CompuServe Thread

PI >>But if a 4×32/36 is a 16meg SIMM, what's a 4×1 or a 4×9?<< From my understanding… With RAM, each chip supplies a slice (a bit) of the whole, instead of a complete RAM area. If you were to go out to your car and pull one of the wheels off, then take a saw, and slice up the wheel like a pizza… you would see how RAM chips work. Each slice is part of the whole wheel. If the wheel is sliced into 8 pieces, then you need all eight piece to be in place to get the wheel to roll. If the wheel were sliced into 2 pieces, you would need the two piece to form the whole wheel. RAM chips work the same way. However, instead if slicing one chip into 8 pieces that fit to gether, they already come as 8 pieces to be linked together. — A 256×1 chip, has 256-Kbits (yes kilobits) with a wide of 1 bit. To form a full 256K (kilobyte), requires eight of these chips. The A500 rev5, used *16* 256×1 chips to give it 512K of CHIP memory. A 256×4 bit chip, has 256-Kbits, but with a width of 4 bits. To form a full 256K, requires only two of these chips. The A500 rev6, used only *4* 256×4 chips to give 512K of CHIP memory. The 1×1 chips, have 1-megabit (1024 kilobits) with a width of 1 bit. While the 1×4 chips are 1-megabit with a width of 4 bits. You needed either eight 1-bit chips to form 1024K, or two 4-bit chips to form 1024K. So: 1megabit x 1bit times 8 chips = 1megabyte of RAM 1megabit x 4bit times 2 chips = 1megabyte of RAM — A SIMM, places the chips into a plug & go package, instead of having the users plug the chips (one at a time) into a memory board. The chips are already grouped, so each SIMM functionally provides the full 8-bits. A 256K SIMM would be labeled 256×8. You would need only one SIMM to make 256K of memory. A 1-meg SIMM would be labeled 1×8 (1megabit x 8). There will be some SIMMs labeled 256×9, 512×9, 1mx9, etc., these SIMMs has an extra chip that is used by some computers (IBM/Clones) to do parity checking on the memory. The extra bit (chip), is invisible to most other computer systems. It is possible to find SIMMs with 8 (1bit), 9 (1bit+parity), 2 (4bit), or 3 (4bit+parity) chips mounted on the SIMM. Some SIMMs will use both sides to mount chips, while others use only one side, and a third design that mount the regular chips on one side with parity chips on the other side. — A 4mx8 (4megabit x 8bits) SIMM would be a SIMM that could provide all eight bits for 4-megabytes. This would probably use eight 1Mx4 chips, mounted on one side of the SIMM. — At this point we've been talking about 8-bit (9-bit) SIMMs, were a SIMM reguardless of memory size provides only 8-bits. If a system wanted 32-bit memory, you used four 8-bit SIMM modules to create 32-bits. I saw a CPU+RAM board for the A2000. It had 16 SIMM sockets for adding 1mx8, or 4mx8 SIMMs. But it required memory to be added 4 SIMMs at a time. The new 72-pin SIMMs used by the A1200/4000 are 32-bit SIMMs. A single 256Kx32bit SIMM could replace four 1Mx8bit SIMMs. A 1Mx32bit SIMM can replace four 4mx8bit SIMMs. 32bits = 8bits = megaBYTES 256×32 = 1024×8 = 1M 1024×32 = 4096×8 = 4M A 4×32 SIMM, would be a 4-megabits (4096) times 32-bits. 4096×32 = 16384×8 = 16M — Does this answer your question? Ron. – ap'ing with AP. (Eagles may fly, but weasels aren't sucked into jet engines.)