Machine Organization

Machine Organization

Intro to Computer Architecture CR346/ECE441 Prof. Lyon How We Interact with Computers User Applications Operating System Hardware

Remember, everything is represented in bits! 2 Bits 00, 01, 10, 11 = 3 Bits 4 Bits. . 8 Bits16 Bits24 Bits- 4 values 8 values

16 values 256 Values 65,536 Values or (+/- 32,767) 16,777,216 Values What are computers made of? Primarily Transistors Invented in 1951, the Transistor is the basic electrical building block for all modern electronics

Called by many the greatest invention of the 20th century For Digital applications, transistors are packaged in what is known as Integrated Circuits (ICs) As many as 1 Billion Transistors can be packaged in a single large IC today Anatomy of a Transistor Transistors are fabricated using silicon (derived from quartz) and tiny amounts of impurities such as

selenium or gallium arsenide to create what is called a semiconductor Semiconductors allow us to control the flow of electrical charge (electrons) very precisely. Millions of semiconductors can be placed on an integrated circuit using a process called photolithography CD CD=critical dimension, target design rule

Proportional to the wavelength of illumination Transistor Functionality In various circuits Transistors can be made to: Amplify or Attenuate electrical signals Invert electrical signals Store electrical voltage values Switch electrical signals off and on Transistors can be combined to create logic circuits

commonly known as GATES Gates are packed into Integrated Circuits commonly known as Chips Simple Silicon Semiconductor Devices Intel 4004 Processor Chip circa 1971 It could only add and subtract 4 bits at a time.

AMD Athlon64 Processor 2004 Use of Logic Gates in Computers Primary Uses: Switches and logic circuits that can be switched between 0 and 5 volts. In this way a Switch can signify a bit that is a 1 or a 0 Storage of voltage levels equivalent to 0 or 5 volts. In this way a bits of memory can be

implemented or pixels on an LCD display on a laptop can be created AND and OR Gates NOT Gate By combining gates we can create useful functions such as a the ability to store a bit of information

The purpose of a latch is to allow a data value to be stored temporarily. So that we can hold it and use it for awhilelike a bit of memory John Von Neumann (19031954) Von Neumann visits the Moore School in 1944

prepares a draft for an automatic programmable device (later called EDVAC) stored program concept

publishes ideas (with Goldstine and Burks) in 1946 designed the IAS (Institute for Advanced Studies) machine which became operational in 1951 Von Neumann Architecture

stored program serial uniprocessor design binary internal encoding

CPUMemoryI/O orgranization fetch-decodeexecute instruction cycle The Von Neumann Machine

CPU = Central Processing Unit Memory A Typical PC CPU Board

Fetch, Decode, Execute Cycle Computer instructions are stored (as bits) in memory. To run a program, each instruction is: Fetched from memory. Decoded (the computer figures out what it should do based on the number). Then the instruction is executed. The speed at which this cycle occurs is determined by the system clock

Cycle Times Generally the faster your computer can get through a fetch-decode-execute cycle, the faster it will perform. Cycle times are measured in gigahertz, a billion cycles per second. PCs these days reach 3500 Megahertz or 3.5 Gigahertz (3 billion cycles/sec) Memory

Each memory unit has its own address Memory units are organized in groups of Bytes (8 bits) or Words (16, 24, 32, 64 or 128 bits) 0 1 2 3 4 ..127 million Random Access Memory The main computer memory is called RAM (Random Access Memory) It is random in that one may access any

addressable memory unit independently of any other (and thus in random order). In almost all modern machines the smallest single addressable amount of memory is one byte. Memory is measured in megabytes or gigabytes or terabytes RAM chips on a PC board DRAM

RAM allows for both reading and writing in memory. Contrast this with ROM (readonly memory). Most RAM is volatile, or dynamic. When you turn off the power, the contents of RAM is lost. Sometimes one talks about DRAM which is short for dynamic RAM). ROM Read Only Memory can only be read from

Its contents cannot be altered or written over easily This type of memory is used to hold instructions that need to always be there and always be the same For example, the initial instructions that are executed when your PC is turned on which instructs the machine to load Windows from the disk drive Registers Registers are memory locations that are used to facilitate the movement of data inside a

digital computer Registers work in conjunction with the system clock which determines the speed with which a computer fetches and executes instructions Basic Registers in a computer IR Instruction register ACC Accumulator, used as a scratchpad MDR Memory Data register

MAR - Memory Address register PC Program Counter, points to the next instruction to be fetched More about the CPU Two of many registers in the

CPU CPU Instruction Register (IR) Accumulator Memory Machine Language

Every von Neumann style CPU has its machine language, the set of instructions it knows how to execute. CIA=Complement and Increment the accumulator (PDP-8) 7404=NOP (PDP-8) Machine Instructions Such an instruction would consist of two numbers: One would be the address of the memory

unit to be accessed. The other would be the operation code of the instruction - the (somewhat arbitrary) number that refers to a unique and particular type of instruction Structure of Instructions Suppose we used 32 bits to encode a machine language instruction. 7 bits

Op code 7 bits would allow us to have 128 different op codes. 25 bits Memory address 25 bits would allow about 32 megabytes of addressable

memory. We might need to fetch more bytes if we had to address a larger range of memory Information Transfer inside the CPU Individual bits in a memory unit are transferred to the CPU in parallel (all at the same time).

This is opposed to serially (one at at time). The same goes for information transferred between registers in the CPU. A 64 bit machine can transfer 64 bits in parallel. The Memory Bottleneck In almost all of todays machines, the machine can perform dozens of instructions in the time it takes to retrieve one item from

memory. One solution is very fast memory in the CPU call cache memory. A computer will typically have 1000s of bytes of cache, as opposed to billions of bytes of RAM. Cache Memory CPU Cache

memory is on the CPU chip. Instruction Register (IR) Accumulator Cache

Memory Central Processing Unit manages the instruction-execution cycle FETCH DECODE EXECUTE coordinates the activities of other devices The CPU and Main Memory Inside the CPU

Inside the CPU memory address register Inside the CPU memory address register

memory data register Inside the CPU memory address register

program counter memory data register Inside the CPU memory address

register instruction register program counter memory data register

Inside the CPU memory address register memory data register instruction

register program counter arithmetic logic unit Inside the CPU memory address

register instruction register program counter memory data register

accumulator (work register) arithmetic logic unit Inside the CPU memory data register

memory address register accumulator (work register) instruction

register program counter system clock arithmetic logic unit

FETCH the instruction 1. address of the next instruction is transferred from PC to MAR 2. the instruction is located in memory FETCH the instruction

3. instruction is copied from memory to MDR DECODE the instruction instruction is transferred to and decoded in the IR

EXECUTE the instruction control unit sends signals to appropriate devices to cause execution of the instruction Types of Processor Operations Data Movement

Operations moving data from memory to the CPU moving data from memory to memory input and output Arithmetic and Logical Operations integer arithmetic

comparing two quantities shifting, rotating bits in a quantity testing, comparing, and converting bits Types of Processor Operations Program Control starting a program

halting a program skipping to other instructions testing data to decide whether to skip over some instructions Smaller, Cheaper, Faster! The Mantra of the Semiconductor Industry

Moores law Clock Frequency Lead microprocessors frequency doubles every 2 years 10000 2X every 2 years Frequency (Mhz)

1000 P6 100 486 10 8085

1 0.1 1970 8086 286 Pentium proc 386

8080 8008 4004 1980 1990 Year Courtesy, Intel

2000 2010 Challenges to Continuing the Trend The thickness (in atoms) between the silicon layers in transistors is getting very thin as we attempt to cram more transistors into the same amount of spaceso much so that new materials need to be developed

HEAT!! As we put more and more transistors on a chip, the ability to cool it and keep it from burning up is increasingly a problem Noise - As more transistors are packed ever more tightly together, the noise level of the circuits increases which affects reliability A New Computing Paradigm? Quantum Computing Seeks to use the spin of atomic particles to

implement binary digital systems Molecular computing Using molecules to hold electrical charges instead of using transistors Very much in preliminary research.not here yet

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