SIMMs (single in-line memory modules) were an innovation created in 1982 to allow memory to be installed on a separate circuit board and connected to the main board through a dedicated pin connector. SIMMs (and the related SIPP modules) allowed larger quantities of DRAM to be installed without occupying valuable space on the main board.
Over its timespan, 30-pin SIMMs were produced in 256K, 1MB, 2MB, 4MB, and 16MB capacities. The pin arrangement limited the maximum number of addressable RAM to 16MB. This limitation led to the development of the 72-pin SIMMs, which were commonly used throughout the 1990s.
Apple began incorporating 30-pin SIMMs with the Macintosh Plus, using DRAM with at least 150ns access speeds. The Macintosh SE followed with 120ns 30-pin SIMMs, and the entire Macintosh II family also used 120ns 30-pin SIMMs. (The Macintosh SE/30's RAM is similar to the Macintosh IIx and IIcx.) The first three Quadra models (700, 900. 950) used 80ns 30-pin SIMMs, but later Quadras used 72-pin SIMMs. Finally, the Classic used 150ns 30-pin SIMMs, and the Classic II, Color Classic, LC, and LCII used 100ns 30-pin SIMMs.
While RAM was interleaved with video processing for the earlier Macs, the Macintosh II family had dedicated video RAM (except for the IIci when using built-in video). The Mac Plus and SE had four SIMM slots, and most of the Macintosh II family had eight. While the memory throughput averaged 2.56MB/sec for the Plus and 3.22MB/sec for the SE, the Macintosh II family ranged from 12.53MB/sec to 60.69MB/sec.
Early SIMMs contained eight DRAM chips. Each SIMM had ten address pins and eight data pins, and each data pin is connected to one of the eight DRAM chips. The SIMMs are arranged in pairs; each pair is referred to as a row. Two SIMMs combined in a row provide a 16-bit-wide parallel data bus to the processor. Row one comprises SIMM 1 and SIMM 2, whereas row 2 comprises SIMMs 3 and 4.
Macintosh Quadras (and Mac SE/30) had SIMMs in four-slot banks for the 32-bit data bus. Also, later SIMMs used 4-bit (word) chips instead of 1-bit, reducing the number of chips on the SIMM board from eight to two.
When installing SIMMs into a Mac Plus or SE, keep in mind the following:
- On the Mac Plus, resistors 8 or 9 must be cut or installed to set the memory size
- On early Mac SEs, resistors 35 or 36 must be cut or installed to set the memory size
- On the later Mac SEs, a jumper above the SIMM slots sets the memory size
- SIMMs must be installed in pairs (creating a row)
- SIMMs in a row must match the size and access speed (at least 150ns)
- Larger SIMMs should be installed in row 1
For the Macintosh II family:
- SIMMs are installed in four-slot banks
- SIMMs in a bank must match the size and access speed (at least 120ns)
- Larger SIMMs should be installed in bank A (except for the Mac IIci)
- SIMMs in the Mac IIci and IIfx must be 80ns or faster (IIci requires fast page mode)
- The Mac IIci and Mac IIfx support optional cache cards that speed up RAM access
- Special models of the Mac IIfx and Mac IIci can utilize RAM parity checks
- The Mac IIfx has special 64-pin SIMM sockets
- The Mac IIsi had 1MB on its logic board (bank A), with four slots for bank B
- The Mac IIvx and IIvi had 4MB on the logic board and a four-slot bank B
For the Macintosh SE/30:
- SIMMs are installed in four-slot banks
- Bank A is closest to the motherboard edge, and Bank B is behind it
- Generally, install larger SIMMs in Bank A; however, experience shows there are two exceptions:
(1) for 17MB of total RAM, you must put 256K SIMMs into Bank A with 4MB SIMMs into Bank B
(2) when using 16MB SIMMs, put smaller capacity SIMMs into Bank A, with 16MB SIMMs into Bank B
- You can achieve 128MB of RAM by using 16MB SIMMs in all 8 SIMM slots
- SIMMs must be 120ns or faster
For the Macintosh Quadra family:
- Like the Macintosh II family, the 30-pin Quadra family used four-slot banks
- The Quadra 700 had 4MB of DRAM on its logic board (bank A)
- Install four matching SIMMs in the Quadra 700, 900, and 950
- The Quadra 800 had 8MB of DRAM on its logic board (bank A)
- The Quadra 800 appears to support SIMMs installed in any configuration
- Memory interleaving was supported on the Quadra 800 when like SIMMs were paired
- 8MB and 16MB SIMMs were supported on the Quadra family (32MB for the 800)
For the Macintosh LC family:
- The LC has 2MB of DRAM on its logic board, and the LC II could have 4MB
- The LC and LCII required two SIMMs of the same size
- Unusually, the LC accepts SIMMs with different access speeds
For the Macintosh Classic family:
- The Classic has 1MB preinstalled, the Classic II has 2MB, and the Color Classic had 4MB
- A Memory Expansion Board (with 1MB installed) was required for the Classic
- Like the later Mac SEs, a jumper was used to configure the Classic's memory
- The Classic supported 150ns SIMMs, but the II and Color Classic required at least 100ns
- 1-bit (or word) DRAM is recommended for the Classic (8-chip SIMMs)
Apple discouraged the use of composite SIMMs. The obscure composite SIMM uses lower-density components to construct a bank of memory. Composite SIMMs were often densely packed with DRAM chips on both the front and back of the board. However, not to be confused with composite practices, such density was common and acceptable with later non-composite 16MB SIMMs.
DRAM IC Identification Guide
Manufacturer / Product Family* / Word Width / Technology* / Density / Package* / Speed
* Usage varies
Manufacturer Codes
AMD - AM
AT&T - M
Dense-Pac - DPD
Fujistu - MB
Goldstar - GM
Hitachi - HM
Hyundai - HY
Micron - MT
Mitsubishi - M5M
Motorola - MCM
Mostek - MK
NEC - UPD/MC
NMB Technologies - AAA
Oki - MSM
Panasonic - MN
Samsung - KM
Siemens - HYB
Sharp - LH
Texas Instruments - TMS
Toshiba - TMM/TC
Toyocom - TH
Vitelic - V
Product Family Codes (usage varies)
Word Width
1 = 8 ICs equal SIMM capacity
4 = 2 ICs equal SIMM capacity
Technology (usage varies)
Blank = NMOS
C = CMOS
Density (note the overlap between 1MB and 4MB labeling)
256 = 256K
100 = 1MB
400 = 1MB
1024 = 1MB
(2MB modules use four 4-word width 1MB density ICs)
400 = 4MB
4000 = 4MB
4100 = 4MB
4100 = 4MB
6100 = 16MB
6400 = 16MB
Package (usage varies)
Speed
120 = 120ns
12 = 120ns
100 = 100ns
10 = 100ns
80 = 80ns
08 = 80ns
8 = 80ns
70 = 70ns
07= 70ns
7 = 70ns
60 = 60ns
06 = 60ns
6 = 60ns
Over its timespan, 30-pin SIMMs were produced in 256K, 1MB, 2MB, 4MB, and 16MB capacities. The pin arrangement limited the maximum number of addressable RAM to 16MB. This limitation led to the development of the 72-pin SIMMs, which were commonly used throughout the 1990s.
Apple began incorporating 30-pin SIMMs with the Macintosh Plus, using DRAM with at least 150ns access speeds. The Macintosh SE followed with 120ns 30-pin SIMMs, and the entire Macintosh II family also used 120ns 30-pin SIMMs. (The Macintosh SE/30's RAM is similar to the Macintosh IIx and IIcx.) The first three Quadra models (700, 900. 950) used 80ns 30-pin SIMMs, but later Quadras used 72-pin SIMMs. Finally, the Classic used 150ns 30-pin SIMMs, and the Classic II, Color Classic, LC, and LCII used 100ns 30-pin SIMMs.
While RAM was interleaved with video processing for the earlier Macs, the Macintosh II family had dedicated video RAM (except for the IIci when using built-in video). The Mac Plus and SE had four SIMM slots, and most of the Macintosh II family had eight. While the memory throughput averaged 2.56MB/sec for the Plus and 3.22MB/sec for the SE, the Macintosh II family ranged from 12.53MB/sec to 60.69MB/sec.
Early SIMMs contained eight DRAM chips. Each SIMM had ten address pins and eight data pins, and each data pin is connected to one of the eight DRAM chips. The SIMMs are arranged in pairs; each pair is referred to as a row. Two SIMMs combined in a row provide a 16-bit-wide parallel data bus to the processor. Row one comprises SIMM 1 and SIMM 2, whereas row 2 comprises SIMMs 3 and 4.
Macintosh Quadras (and Mac SE/30) had SIMMs in four-slot banks for the 32-bit data bus. Also, later SIMMs used 4-bit (word) chips instead of 1-bit, reducing the number of chips on the SIMM board from eight to two.
When installing SIMMs into a Mac Plus or SE, keep in mind the following:
- On the Mac Plus, resistors 8 or 9 must be cut or installed to set the memory size
- On early Mac SEs, resistors 35 or 36 must be cut or installed to set the memory size
- On the later Mac SEs, a jumper above the SIMM slots sets the memory size
- SIMMs must be installed in pairs (creating a row)
- SIMMs in a row must match the size and access speed (at least 150ns)
- Larger SIMMs should be installed in row 1
For the Macintosh II family:
- SIMMs are installed in four-slot banks
- SIMMs in a bank must match the size and access speed (at least 120ns)
- Larger SIMMs should be installed in bank A (except for the Mac IIci)
- SIMMs in the Mac IIci and IIfx must be 80ns or faster (IIci requires fast page mode)
- The Mac IIci and Mac IIfx support optional cache cards that speed up RAM access
- Special models of the Mac IIfx and Mac IIci can utilize RAM parity checks
- The Mac IIfx has special 64-pin SIMM sockets
- The Mac IIsi had 1MB on its logic board (bank A), with four slots for bank B
- The Mac IIvx and IIvi had 4MB on the logic board and a four-slot bank B
For the Macintosh SE/30:
- SIMMs are installed in four-slot banks
- Bank A is closest to the motherboard edge, and Bank B is behind it
- Generally, install larger SIMMs in Bank A; however, experience shows there are two exceptions:
(1) for 17MB of total RAM, you must put 256K SIMMs into Bank A with 4MB SIMMs into Bank B
(2) when using 16MB SIMMs, put smaller capacity SIMMs into Bank A, with 16MB SIMMs into Bank B
- You can achieve 128MB of RAM by using 16MB SIMMs in all 8 SIMM slots
- SIMMs must be 120ns or faster
For the Macintosh Quadra family:
- Like the Macintosh II family, the 30-pin Quadra family used four-slot banks
- The Quadra 700 had 4MB of DRAM on its logic board (bank A)
- Install four matching SIMMs in the Quadra 700, 900, and 950
- The Quadra 800 had 8MB of DRAM on its logic board (bank A)
- The Quadra 800 appears to support SIMMs installed in any configuration
- Memory interleaving was supported on the Quadra 800 when like SIMMs were paired
- 8MB and 16MB SIMMs were supported on the Quadra family (32MB for the 800)
For the Macintosh LC family:
- The LC has 2MB of DRAM on its logic board, and the LC II could have 4MB
- The LC and LCII required two SIMMs of the same size
- Unusually, the LC accepts SIMMs with different access speeds
For the Macintosh Classic family:
- The Classic has 1MB preinstalled, the Classic II has 2MB, and the Color Classic had 4MB
- A Memory Expansion Board (with 1MB installed) was required for the Classic
- Like the later Mac SEs, a jumper was used to configure the Classic's memory
- The Classic supported 150ns SIMMs, but the II and Color Classic required at least 100ns
- 1-bit (or word) DRAM is recommended for the Classic (8-chip SIMMs)
Apple discouraged the use of composite SIMMs. The obscure composite SIMM uses lower-density components to construct a bank of memory. Composite SIMMs were often densely packed with DRAM chips on both the front and back of the board. However, not to be confused with composite practices, such density was common and acceptable with later non-composite 16MB SIMMs.
DRAM IC Identification Guide
Manufacturer / Product Family* / Word Width / Technology* / Density / Package* / Speed
* Usage varies
Manufacturer Codes
AMD - AM
AT&T - M
Dense-Pac - DPD
Fujistu - MB
Goldstar - GM
Hitachi - HM
Hyundai - HY
Micron - MT
Mitsubishi - M5M
Motorola - MCM
Mostek - MK
NEC - UPD/MC
NMB Technologies - AAA
Oki - MSM
Panasonic - MN
Samsung - KM
Siemens - HYB
Sharp - LH
Texas Instruments - TMS
Toshiba - TMM/TC
Toyocom - TH
Vitelic - V
Product Family Codes (usage varies)
Word Width
1 = 8 ICs equal SIMM capacity
4 = 2 ICs equal SIMM capacity
Technology (usage varies)
Blank = NMOS
C = CMOS
Density (note the overlap between 1MB and 4MB labeling)
256 = 256K
100 = 1MB
400 = 1MB
1024 = 1MB
(2MB modules use four 4-word width 1MB density ICs)
400 = 4MB
4000 = 4MB
4100 = 4MB
4100 = 4MB
6100 = 16MB
6400 = 16MB
Package (usage varies)
Speed
120 = 120ns
12 = 120ns
100 = 100ns
10 = 100ns
80 = 80ns
08 = 80ns
8 = 80ns
70 = 70ns
07= 70ns
7 = 70ns
60 = 60ns
06 = 60ns
6 = 60ns
