Separate memory modules on a standardized interface provide several advantages:
- Reduced overall production cost
- Greater flexibility in RAM selection
- expansion way beyond what a classic (pre-SIMM) motherboard would support.
- Reduced motherboard design cost
- Greatly reduced motherboard production cost
- Faster innovation cycles due to defined and spacious interface definition
- Move of RAM choice and investment to point of sales (or later)
- More option and reduced investment for retailers.
- Modules will be usable across different brands and boards.
And maybe most important
- Greatly reduced cost of memory cards (in addition to reduced mainboard cost)
The advantage with ZIP over DIP was obvious - more RAM chips in the same board area. Of course, you needed different sockets.
That's why it was added, and especially used in graphics cards, where space was always a premium - at least when trying to provide upper end features - And RAM was (more often than not) already provided in full with the card.
SIMM offered the same space advantage, but with a more complicated socket and with the RAM chips having to be soldered onto a PCB. Overall, seems like a more costly way to go than ZIP RAM, but SIMM obviously won in the market.
Not really, as it reduced the amount of parts. Instead of having a socket for each and every ram chip a single socket was needed holding 8 (or sometimes up to 32) chips. Quite a reduction from the point of a motherboard manufacturer. The memory modules itself could carry the chips without any socket. Further it allowed to separate RAM mounting technology (thruhole or SMD) from motherboard manufacturing. A SIMM Module could use any kind of RAM, no matter if it is DIP, SIP, ZIP or SMD like TQFP or BGA.
It further decoupled RAM pinout from motherboard layout. Now larger or smaller RAMs from various manufacturers could be incorporated. This include pinouts that were not known/available at the point the motherboard was designed.
And most important, it removed the need to design a motherboard for a specific amount of memory and, as follow up, the design of specific memory cards. A motherboard can only hold sockets for a specific amount of RAM of a specific pinout. When they are filled, some kind of memory or I/O bus card must be made to add more memory.
Using memory modules is, well, modularization. Much like having a nice, clear API, designed with an upgrade path in mind allows independent development and sales.
So why were the added manufacturing costs for SIMMs not an issue and why did they quickly replace ZIPs?
Because manufacturing costs were not higher but lower. Lower for all parties involved, Motherboard and RAM module manufacturers as well as retailers.
- On the motherboard side, buying one (complex) socket is less expensive then adding 32 (or more) single chip sockets.
- Similar, placing one (or even 4) SIMM sockets is faster and less expensive than 32 separate sockets.
- For the RAM manufacturer the board design will be way less expensive than for a traditional (large) memory expansion board (like ISA Memory cards for the PC).
- Similar board production will cost way less.
- For the retailer taking the RAM (socket/space) cost out of the motherboard reduces upfront investment on motherboards, as well as on RAM modules
Note: I get that SIMM insertion and removal is relatively easy, but that ease-of-upgrade option only makes sense if it was a major consumer selling point. My recollection is that most motherboard RAM upgrades happened at the point-of-sale, with vendors likely choosing the cheapest solution.
The profit of vendors/resellers configuring a PC is quite dependent on the time invested to configure a PC to the customers specs, and inserting 8, 16 or more flimsy ZIP chips without bending a pin and good insertion and so on, is a great burden compared with clipping in one or two SIMMs. Time is money.
Stock cost is as well important for a vendor/reseller. Modularized structure does enable a considerable lower stock by only holding a few different memory modules instead of many different chips and even more model specific memory expansion boards.