🚀 go-pugleaf

 The following information comes from the "IIci Technical Tour" stack,
and hopefully should answer at least some of the questions that have
been posted here recently. The usual disclaimers apply.

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oo Memory Upgrade Issues oo

To satisfy the timing requirements of the 25 MHz 68030, the IIci requires
a RAM speed of 80 ns or faster.  To satisfy the requirements for burst
reads, the IIci requires RAM that supports fast page mode.  Use of RAM
that does not satisfy both requirements will cause the IIci to crash.

The part numbers for Apple labeled SIMM upgrades and service parts that
meet these requirements are listed below:

Finished Goods RAM Upgrade Packages:
Upgrade Size                            Part Number
---------------------------------------------------
1MB, 80 ns, Fast Page Mode              M0291LL/A
4MB, 80 ns, Fast Page Mode              M0292LL/A
4MB (Parity), 80 ns, Fast Page Mode     M0294LL/A

Service Goods RAM SIMM Parts:
RAM Density                             Part Number
---------------------------------------------------
256KB, 80 ns, Fast Page Mode            661-0519
1MB, 80 ns, Fast Page Mode              661-0520
1MB (Parity), 80 ns, Fast Page Mode     661-0546

Unknowing or curious users will undoubtedly try RAM SIMMs that are rated
slower than 80 ns.  In most cases, those users will find that the slower
RAM will work for a short time.  However, the IIci unit WILL eventually
crash with a serious system error.  There are several reasons why a IIci
will not always crash immediately on power up when slower RAM is installed.
They include:

o Frequently, RAM speed is rated conservatively.  As a result, a chip may
  actually be faster than it is rated under certain circumstances.

o Many of the RAM SIMMs that are available on the market for use in the
  Macintosh SE/30, II, IIcx and IIx, including some sold by Apple, are
  rated for 100 ns, which puts them close to the 80 ns requirements.

o RAM speed is higher in a cooler chip than in a warmer chip with the same
  rating.  When the Macintosh is first turned on, the chips are cool.
  After the unit is turned on, the chips will heat up, which causes them
  to slow down.

The rules that must be followed when installing RAM SIMM modules in a IIci
are:

o All SIMM boards within a bank must be the same density.

o Within a bank that contains RAM, all four slots in that bank must be
  filled.

NOTE: Although the following two rules apply to RAM configurations in all
other modular Macintosh models, they ARE NOT required in the IIci.

o All SIMM boards must be installed in Bank A for configurations that fill
  only one bank.

o Higher density SIMM boards must be installed in Bank A for configurations
  that have different densities in each bank.

Bank A and Bank B each hold 4 SIMM strips. The following Apple memory
upgrades work in the IIci:

Bank A and B: Can hold SOJ (small) or DIP (tall) SIMM strips.

Upgrade Options for each bank:
o One M0291LL/A Apple 1MB  Memory Expansion Kit (1MB)
o One M0292LL/A Apple 4MB Memory Expansion Kit (4MB)
or
o One M0294LL/A Macintosh 4MB Parity Memory Expansion Kit (4MB)

1MB IIci (Starting Configuration):

End Cofig.    Upgrade Needed
----------------------------
1MB           *1
2MB           1-M0291LL/A
4MB           1-M0292LL/A *1, *2
5MB           1-M0291LL/A *3
8MB           1-M0292LL/A

4MB IIci (Starting Configuration):

End Cofig.    Upgrade Needed
----------------------------
4MB           *1
5MB           1-M0291LL/A *3
8MB           1-M0292LL/A

4MB Parity IIci (Starting Configuration):

End Cofig.    Upgrade Needed
----------------------------
4MB           *1
5MB           *4, *3
8MB           1-M0294LL/A 

*1 - To achieve this configuration, all four SIMM modules can be installed
     in either Bank A or Bank B.  If built-in video is to be used, all four
     must be installed in Bank A.  If all four are installed in bank B,
     built-in video will be disabled.

*2 - To achieve this configuration, the new SIMM modules will be installed
     in place of the original SIMM modules.

*3 - To maximize performance, install the 1MB SIMM modules in Band B and
     the 256KB SIMM modules in Bank A.  Although the opposite configuration
     can be installed, the effects of cycle stealing for built-in video can
     be minimized by installing the smaller of the two in Bank A.

*4 - Apple is not offering 256KB Parity SIMM modules, so this configuration
     would have to be achieved with third-party 256KB SIMMs.

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