Computers organization & Assembly Language Chapter 0 INTRODUCTION TO COMPUTING Basic Concepts

Introduction to Computing Numbering and Coding Systems. Inside the Computer. Brief History of the CPU. Computers organization & Assembly Language 2

Some Important Terminology How much memory? a bit is a binary digit that can have the value 0 or 1. A byte is defined as 8 bits. A nibble is half a byte, or 4 bits. A word is two bytes, or 16 bits. A kilobyte (K) is 2 10 bytes, which is 1024 bytes. A megabyte (meg) is 2 20 bytes or 1024 K. A gigabyte is 2 30 bytes or 1024 meg. A terabyte is 2 40 bytes or 1024 gig. 3 Computers organization & Assembly Language

Inside the Computer Two types of memory used in microcomputers are RAM and ROM. RAM –RAM stands for random access memory (called read/write memory). –RAM is used by the computer for temporary storage of programs that it is running. –RAM is sometimes called volatile memory. ROM –ROM stands for read-only memory. It contains programs and information essential to operation of the computer. –It is called nonvolatile memory. 4 Computers organization & Assembly Language

Inside the Computer Cache – A very fast type of RAM that is used to store information that is most frequently or recently used by the computer –Recent computers have 2-levels of cache; the first level is faster but smaller in size (usually called internal cache), and the second level is slower but larger in size (external cache). Introduction to Microprocessors & Assembly Language 5

Typical Memory Hierarchy Introduction to Microprocessors & Assembly Language 6 Microprocessor Registers L1 Cache L2 Cache Memory Disk, Tape, etc Memory Bus I/O Bus Faster Bigger

Memory Ordered sequence of bytes – –The sequence number is called the memory address Byte addressable memory – –Each byte has a unique address – –Supported by almost all processors Physical address space – –Determined by the address bus width – –Pentium has a 32-bit address bus Physical address space = 4GB = 2 32 bytes – –Itanium with a 64-bit address bus can support Up to 2 64 bytes of physical address space

Address Space Address Space is the set of memory locations (bytes) that can be addressed

The Need for a Memory Hierarchy Widening (expand) speed gap between CPU and main memory – –Processor operation takes less than 1 ns – –Main memory requires more than 50 ns to access Each instruction involves at least one memory access – –One memory access to fetch the instruction – –Additional memory accesses for instructions involving memory data access Memory bandwidth limits the instruction execution rate Cache memory can help bridge the CPU-memory gap Cache memory is small in size but fast

Internal organization of computers 10 Computers organization & Assembly Language

Internal organization of computers CPU (Central Processing Unit). Its function is to execute (process) information stored in memory. I/O (Input/Output) Devices. They provide a means of communicating with the CPU. A Bus is a common group of wires that interconnect components in a computer system. The buses that interconnect the sections of a computer system transfer address, data, and control information between the microprocessor and its memory and I/O systems. 11 Computers organization & Assembly Language

Internal organization of computers The address bus requests a memory location from the memory or an I/O location from the I/O devices. If I/O is addressed, the address bus contains a 16-bit I/O address from 0000H through FFFFH. The data bus transfers information between the microprocessor and its memory and I/O address space. Data transfers vary in size, from 8 bits wide to 64 bits wide in various members of the Intel microprocessor family. The control bus contains lines that select the memory or I/O and cause them to perform a read or write operation. 12 Computers organization & Assembly Language

CPU Memory Interface Address Bus – –Memory address is put on address bus – –If memory address = m bits then 2 m locations are addressed Data Bus: b-bit bi-directional bus – –Data can be transferred in both directions on the data bus – –Note that b is not necessary equal to w or s. So data transfers might take more than a single cycle (if w > b). Control Bus – –Signals control transfer of data – –Read request – –Write request – –Complete transfer

Brief History of the CPU The heart of the computer system is the microprocessor integrated circuit. The microprocessor, sometimes referred to as the CPU is the controlling element in a computer system. The microprocessor controls memory and I/O through a series of connections called buses. The microprocessor performs three main tasks for the computer system: 1.data transfer between itself and the memory or I/O systems. 2.simple arithmetic and logic operations. 3.program flow via simple decisions. Albeit these are simple tasks, but through them, the microprocessor performs virtually any series of operations or tasks. 14 Computers organization & Assembly Language

 Processor consists of  Datapath  ALU  Registers  Control unit  ALU  Performs arithmetic and logic instructions  Control unit (CU)  Generates the control signals required to execute instructions  Implementation varies from one processor to another Processor (CPU)

Brief History of the CPU 8080: The world’s first 8-bit general-purpose microprocessor. 8086: A far more powerful, 16-bit machine : This extension of the 8086 with memory 16-MByte : Intel’s first 32-bit machine, 80486: Full cache technology and sophisticated instruction pipelining. Pentium: Intel introduced the use of superscalar tech­niques. Pentium Pro: Move into superscalar organization. Pentium II: The Pentium II incorporated Intel MMX technology. Pentium III: Additional FP instructions to support 3D graphics. Pentium 4: Additional FP and other en­hancements for multimedia. Itanium: This new generation of Intel processor makes use of a 64-bit organi­zation with the IA-64 architecture. 16 Computers organization & Assembly Language

Brief History of the CPU 17 Computers organization & Assembly Language

CISC and RISC CISC refers to Complex Instruction Set Computer. CISC key features: –Large and complex instruction set –Large instruction sets –More addressing modes –Variable width instructions –Requires microcode interpreter Each instruction is decoded into a sequence of micro-operations –Example: Intel x86 family 18 Computers organization & Assembly Language

CISC and RISC RISC refers to Reduced Instruction Set Computer RISC Key features: –Large number of general purpose registers –Small and simple instruction set –All instructions have the same width –Simpler instruction formats and addressing modes –Decoded and executed directly by hardware –Examples: ARM, MIPS, PowerPC, SPARC, etc. Introduction to Microprocessors & Assembly Language 19

20 The End Computers organization & Assembly Language