level 5 co nsists of high-level languages such as BASIC, C, C++, and Java. Programs written in these languages are translated to level 3 or 4 languages by translators known as compilers.
A Six-Level Computer
Evolution of Multilevel Machines
The first digital computers had only two levels: the ISA level (where programming was done) and the digital logic level. The digital logic circuits were very complicated.
In 1951, Maurice Wilkes suggested the idea of a three-level computer in order to simplify the hardware. The machine was to have a built-in unchangeable program (the microprogram whose function was to execute ISA-level programs. The microprogram was easier to implement in hardware then the instruction set, so the circuits needed were simpler.
A few three-level machines were constructed in the 1950s, more during the 1960s and by 1970 microprogrammed machines were dominant.
Evolution of Multilevel Machines
Early computers were operated directly by a programmer (or a computer operator) who entered a deck of cards containing (e.g.) a FORTRAN program. The program was translated to machine language, output on cards and subsequently run.
Around 1960 people tried to reduce wasted time by automating the operator’s job. A program called an operating system was kept in the computer at all times. The programmer provided certain control cards along with the program that were read and carried out by the operating system.
Early operating systems read card decks and printed output on the line printer. These were known as batch systems. In the early 1960s timesharing systems in which users were connected to the CPU using terminals and the CPU was shared were introduced.
Due to the ease of introducing new instructions in microprogrammed architectures, by the 1970s instruction sets had grown large and the microprogram large and slow. At this point researchers realized that by simplifying the instruction set and implementing it directly in hardware the computer could be much faster.
A von Neumann Machine
First Bus-Based System
The IBM 360 Product Line
Moore’s Law
Moore’s law is name after Gordon Moore, co-founder and Chairman of Intel, who discovered it in 1965
The law states that the number of transistors that can be put on a chip doubles every 18 months
Many observers expect Moore’s law to continue to hold into the 21st Century, possibly around 2020
The Computer Spectrum
Although PCs are the most common type of computer, there are others as well
Disposable computers are found in greeting cards
Embedded computers are found inside devices such as telephones, televisions, CD players and toys
Game computers have a CPU, memory, a display and not much else (Personal Digital Assistant and Network Computers are similar)
Servers are similar to high-end PCs and may contain multiple CPUs as well as large secondary storage capabilities and high-speed networking
The Computer Spectrum
NOW (Network of Workstations) or COW (Cluster of Workstations) consist of standard PCs or workstations connected by gigabit/sec networks, and running specialized software that allow all the machines to work together on a single problem
Mainframes are large computers which have high I/O capacity and vast storage capacities
Supercomputers are typically highly parallel machines made from high-end components
Typical Prices of Computers
Pentium II
The Intel Corporation was formed in 1968.
In 1970, Intel manufactured the first single-chip CPU, the 4-bit 4004 for a Japanese company to use in an electronic calculator.
The 8088, a 16-bit CPU was chosen as the CPU for the original IBM PC.
A series of backward compatible chips (80286, 386, 486, Pentium, Pentium Pro and Pentium II) followed.
picoJava II
The Java programming language defines a Java Virtual Machine (JVM) in order to allow portability across many architectures
Usually Java programs are interpreted by a JVM interpreter written in C, but interpretation is slow.
One solution is to have a JIT (Just In Time) compiler for the machine running the JVM
Another alternative is to design hardware JVM chips, thus avoiding a level of software interpretation or JIT compilation.
Such Java chips are especially useful in embedded systems
The picoJava II is not a concrete chip, but a chip design which is the basis for a number of chips such as the Sun microJava 701 CPU.
The picoJava has two optional units: a cache and a floating-point unit which can be included or removed as the manufacturer sees fit.
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