66 CHAPTER THE SYSTEM UNIT

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 6-2 Competencies Details about memory Memory Classification Bases Cache Memory Virtual Memory

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 6-3 Quiz03 Next Lecture – (Lecture #13) Contents: Chapter 4 – The System Unit Lecture Slides- #10 - #12

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 6-4 Memory Classification Bases Reading/ Writing Capability Read Only Memory Read/ Write Memory Data Access Mechanism Sequential Access Memory Random Access Memory

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 6-5 … Memory Classification Bases Volatility of Data No Data Loss without Electricity (Non-volatile Memory) Data loses without electricity (Volatile Memory) Data can be changed and be permanently saved once changed (CMOS Memory) Speed of Access Cache Memory (Very high accessing speed)

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 6-6 Memory Holding area for data, instructions, and information Types of memory chips RAM – holds programs and data ROM – fixed start-up instructions CMOS – flexible start-up instructions

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 6-7 RAM Random Access Memory Primary Memory of a computer Data and Program needs to be loaded for processing Any memory location can be accessed randomly Volatile storage Uses Cache support for increased efficiency Flash RAM – Non-volatile/ portable

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 6-8 ROM Read-only memory Firmware Cannot be changed by the user Start-up instructions, keyboard control capabilities

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 6-9 CMOS Complementary metal-oxide semiconductor Flexible and expandable Startup information Non-volatile Its contents may be updated

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved ….The Memory (More Concepts) Virtual Memory A technique used to make huge programs run on small memory size computers A huge program is divided into many portions Each portion could be adjusted inside the RAM Program is then run by loading only the needed portion from hard disk Operating System (OS-win98) is the one who is taking care of this transparently. Effect: The program runs slowly

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved … The Memory (More Concepts)

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved Memory Capacity UnitCapacity Megabyte (MB)1 billion bytes Gigabyte (GB)1 million bytes Terabyte (TB)1 trillion bytes