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Understanding Various Memory Types: From ROM to Flash and RAM

This lecture explores different types of memory, highlighting Read Only Memory (ROM), Programmable ROM (PROM), Erasable PROM (EPROM), Electrically Erasable PROM (EEPROM), FLASH, and Random Access Memory (RAM). It details the unique characteristics of each memory type, such as how they operate, their structures, and application contexts. Key distinctions include the permanence of data storage, erasure methods, and the specific circuitry involved. This comprehensive overview serves as a foundation for understanding memory technology in computing.

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Understanding Various Memory Types: From ROM to Flash and RAM

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  1. ECT 358 Lecture 18 Memory

  2. Blessed is he who, having nothing to say, refrains from giving wordy evidence of the fact. The tongue of the wise useth knowledge aright: but the mouth of fools poureth out foolishness. Proverbs 15:2

  3. Memory Types • Read Only Memory (ROM) • Programmable Read Only Memory (PROM) • Erasable PROM (EPROM) • Electrically Erasable PROM (EEPROM) • FLASH • Random Access Memory (RAM) • Static RAM (SRAM) • Ferroelectric Nonvolatile Memory

  4. Read Only Memory (ROM) • Memory remains unchanged during operation and after power is removed • Structurally modified for program • Address and Data lines • Address Decoder • Bipolar/CMOS/nMOS/pMOS

  5. Read Only Memory (ROM)

  6. Programmable ROM (PROM) • Similar structure to ROM • One time programmable • PROM burner • Bipolar technology • Can be modified slightly (unburnt fuses)

  7. Programmable ROM (PROM)

  8. Erasable PROM (EPROM) • Similar to PROM • Floating nMOS transistor gate • Additional gate • High programming voltage • UV erasable • Bulk erase • 20 minute erase time

  9. Erasable PROM (EPROM)

  10. Electrically Erasable PROM (EEPROM) • Similar to EPROM • Electrically erased vice UV erased • Electrical pulses break down gate • High negative charge (-15 volts) • Programmed in circuit with low voltage • Individual words erased • 100-100000 erase cycles • Much faster than UV for erasing

  11. Electrically Erasable PROM (EEPROM)

  12. FLASH • Similar to EEPROM’s • Additional circuitry to selectively erase and program the device in circuit • Lower power consumption • Simultaneous erasing of blocks • Multiple bits per cell (1-3 levels) • 100000 erase cycles

  13. FLASH

  14. Random Access Memory (RAM) • Contents changed during operation • Data lost when power is removed • RAM circuit is fixed, not programmed • RAM contents are programmed • Requires refresh

  15. Static RAM (SRAM) • Transistor-Capacitor storage cell structure that does not require refresh • Fast Cache • 6 transistor circuit • Wide input decoder • Rectangular versus square physical layout

  16. Ferroelectric Nonvolatile Memory • Hysteresis effect • Electrical polarization under applied voltage • Hard Drives • Magnetic Tape • Floppy Drives • Drum Drives • Bi-stable states

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