Presentation on theme: "RAM (random access memory)"— Presentation transcript:
1 RAM (random access memory) RAM is a semiconductor that stores charges with transistors and capacitors.DRAM- Dynamic RAMMost popular type of electronic memory in the PC world.Must be refreshed constantly or it loses its contentsSRAM- Static RAM- very expensivedoes not have to be refreshed
2 RAM Random Access Memory Originally RAM had a 640 K limitThe 8088 could use only use 256 K per rowNeeded improved MCC before more RAM could be added
3 MCC and Parity MCC- Memory Controller Chip Parity “Fetches” memory for the CPU from RAMParityExtra chipFor error detectionUsually seen as a “ninth” or odd number chipMCC must be designed to handle parity
4 Evolution of RAM packages DIPPS- first generation of DRAM chips2 rows on either sideeasy to install wrong or breakInstalled a chip at a timeNeeded to create a rowSo why have to install all chips?
5 30 pin SIPPSPage 160- With SIPPS RAM was on a small board that installed on motherboardMemory was more than one bit wide, so you could have more memory and fewer rowsBut 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 varyCan’t tell depth by looking at itWhether you need parity depends on motherboardYou 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 laterWidth of RAM must equal external data busRAM was always 8 bits wideMore rows were added to equal data bus8 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 identicalAll SIMMs in bank should be same speedTotally “populated” or totally “unpopulated”
10 On to the 72 pin SIMMsModern Computers needed too many 30 pin SIMMs to make a bank to match the modern 64 bit data busNew memory needed, to eliminate spaceThe 72 pin SIMM is 32 bits wide, not 8 bits like previous RAM like 30 pin SIMMsOnly 2 SIMMs needed for bank in Pentium
11 168 Pin DIMMDIMM: Dual-inline memory module (has DRAM chips on both sides)64 bits wide, not 32Each side of each pin has separate functionSO-DIMMS used in laptops and have only 72 pins so are much shorterA bank is formed whenX * Width of SIMM chip=Width of external data bus X=sticks in one bankCan you mix DIMMs and SIMMs?
12 Types of RAMEDO- 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 RAMSDRAM- Synchronized DRAM tied to system clock, 5 times faster than DRAM. Is available only on DIMMsECC RAM- Errors detected and fixed
13 ROM- Read-only memoryPROM- Programmable Read Only Memory- can be programmed only once and are then read only- cannot be erased or changedEPROM- Erasable Programmable Read Only MemoryEEPROM- Electrically Erasable Read-Only Memory