Secondary Memory

MEMORY HIERARCHIES
     As you go down the list, access time increases and price decreases.

1. CPU Registers
2. Cache
3. Main Memory
4. Magnetic Disk
5. Tape / Optical Disk

DISKS

• MAGNETIC
• FLOPPY
• IDE
• SCSI

RAID

CD-ROMS

• RECORDABLES
• REWRITABLES

DVDS

• "Digital (Video/Versatile) Disk"
• Uses Red Laser
• Smaller Pits than CDs
• Tighter spiral than CDs
• 4.7 GB for single side, single layer
• Dual Layer - reflective + semi-reflective layer
• Focus laser for different content
• 1.4 MB/sec... meh...
• Hollywood --> incompatible US and EUR DVDS 
• Can't buy and watch new movie before it has come out

BLU-RAYS

• Blue Laser (not Red like DVD)
• Shorter Wavelength
• Focuses Easier
• Allows for more Pits and Lands
• Stores up to 25 GIGABYTES on ONE SIDE!!
• Data Rate 4.5 MB/sec 
• Magnetic disk has better rate (100 MB/sec)