Riyadh Philanthropic Society For Science Prince Sultan College For Woman Dept. of Computer & Information Sciences CS 251 Introduction to Computer Organization & Assembly Language Lecture 8 (Computer System Organization) Secondary Memory

 From lecture notes  Memory Hierarchy  Floppy Disks  Magnetic Disks  RAID  Optical Disks Secondary Memory2

 No matter how big is the main memory, it will always be way too small  The categorization of the memory devices is done based on the following criteria 1.Speed 2.Size 3.Cost 4.Volatility 5.Proximity to the CPU 6.Ease of extensibility  A hierarchy is used to show this organization 3

Secondary Memory  Going up through the hierarchy, the devices are:  Faster  Smaller  More expensive  More volatile  Closer to the CPU  Least easy to extend 4 TapeOptical disk Magnetic disk Main Memory Cache Registers

Secondary Memory  Most desktop microcomputer systems have floppy disks, hard disks/ magnetic disks, and optical disk drives. 5

Secondary Memory  Diskette – Floppies - Portable storage media  Floppy disk drive (FDD)  Use flat circular pieces of Mylar plastic that is coated with magnetic material  Store data by altering the electro magnetic 6

Secondary Memory  Uses thicker metallic platters with magnetizing coating for storage  For internal hard disks  They are located inside the system unit  Known as fixed drive  Designated as the C drive  advantages over the Floppy in terms of access speed and capacity 7

Secondary Memory  Hard disks have tracks (complete circle), and sectors(part of the circle).  Head is used to read/write data on the hard disk 8

Secondary Memory  RAID (Redundant Array of Independent Disks)  Many disks that look as one disk to the operating system  They have better performance and better reliability  Data are distributed over the drive  Allows for parallel execution 9

Secondary Memory  Several schemes for distribution of the data over the disks  Known as RAID level 0 through RAID level 5  The term “level” is kind of misnomer  No hierarchy is involved  Six different organization possible, each called a level 10

Secondary Memory  Virtual single disk is divided up into strips with k sectors each  RAID 0 writes consecutive strips over the drives in round robin form  RAID Controller will break any disk command into n separate commands (one for each of the disks  Will read and write in parallel 11

Secondary Memory12 Level 2 Level 0Level 1 Level 3 Level 4

Secondary Memory  Compact  Permanent storage  Consists of Lands and pits  Laser beams reflect off pits  Two common types  CD  DVD 13

Secondary Memory  Optical Format  Capacity from 650 MB to 1 GB  Rotation speed vary  Several types  Read only: CD - ROM  Write once: CD – R  Rewritable : CD - RW 14

Secondary Memory  Also Known as Digital Video Disk  Same as the CD but with higher storage capacity  Several types  Read only: DVD - ROM  Write once: DVD+R, DVD-R  Rewritable : DVD+RW, DVD-RW, DVD-RAM 15

A Blu-ray Disc known as BD or Blu-Ray An optical disc storage medium designed to supersede the standard DVD format. Its main uses are for storing high-definition video, PlayStation 3 video games, and other data It can store up to 25 GB per single layered, and 50 GB per dual layered disc. Secondary Memory16

A USB flash drive consists of a flash memory ( type of EEPROM memory) data storage device integrated with a USB (Universal Serial Bus) interface. USB flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Storage capacities in 2010 can be as large as 256 GB with steady improvements in size and price per capacity expected. Some allow 1 million write or erase cycles and offer a 10-year shelf storage time Secondary Memory17

USB flash drives are often used for the same purposes for which floppy disks or CD-ROMs were used. They are smaller, faster, have thousands of times more capacity, and are more durable and reliable because of their lack of moving parts. USB Flash drives use the USB mass storage standard, supported natively by modern operating systems such as Linux, Mac OS X, Windows, and other Unix- like systems.LinuxMac OS XWindowsUnix- like Secondary Memory18