Mac II 

Special “PAL” SIMMs required when using 4, 8, or 16MB 
SIMMs. Special motherboard socket for PMMU.

Physical Memory: Uses 256K and 1MB SIMMs. Memory 
configurations from 1 to 8 megabytes are achieved following 
the usual rule for Modular Macs: each bank of 4 sockets must 
be either completely filled with 4 SIMMs of the same size, or 
left completely empty. Bank A must always be filled.  In 32-bit 
addressing, up to 68MB can be installed, but it is a little 
complicated.  Special “PAL” SIMMs required when using 4, 
8, or 16MB SIMMs. Three distinct issues all limit Mac II 
memory configurations over 8MB:

1)The Mac II ROMs are not compatible with 32–bit 
addressing. Extra software must be added in order to access 
more than 8 megabytes. Under System 7, the best solution is usually MODE32, which overcomes this limitation by enabling standard 32–bit addressing (see “Using Large Amounts of Memory”). 32–bit addressing is also available under System 6 by using OPTIMA (although OPTIMA is not compatible with MultiFinder). In either System 6 or 7, MAXIMA can be used to enhance the 24–bit addressing mode, allowing up to 14MB to be addressed. RAM Doubler, MODE32, MAXIMA, and OPTIMA all require a PMMU on the Mac II.

2)Special SIMMs are required on the Mac II. The special design incorporates the usual eight 4–megabit DRAM chips as well as a PAL or equivalent logic chip. A logic chip is needed to overcome problems caused by the refresh logic on the Mac II (and IIx). These two systems were designed before 4MB SIMMs became available and turned out not to be compatible with the final standard design of 4MB SIMMs. (Do not confuse these special SIMMs with the somewhat similar 9–chip “parity” SIMMs used for government and other applications, where the 9th chip is also DRAM. Parity SIMMs will not overcome the memory problem.) Many vendors now offer compatible SIMMs for the Mac II and IIx, though they do cost a little more than standard SIMMs. Be sure to specify what Mac you use when you buy 4, 8, or 16 MB SIMMs. These special SIMMs are also compatible with the Classic II, IIcx, IIci, IIsi, SE/30 and Quadras (but not the IIfx), although they are not required on these systems. (The same problem applies to the unusual 1MB SIMMs built from 2 4–megabit DRAM chips, so you should use the much more common 8 1–megabit chip 1MB SIMMs on the Mac II and IIx.)

3)On a standard Mac II, Bank A cannot use SIMMs larger than 1MB. Four, 8, and 16MB SIMMs must only be put in Bank B. Also, Bank A must be filled with SIMMs of 1MB or less if Bank B is to be used. Bank A is the set of four sockets to the right as you face the front of the Macintosh. This is a problem unique to the Mac II, and is caused by problems in the Mac II ROMs which is not overcome by adding MODE32 or MAXIMA. However, you can fix this one problem by installing the HDFD SuperDrive upgrade kit, which includes a set of Mac IIx ROMs. As a result of this limitation the largest memory configuration available on unmodified Mac IIs using 1MB and 4MB SIMMs is 20MB: four 1MB SIMMs in Bank A and four 4MB SIMMs in Bank B. When Mac IIx ROMs are added, the maximum amount of memory the computer will support is 128MB, using eight 16MB SIMMs. To get 68MB, put four 1MB SIMMs in Bank A and four 16MB SIMMs in Bank B.

Extended Memory: The Mac II is equipped with a Motorola 68020 CPU (not the 68030 of the more recent systems). Because of this it needs a memory coprocessor to run virtual memory–the Motorola MC68851RC16A Paged Memory Management Unit (PMMU). The PMMU allows use of RAM Doubler, System 7 VM, A/UX, MODE32, Virtual, and MAXIMA on the Mac II. It does not otherwise affect performance and should not be confused with the Motorola 68882 math coprocessor, designed to accelerate mathematical computation. In 24–bit mode the Mac II can address up to 13MB of VM, and in 32–bit mode (MODE32 required), it can address up to 1024MB. Where performance is critical, or hard drive space is limited, we recommend RAM Doubler.

Mac IIx 

Eight SIMM sockets in two banks of four each. 120ns SIMMs 
or faster. Virtual memory, 32–bit addressing with MODE32. 
Can be upgraded to IIfx (see “Mac IIfx”).

Physical Memory: Uses (standard) 256K and 1MB SIMMs.  
24-bit addressing memory configurations from 1 to 8 
megabytes are achieved following the usual rule for Modular 
Macs: each bank of 4 sockets must be either completely 
filled with 4 SIMMs of the same size, or left completely empty.
Bank A must always be filled.  In32-bit mode, up to 128MB of 
physical RAM may be installed on a Mac IIx (eight 16MB 
SIMMs). Special “PAL” SIMMs are required for 4MB SIMMs 
or larger. A common large memory configuration is eight 4MB 
SIMMs for a total of 32MB. In System 7 MODE32 and/or 
MAXIMA software must be added to address more than 8MB 
of RAM. Under System 6 use MAXIMA or OPTIMA.  See the description of the Mac II for a discussion of memory issues on the Mac IIx.

Extended Memory: The 68030 CPU in the Mac IIx has a built–in Memory Management Unit. Therefore, the Mac IIx can run RAM Doubler or virtual memory without requiring any additional hardware. In 24–bit mode, the Mac IIx can address up to 13MB of VM, and in 32–bit mode (MODE32 required), it can address up to 1024MB. In situations where performance is critical, or hard drive space is limited, we recommend RAM Doubler.

Mac IIcx 

Physical Memory: Uses 256K and 1MB SIMMs.  24-bit 
addressing memory configurations from 1 to 8 megabytes 
are achieved following the usual rule for modular Macs: each 
bank of 4 sockets must be either completely filled with 4 
SIMMs of the same size, or left completely empty. Bank A 
must always be filled.  In32-bit mode, up to 128MB of 
physical RAM may be installed on a Mac IIcx (eight 16MB 
SIMMs). A common high memory configuration is eight 4MB 
SIMMs for a total of 32MB. The Mac IIcx ROMs are not 
compatible with 32–bit addressing. Extra software must 
always be added in order to access more than 8 megabytes. 
Under System 7, the best solution is MODE32, which 
overcomes this limitation by enabling standard 32–bit 
addressing (see “Using Large Amounts of Memory”). 32–bit 
addressing is available under System 6 Finder by using
OPTIMA.). In either System 6 or 7, MAXIMA can enhance the 24–bit addressing mode, allowing up to 14MB to be addressed.

Extended Memory: The 68030 CPU in the Mac IIcx has a built–in Memory Management Unit. Therefore, the Mac IIcx can run RAM Doubler or virtual memory without requiring any additional hardware. In 24–bit mode, the IIcx can address up to 13MB of VM, and in 32–bit mode (MODE32 required), it can address up to 1024MB. In situations where performance is critical, or hard drive space is limited, we recommend RAM Doubler.

Mac SE/30 

Physical Memory: Uses 256K and 1MB SIMMs.  24-bit mode
 memory configurations from 1 to 8 megabytes are achieved 
following the usual rule for Modular Macs: each bank of 4 
sockets must be either completely filled with 4 SIMMs of the 
same size, or left completely empty. Bank A must always be 
filled.  In 32-bit mode, up to 128MB of physical RAM may be 
installed on an SE/30 (eight 16MB SIMMs). A common high 
memory configuration is eight 4MB SIMMs for a total of 
32MB.  In System 7 MODE32 and/or MAXIMA software must 
be added to address more than 8MB, but standard SIMMs
may be used. Under System 6, use MAXIMA or OPTIMA.

The SE/30 looks like a Compact Mac, but actually has 
memory architecture like the Modular Macs. With no 
additional software, up to 8MB of memory can be addressed 
in 24–bit mode on the SE/30, while only 4MB can be addressed using the Compact Macs. So, for example, if you put a total of 8MB of RAM (eight 1MB SIMMs) in an SE/30 running System 7 (with 32–bit addressing On or Off), you would get 8MB of application memory. (See “Using Large Amounts of Memory,” and “More Than 4MB on Compact Macs”)

Extended Memory: The 68030 CPU in the SE/30 has a built–in Memory Management Unit. Therefore, the SE/30 can run RAM Doubler or virtual memory without requiring any additional hardware. In 24–bit mode, the SE/30 can address up to 13MB of VM, and in 32–bit mode (MODE32 required), it can address up to 1024MB. 

Many SE/30 systems have 40MB hard drives. For these systems we recommend RAM Doubler.

Mac IIsi 

Physical Memory: The bank may either be empty, or filled 
with four SIMMs, which must all be of the same size. 24-bit 
mode memory configurations of 1, 2, 3, or 5MB are therefore 
possible using no SIMMs, 256K, 512K or 1MB SIMMs in the 
bank, respectively. The IIsi and IIci are the only Macs that 
support 512K SIMMs.  In 32-bit mode, up to 65MB of physical 
RAM may be installed on a Mac IIsi (1MB soldered on the 
motherboard plus four 16MB SIMMs). A common 
configuration is 17MB (1MB built–in plus four 4MB SIMMs). 
The Mac IIsi has 32–bit compatible ROMs, so no additional 
software is required to be in 32-bit mode in System 7. Under 
System 6, use MAXIMA or OPTIMA. 

Extended Memory: The 68030 CPU in the Mac IIsi has a built–
in Memory Management Unit. Therefore, the Mac IIsi can run 
RAM Doubler or virtual memory without requiring any additional hardware. In situations where performance is critical, or hard drive space is limited, we recommend RAM Doubler.

On the IIsi, System 7 VM will only provide 12MB instead of the usual 13MB in 24–bit addressing mode. Connectix Virtual provides 14MB in 24–bit mode, as usual. In 32–bit mode either virtual memory manager can support up to 1024MB.

Mac IIvx 

Physical Memory: The bank may either be empty, or filled 
with four SIMMs which must all be of the same size. 24-bit 
mode memory configurations of 4, 5, or 8MB are possible 
using no SIMMs, 256K, or 1MB SIMMs in the bank.  In 32-bit 
mode, up to 68MB of physical RAM may be installed on a 
Mac IIvx and Performa 600(4MB soldered on to the
motherboard plus four 16MB SIMMs). Other common 
configurations are 16MB (4MB built in plus four 2MB SIMMs) 
or 20MB (4MB built in plus four 4MB SIMMs). They have 
32–bit compatible ROMs, so no additional software is
 required to be in 32-bit mode in System 7.

Extended Memory: The 68030 CPU in the Mac IIvx has a 
built–in Memory Management Unit.  Therefore, they can run 
RAM Doubler or virtual memory without requiring any 
additional hardware. In 24–bit mode, the IIvx can address up to 13MB of VM, and in 32–bit mode, it can address up to 1024MB. In situations where performance is critical, or hard drive space is limited, we recommend RAM Doubler. 

Video RAM: The IIvx has two VRAM banks of one slot each. In the standard configuration, one of the banks has 512K of 68–pin VRAM installed in it. This is enough to support 16–bit color on the 12" RGB monitor, or 8–bit color on the 13" or 14" color monitor. This can be expanded up to 1MB by putting another 512K VRAM SIMM in the second bank. This configuration will support 16–bit color on the 13” or 14” color monitor.

Mac IIci 

Physical Memory: Uses 256K, 512K or 1 MB SIMMs.  24-bit 
mode memory configurations from 1 to 8MB are achieved 
following the usual rule for Modular Macs: each bank of 4 
sockets must be either completely filled with 4 SIMMs of the 
same size, or left completely empty. Bank A must always be 
filled. The IIci and IIsi are the only Macs that support 512K 
SIMMs.  In 32-bit mode, up to 128MB of physical RAM may 
be installed on a Mac IIci(eight 16MB SIMMs). The Mac IIci 
was the first Mac to contain 32–bit compatible ROMs, so no 
additional software is required to be in 32-bit mode in System 
7. Under System 6, use MAXIMA or OPTIMA. 

Extended Memory: The 68030 CPU in the Mac IIci has a 
built–in Memory Management Unit. Therefore, they can run 
RAM Doubler or virtual memory without requiring any 
additional hardware. In 24–bit mode, the IIci can address up to 13MB of VM, and in 32–bit mode, it can address up to 1024MB. In situations where performance is critical, or hard drive space is limited, we recommend RAM Doubler.

A unique limitation occurs on the Mac IIci. Bank A addresses are shared between the on–board video and SIMMs, so using 2, 4, 8, or 16MB SIMMs in Bank A can slow the Mac down a lot. Moreover, intermittent crashes can occur if 2, 4, 8, or 16MB SIMMs are put in Bank A, when on–board video is used. If you use on–board video, put the larger SIMMs in Bank B, and be sure to put some smaller SIMMs (1MB or less) in Bank A. If you do not use on–board video, follow the usual rule: put your largest RAM in Bank A.

Parity RAM: Some IIci Macs are equipped with an optional PGC chip that supports a memory error detection system called parity checking. These are usually for government applications. They require special parity SIMMs with 9 RAM chips instead of the usual 8.

Mac IIfx 

Standard Memory: Uses only 1MB SIMMs. 256K and 512K 
SIMMs will not work. The Mac IIfx requires faster RAM than
the earlier Modular Mac systems. The SIMM sockets have 
64 connectors instead of the usual 30, so standard SIMMs 
will not fit in a IIfx.  24-bit mode memory configurations up to 
8 megabytes are achieved following the usual rule for 
Modular Macs: each bank of 4 sockets must be either 
completely filled with 4 SIMMs of the same size, or left 
completely empty. Bank A must always be filled.  In 32-bit 
mode, up to 128MB of physical RAM may be installed on a 
Mac IIfx (eight 16MB SIMMs). A common large memory 
configuration is eight 4MB SIMMs for a total of 32MB. The 
Mac IIfx has 32–bit compatible ROMs, so no additional 
software is required to be in 32-bit mode in System 7. Under 
System 6, use MAXIMA or OPTIMA.

Extended Memory: The 68030 CPU in the Mac IIfx has a built–in Memory Management Unit. Therefore, the Mac IIfx can run RAM Doubler or virtual memory without requiring any additional hardware. In 24–bit mode, the IIfx can address up to 13MB of VM, and in 32–bit mode, it can address up to 1024MB. In situations where performance is critical, or hard drive space is limited, we recommend RAM Doubler.

Parity RAM: Some IIfx Macs are equipped with an optional PGC chip that supports a memory error detection system called parity checking. These are usually for government applications. They require special 60ns parity SIMMs which have 9 RAM chips on them instead of the usual 8.