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Fundamentals of Computers - Chapter 3

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Fundamentals of Computers

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Fundamentals of Computers - Chapter 3

  1. 1. © Oxford University Press 2016. All rights reserved. Fundamentals of Computers Reema Thareja
  2. 2. © Oxford University Press 2016. All rights reserved. Chapter 3 Computer Memory and Processors
  3. 3. © Oxford University Press 2016. All rights reserved. Memory is an internal storage area in the computer, which is used to store data and programs either temporarily or permanently. Introduction
  4. 4. © Oxford University Press 2016. All rights reserved. Memory Hierarchy
  5. 5. © Oxford University Press 2016. All rights reserved. • Fastest memory among all types of computer data storage • Located inside the processor, thus directly accessible by the CPU • Stores a word of data (either 32 or 64 bits) • CPU instructions instruct the ALU to perform operations on this data Processor Registers
  6. 6. © Oxford University Press 2016. All rights reserved. • An intermediate form of storage between the ultra-fast processor registers and RAM • Stores instructions and data that are repeatedly required to execute programs • Improves the overall system speed, thereby increasing the performance of the computer Cache Memory
  7. 7. © Oxford University Press 2016. All rights reserved. • Directly accessed by the CPU • Any data that has to be operated by the CPU is stored in this memory • There are two types: Random Access Memory (RAM) Read Only Memory (ROM) Primary Memory
  8. 8. © Oxford University Press 2016. All rights reserved. • A volatile storage area that is used to store data temporarily, so that it can be promptly accessed by the processor • Called “random access” because any memory cell can be directly accessed if its address is known • There are two types: Static RAM Dynamic RAM Random Access Memory (RAM)
  9. 9. © Oxford University Press 2016. All rights reserved. • Holds data without an external refresh as long as it is powered • Made of D flip-flops • No need for an external refresh process to be carried out • SRAM is faster and more reliable than DRAM • Occupies more space and is more expensive than DRAM Static RAM (SRAM)
  10. 10. © Oxford University Press 2016. All rights reserved. • A DRAM chip contains millions of tiny memory cells • To store a bit of information in a DRAM chip, a tiny amount of power is put into the cell to charge the capacitor • A refresh process is required to maintain the charge in the capacitor so that it can retain the information • One disadvantage of DRAM is that the capacitor leaks energy very quickly and can hold the charge for only a fraction of a second Dynamic RAM (DRAM)
  11. 11. © Oxford University Press 2016. All rights reserved. • A non-volatile memory that retains the data even after the power is switched off • Refers to computer memory chips containing permanent or semi- permanent data • A small amount of ROM stores critical programs such as BIOS Read Only Memory (ROM)
  12. 12. © Oxford University Press 2016. All rights reserved. • Programmable ROM (PROM) can be written to or programmed using a special device called a PROM programmer which uses high voltages to permanently write data in it • Erasable Programmable ROM (EPROM) can be erased and re- programmed by exposing the chip to strong UV light and then rewriting at a higher voltage • Electrically Erasable Programmable PROM (EEPROM) allows contents to be electrically erased and then rewritten Types of ROM
  13. 13. © Oxford University Press 2016. All rights reserved. • Also known as external memory or auxiliary storage • Not directly accessible by the CPU • Holds data even after the power is switched off • Cheaper than primary memory and can be used to store large amounts of data Secondary Storage Devices
  14. 14. © Oxford University Press 2016. All rights reserved. • Mass storage devices capable of backing up and retaining large volumes of data • Used as sequential access secondary storage devices • Data is stored in form of records • Cheap, compact in size, light in weight, can store large amounts of data and use less power • Slow, can be used sequentially, easily susceptible to degradation due to heat, humidity, etc. Magnetic Tapes
  15. 15. © Oxford University Press 2016. All rights reserved. • Consist of thin magnetic storage medium encased in a square plastic shell lined with fabric that removes dust particles • Widely used from mid-1970s to 2000 • Inexpensive but slow and with limited storage capacity • Data can be lost if the disk is bended, removed, while in use, or exposed to excessive temperature, dust, or smoke Floppy Disks
  16. 16. © Oxford University Press 2016. All rights reserved. • A set of disks, stacked together • Each platter requires two R/W heads, one for each side • Data is stored on the surface of a platter in sectors and tracks • The performance of a hard disk depends on its access time, which is the time required to read or write on the disk • Enable random access of data • Can be used as a shared device in time-sharing environment • Larger in size and heavier in weight as compared to flash drives and optical disks Hard Disks
  17. 17. © Oxford University Press 2016. All rights reserved. • Optical storage refers to storing data on an optically readable medium by making marks in a pattern that can be read using a beam of laser light precisely focused on a spinning disk • Most widely used and reliable storage devices • Popular optical storage devices are:  CD-ROM  DVD-ROM  CD-Recordable  CD-Rewritable Optical Drives
  18. 18. © Oxford University Press 2016. All rights reserved. • Uses laser technology to read and write data onto the disk • A single CD-ROM can store a large amount of data, but once the information is stored on it, it becomes permanent • Storage capacity varies from 650 MB to 1 GB • CD-ROM drive is used to read the information stored in a CD- ROM CD-ROM
  19. 19. © Oxford University Press 2016. All rights reserved. • Extremely high-capacity optical disk with storage capacity from 4.7 GB to 17 GB • Widely used to store large databases, movies, music, complex software, etc. • Double-sided disks, as they can store data on both the sides of the disk DVD-ROM
  20. 20. © Oxford University Press 2016. All rights reserved. • The process of writing data on the optical disk is called burning • Can be used in any CD-ROM drive and is functionally equivalent to a pre-recorded CD-ROM • Once data is written on the CD-R, it cannot be changed • Users can continue to store data on other parts of the disk until it is full CD-R (Recordable)
  21. 21. © Oxford University Press 2016. All rights reserved. • Users can write and over-write data on the CD-RW disk multiple times • The reliability of the disk tends to decrease, each time data is rewritten CD-RW (Rewritable)
  22. 22. © Oxford University Press 2016. All rights reserved. • Removable, rewritable, and are physically much smaller drives, weighing less than 30 g • Data is impervious to damages due to scratches and dust • Very robust, portable with high data capacity • Use very little power • No need to install device drivers • Can sustain only a limited number of write and erase cycles • Cost per unit of storage of a flash drive is higher USB Flash Drives
  23. 23. © Oxford University Press 2016. All rights reserved. • A small device that can store digital files • Easily portable, smaller, require less power • Have higher storage capacity, are completely silent, are less prone to mechanical failures, allow immediate access to data Memory Cards
  24. 24. © Oxford University Press 2016. All rights reserved. • Mass storage refers to storing enormous amounts of data in a persistent manner • Mass storage devices can store up to several trillion bytes of data • Have high data storage capacity, are easily portable, and have low power consumption • Commonly used devices are:  Disk Array  Automated Tape Library  CD-ROM Jukebox Mass Storage Devices
  25. 25. © Oxford University Press 2016. All rights reserved. • Commonly known as a redundant array of independent disks (RAID) • Group of one or more physically independent and high-capacity hard disk drives • Used in place of larger, single disk drive systems • Improve speed and increase protection against loss of data Disk Array
  26. 26. © Oxford University Press 2016. All rights reserved. • One or more tape drives to store large amounts of data ranging from 20 terabytes to more than 411 petabytes • A cost-effective solution to the problem of storing large volumes of data Automated Tape Library
  27. 27. © Oxford University Press 2016. All rights reserved. • Also known as an optical jukebox, an optical disk library, or a robotic drive • Data storage device that can automatically load and unload optical disks to provide terabytes and petabytes of tertiary storage • Can have up to 2,000 slots for disks and usually have a robot that traverses the slots and drives for loading the appropriate CD-ROM CD-ROM Jukebox
  28. 28. © Oxford University Press 2016. All rights reserved. Basic Processor Architecture
  29. 29. © Oxford University Press 2016. All rights reserved. • A computer memory that provides quick access to the data currently being used for processing • ALU stores all temporary and final results in registers • No. of general purpose registers varies from processor to processor • When program execution is complete, the result of processing is transferred from accumulator to the memory through MBR Registers
  30. 30. © Oxford University Press 2016. All rights reserved. • MAR stores the address of the data or instruction to be fetched from the main memory • MBR stores the data or instruction fetched from the memory • IR stores the instructions currently being executed • I/O register is used to transfer data or instructions to or from an I/O device • PC stores the address of the next instruction to be executed Registers
  31. 31. © Oxford University Press 2016. All rights reserved. • To execute an instruction, a processor follows a set of basic operations that are together called Instruction Cycle • Fetch: Retrieving an instruction or a data from memory • Decode: Interpreting the instruction • Execute: Running the corresponding commands to process data • Store: Writing the results of processing into memory Instruction Cycle
  32. 32. © Oxford University Press 2016. All rights reserved. Bus Interface
  33. 33. © Oxford University Press 2016. All rights reserved. • Provides functions for transferring data between the execution unit of the CPU and other components of the computer system that lie outside the CPU • Puts the contents of the program counter on address bus • Once the memory receives an address from the BIU, it places the contents at that address on the data bus, which is then transferred to the IR of the processor through the MBR Bus Interface
  34. 34. © Oxford University Press 2016. All rights reserved. Instruction Set • Set of commands that instructs the processor to perform specific tasks • For example, tells the processor what it needs to do, from where to find the data, from where to find instruction, etc. • Can be built into the hardware, or can be emulated in the software using an interpreter
  35. 35. © Oxford University Press 2016. All rights reserved. • Controls the timing of all operations within the computer • Synchronize various operations that take place within computer • Measured by the number of ticks per second • A processor can perform some operations in a single clock tick • Faster the clock ticks, more is the number of operations that can be performed System Clock
  36. 36. © Oxford University Press 2016. All rights reserved. • Pipelining is a technique with which the processor can fetch the second instruction before completing the execution of the first instruction • Such processors that can execute more than one instruction per clock cycle are called superscalar processors • With superscalar architecture, processors can execute programs faster by replicating components such as ALUs Pipelining
  37. 37. © Oxford University Press 2016. All rights reserved. • In parallel processing, multiple processors can be used simultaneously to execute a single program or task • A complex and large task is divided into smaller tasks in such a way that each task can be allocated to a processor Parallel Processing
  38. 38. © Oxford University Press 2016. All rights reserved. • In CISC, hardware bear more responsibility than the software so that the software can be simple and easy • Programs can be very simple and short requiring less space • Less effort is required by the translator to convert the program into machine language, thus faster execution • However, machines require additional hardware circuitry CISC Computers
  39. 39. © Oxford University Press 2016. All rights reserved. • RISC utilizes a small but highly optimized set of instructions • Although RISC machines are less complex and less expensive, they place extra demand on programmers to implement complex computations by combining simple instructions RISC Computers

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