1. COMS 161 Introduction to Computing
Title: Computer Organization
Date: April 6, 2005
Lecture Number: 32

2. Announcements Exam 3 Wednesday, April 13 HTML Computer History
Computer Organization

3. Review
Hardware
Today’s computers

4. Outline
Today’s computers
I/O systems

5. I/O Subsystem Input/Output Secondary Storage
Exchanging data and instructions between the user and the computer
Secondary Storage
Auxiliary storage for data and instructions

6. Secondary Memory (Storage)
Backup or alternative storage in place of (volatile) RAM
Nonvolatile
Secondary memory devices (and media) are distinguished by their capacities, speed, and cost

7. Types of Memory Access Random access Direct access
Items are independently addressed
Access time is constant
Direct access
Items are independently addressed in regions
Access time is variable—though not significantly

8. Types of Memory Access Sequential access
Items are organized in sequence (linearly)
Access time is significantly variable

9. Secondary Memory Classified by the way data is organized and accessed
Sequential access storage devices and media (SASD)
Data is stored sequentially (linearly)
One item after another
All items stored before the desired item must be searched or traversed
Magnetic tape (cassette tape)

10. Secondary Memory Direct access storage devices and media (DASA)
Data is stored in regions that can be accessed directly
Device “jumps” to region where the desired item is stored
Possible small amount of traversal
Magnetic floppy disks
Magnetic hard disks
Optical discs

11. Secondary Memory Why not just use RAM?
To expensive
Volatile
Gives rise to a memory hierarchy

12. Memory Hierarchy I
Where would you put registers in this hierarchy?

13. Memory Hierarchy II
Processing hierarchy: data flows from one storage type to others

14. Types of RAM Dynamic RAM (DRAM) Main system memory
What you buy when you get more RAM
Dynamic means that the memory fades in about 1 msec
Needs to be refreshed

15. Types of RAM Synchronized Dynamic RAM (SDRAM)
Main system memory
Likely what is in your computer now
Synchronizes itself with the system clock
Double Data Rate DRAM (DDR SDRAM)
Transfers twice as much data as SDRAM

16. Types of RAM Static RAM (SRAM) Access time is four times that of DRAM
Costs more
Used where fast memory is needed
L2 cache

17. Types of RAM SIMM and DIMMs SIMM DIMM Single in-line Memory Module
Soldered onto a printed circuit board called a stick (not a memory stick)
Most SIMMS have 72 contacts
DIMM
Dual in-line memory module
Similar to SIMM’s opposite contacts are isolated

18. Direct Access Storage Devices
Magnetic hard and floppy disks
Removable hard disks
Optical discs
CD-ROM, CD-R,
WORM,
magneto-optical
GEOMETRY:
Tracks, Cylinders and Sectors