Computer Hardware Processing and Internal Memory

Secondary Storage Input Output Processing Internal Memory

CPU - Central Processing Unit u Parts of the CPU l CU - Control Unit l ALU - Arithmetic/Logic Unit l registers l internal bus u Also referred to as the microprocessor

Control Unit u part of the CPU that coordinates the operation of the computer u manages the flow of data u converts instructions into commands that the computer can understand

Arithmetic Logic Unit u Performs the actual processing by performing arithmetic and logic operations on the data

Registers u special high speed storage locations within the CPU l instruction register l address register l storage register l accumulator

Memory (RAM) u The section of the computer that holds: l data and program instructions awaiting processing l intermediate processing results l processed output

Processing u All program instructions are converted to binary instructions called machine language. u The processing of a single machine language instruction is accomplished in a four step machine cycle u The system clock synchronizes the machine cycle l measured in Megahertz (MHz) l 1 MHz is 1 million clock cycles per second

Machine Cycle

u Instruction cycle (I-cycle) l The control unit fetches from memory the next command to be executed. The control unit d e c o d e s the command into an instruction that the ALU can process. CU u Execution cycle (E-cycle) l The control unit retrieves the needed data from memory and commands the ALU to e x e c u t e the required instruction l The control unit stores the result in memory.

The System Unit

Memory u types of internal memory l RAM - Random Access Memory l Cache Memory l ROM - Read Only Memory

Random Access Memory (Main Memory) u used to store programs and data on which the computer is currently working u measured in megabytes on PC’s u volatile memory u SIMM, DIMM u DRAM, SDRAM

Cache Memory u A storage area, where the computer stores the most recently accessed data. u external cache u internal cache l level 2 cache (L2 cache) u SRAM

Read Only Memory u a software-in-hardware module that can be read but not written on u nonvolatile memory u important pieces of system software are stored in ROM

System Bus u Communication system for the computer u a set of wires etched into the system board (motherboard)

Types of System Buses u internal bus - on the microprocessor u data bus - links the CPU to RAM u expansion bus - extends the data bus to establish links with peripherals l ISA, EISA u local bus - handle the most time critical busing operations (display, storage, network) l PCI

Copyright (c) 1998 by Harcourt Brace & Company. All rights reserved.

Add in Boards (Cards) u Customization of computer u card-like pieces of hardware that contain the circuitry to perform specific functions u Variety of brands and functions l graphics adapter l fax/modem board l sound card l network card u plug into expansion slots

Ports u sockets that allow you to plug in external hardware devices u parallel l 25 holes l printers, tape drives u serial (com ports) l 9 or 25 pins l connects low speed peripherals such as scanners and external modems l Universal Serial Bus (USB) u mouse port, keyboard port

Increasing Computer Speed u increase clock speed u increase word size u add cache, more RAM u packing circuits closer together u symmetric multiprocessing u RISC architecture u pipelining instructions

Pipelining Instructions

PC Microprocessors u 8088 and 8086 u u SX and DX u or i486 SX and DX u Intel’s Pentium, Pentium Pro, Pentium II, Celeron, Pentium III, Pentium III Xeon l MMX u Cyrix, AMD u DEC Alpha