RAM types and features

RAM types and features

1. RAM Types

   • Static RAM (SDRAM)/Cache
     • Faster than dynamic
     • high speed - directly accessible by the CPU
     • Expensive
   • Dynamic RAM
     • SIMMS and DIMMS
     • data lost during transfer and processing by CPU
     • DDR - 184-pin
     • DDR3- 240-pin
     • DDR2 - 240-pin

2. Single-sided vs double-sided

   • Single Sided
     • Expansion bank of RAM
     • all available memory accessible by computer
   • Double-sided
     • 2 banks of memory but only accessed one at a time

3. Parity vs Non-Parity

   • Older checking method
   • 8 bits data - 9th being parity
   • piece of data equal to another
   • ERROR - parity bit values of 2 strings of data do not match
   • display error or stop system
   • servers

4. Buffered & non-buffered

   • Buffered
     • chips to assist memory controller - large amounts of memory installed
     • Servers
     • contains ECC
     • extra chips means latency
     • no gaming
   • Non-buffered
     • communicated directly with memory controller
     • Workstations and gaming

5. ECC vs Non-ECC

   • ECC
     • Error Correcting Code
     • uses several bits in a data string for error checking
     • DIMM with ECC - extra chip
       • uses extra 8 bits for checking
     • upper end systems
   • Non-ECC
     • Desktops
     • Employs parity - errors detected within data

6. RAM Configurations

   • how fast data transferred between chips on board
   • Single Channel
     • slowest/ access one DIMM at a time
   • Dual Channel
     • 2 DIMMS at a time
   • Quad Channel
   • Triple Channel

7. RAM Compatibility

   • memory modules of different speeds cause faster modules to run at the speed of the slowest module
   • CAS Latency (Column Address Strobe)
     • signal processor - memory circuit, activate column address
     • Latency - how many clock cycles to read/write a column of data
   • Timing
     • Row Access Strobe (RAS)
       • no. cycles that must pass before the system can access one of the row's columns
     • Row Pre-Charge Time (RP)
       • how many cycles must pass before another row can be selected
     • Row Active Time
       • min no. cycles a row needs to be active to make sure there is enough time to access the info stored in the row