9/24: Memory & Storage

1. 9/24: Memory & Storage • ROM • RAM • different kinds & uses inc. VRAM, SRAM • Data storage • Magnetic • Optical image courtesy of How Computers Work CD

2. ROM? RAM? • Both refer to chip-based memory hardware • (not hard drives, CD-ROMs, etc.) • ROM: Read-Only Memory • doesn’t change (much if at all) • BIOS stored here. • RAM: Random Access Memory • changes frequently • short-term memory

3. ROM: Read-Only Memory • Chips hardwired with start-up instructions • Nonvolatile memory • doesn’t change • Non-dynamic • not dependent on electrical power to store information • Necessary to start up the operating system (OS) • Has a few options: disk drive boot order, etc.

4. RAM: Random Access Memory • Synonyms: “main memory”, “primary memory”, “user memory” • Volatile memory • contents can be changed • Why “random access”? • sequential access vs. random access • analogy: cassette vs. CD • Programs, files stored here while in use. image courtesy of How Computers Work CD

5. How much RAM do you need? • Current recommendation: 192 MB total RAM for a new computer • Windows 98 uses ~ 20 MB of RAM • Windows 2000 Pro uses ~ 95 MB of RAM • McAfee Virus Scan & Task Manager ~ 7 MB • MS Word uses ~ 7 MB • MS Internet Explorer uses ~ 7 MB • Each file you open is held in RAM, even after you close it

6. Varieties of RAM: DRAM • DRAM: Dynamic RAM • dynamic: needs electricity to hold data. Must be continually replenished with electricity. • FPM: Fast Page Mode • EDO: Extended Data Out • can send data while receiving other data • BEDO: Burst EDO • sends “pipelined” data, speeding up EDO • SDRAM: Synchronous DRAM • runs at the CPU clock speed (faster than prev. types) • today’s main DRAM.

7. Variety of RAM: SRAM • SRAM: Static RAM • static: does not need to be continually refreshed. • more expensive, bigger, and faster than DRAM. • used in CPU chips (caches) • used in “flash memory” image courtesy of Sonystyle.com

8. DRAM: Configurations • Memory modules • SIMMs - 32-bit, require pairing on Pentium systems • DIMMs - 64-bit, do not require pairing on Pentium systems image courtesy of gamespot.com

9. Transistor Capacitor How RAM works • RAM chips have millions of transistor/capacitor pairs. • Capacitors can briefly hold an electric charge. • Gates are opened and closed by the address lines. • Data goes in andout on the data lines image courtesy of How Computers Work CD

10. Data storage: what is it? • Long-term storage, not immediate memory • Not RAM (short-term memory) • Synonyms: secondary storage, auxiliary storage, mass storage images courtesy of dalelabs.com,, iomega.com, imation.com,

11. Data storage: where is it? • Storage involves 2 parts: the device & the media • Removable vs. fixed media • Where can you store data? • magnetic media • optical media • magneto-optical media • solid state media image courtesy of How Computers Work

12. Storage characteristics • Random vs. sequential access • Tracks & sectors • Speed • spin rate (RPM) • seek time & latency • access time • data transfer rate • Storage Capacity • areal density • size Image courtesy of How Computers Work

13. Magnetic data storage • Use magnets to store bits: • example: 0 = N , 1 = S • Reading and writing • Floppy disk drives • Hard disk drives PACE image courtesy of How Computers Work

14. Floppy disk drives: types • Low-density floppy drives: 5.25” floppy disks3.5” 1.44 MB floppy disks • High-density floppy drives: Zip disks, LS-120 disks Images courtesy of How Computers Work, Imation.com, and Iomega.com

15. Floppy disk drives: how they work • Shutter opens with an arm. • Cookie spins on the spindle. • Read/write heads get close to the cookie inside • Magnetic particles generate electric currents in the heads. • Electric currents are interpreted as a series of bits. Images courtesy of How Computers Work

16. Hard disk drives: overview • Glass platters coated with magnetic particles • Read/write heads like floppy drives but much smaller • Multiple platters, multiple heads. Image courtesy of How Computers Work

17. Hard disk drives: how they work • Platters spin on the spindle. • Heads move over the platters. • To read, magnetic particles generate currents in the heads. • Electric currents are interpreted as a series of bits. • To write, the electric currents manipulate the magnetic particles on the platters. Images courtesy of How Computers Work

18. Optical Storage • Instead of using magnetism to store bits, we use light • A laser is the light • Laser: “light amplification by stimulated emission of radiation” • Extremely focused, narrow beam of powerful light • Depending on the wavelength, the beam can be narrower or wider • Lands are flat areas on the disc • Reflect light like a mirror • Pits are holes in the disc • Scatter light Courtesy of http://www.microserve.net/~tpetchy/DVD.shtml

19. CD Drives: Types and Operation • CD-ROM drive speeds: how many times faster than the original CD-ROM drives • 2x, 4x, 6x, 8x, 16x, 32x, 48x • Operation: • Diode generates laser • Laser bounces off mirrors, reaching the disc • Disc reflects or scatters laser • Light-sensing diode sees the reflections, comparing them to a timing circuit to generate 0s and 1s Image courtesy of c-cube.com

20. Types of Optical Discs • Compact discs: • CD-ROM: read only memory (680 MB) • CD-R: Recordable (650 MB) • CD-RW: ReWritable (495 MB) Image courtesy of c-cube.com

21. Types of Optical Discs • Digital versatile discs – higher density storage • DVD-ROM: read only memory (4.7 – 17 GB) • DVD-R: Recordable (3.9 GB?) • DVD-ram (5.2 GB) & DVD+RW (6.0 GB): Rewritable (still fighting) Image courtesy of c-cube.com