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

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

Review Hardware Today’s computers

Outline Today’s computers I/O systems

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

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

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

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

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)

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

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

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

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

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

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

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

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

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