1. RAM (random access memory)
RAM is a semiconductor that stores charges with transistors and capacitors.
DRAM- Dynamic RAM
Most popular type of electronic memory in the PC world.
Must be refreshed constantly or it loses its contents
SRAM- Static RAM- very expensive
does not have to be refreshed

2. RAM Random Access Memory
Originally RAM had a 640 K limit
The 8088 could use only use 256 K per row
Needed improved MCC before more RAM could be added

3. MCC and Parity MCC- Memory Controller Chip Parity
“Fetches” memory for the CPU from RAM
Parity
Extra chip
For error detection
Usually seen as a “ninth” or odd number chip
MCC must be designed to handle parity

4. Evolution of RAM packages
DIPPS- first generation of DRAM chips
2 rows on either side
easy to install wrong or break
Installed a chip at a time
Needed to create a row
So why have to install all chips?

5. 30 pin SIPPS
Page 160- With SIPPS RAM was on a small board that installed on motherboard
Memory was more than one bit wide, so you could have more memory and fewer rows
But pins were still easy to break

6. 30 Pin SIMMS No visible pins hanging off, so you couldn’t break it
Always 8 bits wide, though depths could vary
Can’t tell depth by looking at it
Whether you need parity depends on motherboard
You can disable parity in CMOS

7. Access in Nanoseconds (ns)
The lower the better. 200 ns on the 8088, now less than 50 ns

8. Banking Accessing more than one row of DRAM at a time
Only possible with the 286 and later
Width of RAM must equal external data bus
RAM was always 8 bits wide
More rows were added to equal data bus
8 bits times 4 rows equals 32 bits

9. Banking continued All SIMMs in the same bank must be identical
You can have different total types but all of the members of one bank must be identical
All SIMMs in bank should be same speed
Totally “populated” or totally “unpopulated”

10. On to the 72 pin SIMMs
Modern Computers needed too many 30 pin SIMMs to make a bank to match the modern 64 bit data bus
New memory needed, to eliminate space
The 72 pin SIMM is 32 bits wide, not 8 bits like previous RAM like 30 pin SIMMs
Only 2 SIMMs needed for bank in Pentium

11. 168 Pin DIMM
DIMM: Dual-inline memory module (has DRAM chips on both sides)
64 bits wide, not 32
Each side of each pin has separate function
SO-DIMMS used in laptops and have only 72 pins so are much shorter
A bank is formed when
X * Width of SIMM chip=Width of external data bus X=sticks in one bank
Can you mix DIMMs and SIMMs?

12. Types of RAM
EDO- Extended data out- doesn’t need to be refreshed as often. Can be on either 72 pin SIMM or 168 pin DIMM. Don’t mix with FPM RAM
SDRAM- Synchronized DRAM tied to system clock, 5 times faster than DRAM. Is available only on DIMMs
ECC RAM- Errors detected and fixed

13. ROM- Read-only memory
PROM- Programmable Read Only Memory- can be programmed only once and are then read only- cannot be erased or changed
EPROM- Erasable Programmable Read Only Memory
EEPROM- Electrically Erasable Read-Only Memory