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Physical Memory:

 

Static RAM (SRAM): doesn’t need a constant refresh/update; stores info as patterns of transistor ons/offs to represent binary digits; usually stores 256k per IC (Integrated Circuits); used for memory cache.

  • Pairs of transistors
  • Patterns of transistors
  • Constant refresh not required

 
  • 10-20 nS
  • 30-50 degrees C

 

 

Dynamic RAM (DRAM):  stores info. as charges in very small capacitors; a charge present in a capacitor is interpreted as a 1, while the absence as a 0; needs a constant refresh signal to keep the info in memory; requires more power than SRAM; allows several memory units (cells) to be packed with high density; 60 nS; can only access one block of data at a time

  • Fast Page Mode (FPM) DRAM
  • Extended Data Out (EDO) DRAM

 
  • Direct Rambus (RIMM)
  • Double Data Rate SDRAM (DDR SDRAM)
  • Synchronous DRAM (SDRAM)

 

 

Fast Page Mode (FPM) DRAM: released with 486/Pentium transition; allowed data to be “paged” (swapped) for faster access to data in the same row or page; Page-mode memory works by eliminating the need for a row address if data is located in the row previously accessed. It is sometimes called page mode memor; (increased speed of memory access process)

 

Extended Data Out (EDO) DRAM: 1995; ^ performance by 10-15% over FPM DRAM, eliminating memory wait states; can start fetching next block of memory at same time it sends previous block to CPU; allows memory controller to begin a new column address

 

Burst (BEDO) EDO DRAM: can process four memory addresses in one burst; can only stay synchronized with the CPU clock for short periods (bursts); can't keep up with processors whose buses run faster than 66 MHz.

 

Synchronous DRAM (SDRAM): 4th ¼ 1996; synchronized to speed of the system clock (e.g. PC100 runs @ 100 MHz, etc.)

  • Double Data Rate (DDR) SDRAM: clock-doubled SDRAM; memory chip can perform reads and writes on both sides of any clock cycle, doubling the effective memory executions per second (DDR SDRAM @ 100MHz memory bus, the memory will execute reads and writes @ 200 MHz and transfers data to the processor @ 100MHz)

 

Rambus (RDRAM): developed by Rambus, Inc; transfers data at up to 800 MHz; Nintendo 64; allows data transfer through a simple bus OS @ high speeds; 1997, Intel would license Rambus technology for use on its future motherboards, thus making it the likely de facto standard

Direct Rambus (RIMM):  Memory Modules for RDRAM; data rate @ 800 MHz over 16bit memory bus; transfer data on both the rising and falling edges of a clock cycle; high bandwidth of up to 1.6GB/s (more than 2x 100MHz SDRAM)

Synchronous Link (SLDRAM): 1999 now defunct SyncLink Consortium

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ROM:  memory chip - contains transistors manufactured permanently in the on or off position. (switches)  (BIOS is a ROM chip)

Programmable ROM (PROM): 1st manufactured w/ all of its circuits as logical 1s (on switch); then when the PROM was programmed, the connections that need to be set to 0 are destroyed, using a high voltage electrical pulse to make the settings permanent; PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, use a PROM programmer (PROM burner) – or burning the PROM

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Erasable Programmable Read Only Memory (EPROM): erasable and able to be reprogrammed; store binary info as electrical charges deposited on the chip (almost permanent); deposits destroyed by special-frequency ultraviolet light shone through a small window; exposure turns the chip to its blank state; then the chip can be reprogrammed; identified by small circular windows. (IBM PC or XT, may use EPROMs for BIOSs)

 

Electrically Erasable PROM (EEPROM): erased by exposing it to an electrical charge (special sequence of electric signals); primarily used for BIOS info; requires data to be written or erased one byte at a time

CMOS (complementary metal oxide semiconductor) memory: keeps BIOS settings while computer off; holds date, time, and system setup parameters; CMOS battery lasts for several years; (replace if computer loses BIOS settings when powered off)

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Video RAM (VRAM): can be accessed by 2 different devices simultaneously (enables RAMDAC to access VRAM for screen updates at the same time that the video processor provides new data to the CPU.

Windows Accelerator Card RAM (WRAM): developed by Samsung Electronics that supports two ports - enables the adapter to fetch the contents of memory for display at the same time that new bytes are being pumped into memory; similar to VRAM, but more cost effective because it supports addressing of large blocks (windows) of video memory.

 

Memory Bank
Memory chips (8/16/32bits)

SIMMs: hold up to eight (Mac) or nine (PC) RAM chips; 32bit bus; because the Pentium processor requires a 64-bit path to memory, you need to install SIMMs two at a time; used w/ AT, MCA, EISA systems; 72pins/32bits

DIMMs: 168pin/64bit path; opposing pins remain isolated to form 2 separate contacts

Parity chips vs. non-parity chips

Physical Memory                Logical Memory  Memory Optimization        Memory Troubleshooting