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Physical Packaging


DIPP - Dual In-line Pin Package
This is the type of component you think of when someone says "chip". You used to have to install individual chips to populate a motherboard's RAM banks. There are DIPPs on SIMMs, SIPPs, and DIMMs.

SIMM - Single In-line Memory Module
Sometimes referred to as stick RAM. It looks like a miniature peripheral card (meaning it has little finger contacts at the bottom), a little bigger than a stick of gum. They come in two main varieties, 30 pin and 72 pin. When physically looking at the stick, 30 pin has..
You guesses it, 30 finger contacts. 72 pin has 72, but an easier way to identify them (without counting the contacts,) is if the contacts are contiguous across the bottom, it's 30 pin. If there is a break in the contacts right in the middle, then it's 72 pin. 168 pin DIMMs also have a break in the finger contacts, but it looks quite a bit different than a 30 or 72 pin SIMM.

SIMMs have a 32 bit data path (meaning it can provide the CPU with 32 bits of data at a time.) 486 motherboards had a 32 bit path, so that is why you could add memory one stick at a time. Pentiums have a 64 bit data path, therefore you have to build evenly (two sticks at a time). A stick of RAM at 32 bits X 2 gives you 64 bits for your data path. There's a type called double sided SIMMs, which are basically two single sticks stuck back to back, but you can only address one side at a time because they use the same control line. Now the double sidedness depends on how the chip is wired. Some single sided SIMMs have chips on both sides of the stick, but aren't actually double sided SIMMs.

Looking at a SIMM, many times it's difficult to tell what type it is, so if you remember these general rules, you should be all right:

  • 1, 4 and 16MB 72 pin SIMMs are single sided.
  • 2, 8 and 32MB 72 pin SIMMs are double sided.

To determine whether the SIMM is parity or not, these general rules will help. BTW, parity is usually referred to as x36 and non-parity as x32:

  • On 30 pin SIMMs, count the number of chips (DIPPs) on the stick. If it's 2 or 8, it's probably non-parity. 3 or 9, it's parity.
  • On 72 pin SIMMs, it's a little more difficult. Generally, if there are 4, 8, 16 or 32 chips, it's non-parity.


SIPP - Single In-line Pin Package
These were a short lived configuration of RAM sticks. The were pretty much physically identical to the SIMMs except that they had pins instead of the finger contacts.

DIMM - Dual In-line Memory Module
These are the relatively new type of RAM modules. They provide a 64 bit data path (upgrade one stick at a time for 64 bit bus systems), and they have 168 pins (finger contacts).

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