Quadra 605 

Physical Memory: 4MB soldered on.  256K and 512K 
SIMMs will not work. The 605 uses a 72-pin SIMM that is 
different from the standard used in previous Mac models.  
Under 24-bit addressing, up to 8MB can be installed using a
4MB SIMM. Under 32-bit addressing, up to 36MB could be 
installed using a 32MB SIMs. The SIMM slot accepts a 4, 
8, 16, or 32MB SIMM.

Extended Memory: The 68040 CPU in the 605 has a 
built–in Memory Management Unit. Therefore, the 605 can 
run RAM Doubler or virtual memory without requiring any 
additional hardware. In 24–bit mode, the 605 can address 
up to 13MB of VM, and in 32–bit mode, it can address up to 
1024MB. We recommend RAM Doubler.

Video RAM:  Two expansion slots are available for a maximum of 1MB video RAM. The 605 can use 80ns or faster video RAM.

Quadra/Centris 610 

Physical Memory: 4MB soldered on.  256K and 512K 
SIMMs will not work. The 610 uses a 72-pin SIMM that is 
different from the standard used in previous Mac models.  
Under 24-bit addressing, up to 8MB can be installed using 
2MB SIMMs. Under 32-bit addressing, up to 68MB could be 
installed using two 32MB SIMMs. The SIMM slots accept 4, 
8, 16, or 32MB SIMMs.

Extended Memory: The 68040 CPU in the 610 has a 
built–in Memory Management Unit. Therefore, the 610 can 
run RAM Doubler or virtual memory without requiring any 
additional hardware. In 24–bit mode, the 610 can address 
up to 13MB of VM, and in 32–bit mode, it can address up to 
1024MB. We recommend RAM Doubler.

Video RAM: 512K soldered–in (enough to support 8–bit color on a 13" monitor). Two expansion slots are available for a maximum of 1MB video RAM. The 610 can use 80ns or faster video RAM.

The only difference between the Centris 610 and the Quadra 610 is the processor speed - the Centris runs at 20 MHz while the Quadra runs at 25 MHz.

Quadra 630 

Physical Memory: 4MB soldered on.  Under 24-bit 
addressing, up to 8MB can be installed using a 4MB SIMM. 
Under 32-bit addressing, up to 36MB could be installed 
using a 32MB SIMM.

Extended Memory: The 68040 CPU in the 630 has a 
built–in Memory Management Unit. Therefore, the 630 can 
run RAM Doubler or virtual memory without requiring any 
additional hardware. In 24–bit mode, the 630 can address 
up to 13MB of VM, and in 32–bit mode, it can address up to 
1024MB. We recommend RAM Doubler.

Video RAM:  1MB of 80ns DRAM is soldered on, which can 
support 16-bit color on a 14" monitor.

Quadra/Centris 650 

Physical Memory:  The 650 is available with 8MB soldered 
on. The SIMM slots accept 1, 2, 4, 8, 16, or 32MB SIMMs, 
for a maximum of 136MB. To address large amounts of 
RAM, use System 7 standard 32–bit addressing. The 650 
uses a 72-pin SIMM that is different from the standard used 
in previous Mac models.

Extended Memory: The 68040 CPU in the 650 has a built–
in Memory Management Unit. Therefore, the 650 can run 
RAM Doubler or virtual memory without requiring any 
additional hardware. In 24–bit mode, the 650 can address 
up to 13MB of VM, and in 32–bit mode, it can address up to 
1024MB. We recommend RAM Doubler.

Video RAM: 512K soldered–in (enough to support 8–bit 
color on a 13" monitor). Two expansion slots are available for a maximum of 1MB video RAM. The 650 can use 80ns or faster video RAM.

The only difference between the Centris 650 and the Quadra 650 is the processor speed - the Centris runs at 25 MHz while the Quadra runs at 33 MHz.

Quadra/Centris 660av 

Physical Memory: 4MB soldered on and one 4MB SIMM. 
256K and 512K SIMMs will not work. The SIMM slots
accept 4, 8, 16, or 32MB SIMMs.  Up to 68MB could be 
installed using two 32MB SIMMs. The 660av uses a 72-pin 
SIMM that is different from the standard used in previous 
Mac models.

Extended Memory: The 68040 CPU in the 660av has a built–
in Memory Management Unit. Therefore, the 660av can run 
RAM Doubler or virtual memory without requiring any 
additional hardware. In 32–bit mode, it can address up to 
1024MB. We recommend RAM Doubler.

Video RAM: 1MB soldered–in.

There is no difference betwen the Centris and Quadra 660 av besides the label on the outside.  In fact, installing the Quadra enabler in the Centris machine will result in the "About This Macintosh" showing "Quadra 660 av."

Quadra 700 

Physical Memory: 256K and 512K SIMMs will not work.  Up 
to 68MB could be installed using four low profile 16MB 
SIMMs. However, the placement of the SIMM slots 
underneath the hard drive means that standard composite 
16MB SIMMs will not fit. To address large amounts of RAM, 
use System 7 standard 32–bit addressing. The bank may 
either be empty, or filled with four SIMMs which must all be 
of the same size.

Extended Memory: The 68040 CPU in the Quadra 700 has 
a built–in Memory Management Unit. Therefore, the Quadra 
700 can run RAM Doubler or virtual memory without 
requiring any additional hardware. In 24–bit mode, the 
Quadra 700 can address up to 13MB of VM, and in 32–bit 
mode, it can address up to 1024MB. We recommend RAM 
Doubler.

Video RAM: 512K soldered–in (enough to support 8–bit color on a 13" monitor). 6 additional sockets in 3 banks for a maximum of 2MB. The sockets are for special 68–pin 256K (only) SIMMs. Many people add one pair of 256K video SIMMs to have enough memory to support 24–bit color on a 12" monitor. These 256K SIMMs are the same video SIMMs that are factory installed on the LC. The 700 can use 80ns or faster video RAM.

Quadra 800 

Physical Memory: 8MB soldered on.  Up to 136MB could be 
installed using four 32MB SIMMs. The SIMM slots accept 4, 
8, 16, or 32MB SIMMs. The 800 uses a 72-pin SIMM that is 
different from the standard used in previous Quadra models.
 To address large amounts of RAM, use System 7 standard 
32–bit addressing.

Extended Memory: The 68040 CPU in the Quadra 800 has 
a built–in Memory Management Unit. Therefore, the Quadra 
800 can run RAM Doubler or virtual memory without 
requiring any additional hardware. In 24–bit mode, the 
Quadra 800 can address up to 13MB of VM, and in 32–bit
mode, it can address up to 1024MB. We recommend RAM 
Doubler.

Video RAM: 512K soldered–in (enough to support 8–bit color on a 13" monitor). Two expansion slots are available for a maximum of 1MB video RAM. The 800 can use 80ns or faster video RAM.

Quadra 840av 

Physical Memory: The 840av uses a 72-pin SIMM that is 
different from the standard used in previous Mac models. 
Up to 128MB could be installed using four 32MB SIMMs. 
The SIMM slots accept  4, 8, 16, or 32MB SIMMs. 

Extended Memory: The 68040 CPU in the Quadra 840av 
has a built–in Memory Management Unit. Therefore, the 
Quadra 840av can run RAM Doubler or virtual memory 
without requiring any additional hardware. In 32–bit mode, 
it can address up to 1024MB. We recommend RAM 
Doubler.

Video RAM: 1MB soldered–in. Four expansion slots are 
available for a maximum of 2MB video RAM. The 840av 
can use 80ns or faster video RAM.

Quadra 900/950 

Physical Memory: Does not support 256K or 512K SIMMs. 
To address more than 8MB, 32–bit addressing must be On. 
Using a Quadra 900 with less than 16MB is somewhat 
unusual.  Up to 256MB can be installed using 16MB SIMMs.
All SIMMs in all banks must be the same speed. The layout 
of the banks is unusual: Bank A is the left two sockets of the 
upper row of 8 sockets plus the left two sockets of the lower
row of 8, similarly for B, C, and D. The Quadra 900 and 950 
have almost identical memory configurations (see video 
RAM). If composite 16MB SIMMs are used, special low–
profile versions are required at least for the lower two 
sockets of Bank D (motherboard clearance space limitation).
Use System 7 standard 32–bit addressing. Some 16MB 
SIMMs that are compatible with the 900 may not work 
properly on the 950.

Extended Memory: The 68040 CPU in the Quadra 900 has a built–in Memory Management Unit. Therefore, the Quadra 900 can run RAM Doubler or virtual memory without requiring any additional hardware. In 24–bit mode, the Quadra 900 can address up to 13MB of VM, and in 32–bit mode, it can address up to 1024MB. We recommend RAM Doubler.

Video RAM: The 900 and 950 have identical hardware, but the 950 uses a more sophisticated interleaving technique, which allows it to get more out of the same amount of video RAM. For example, the standard 1MB soldered on the 900 is enough to support 24–bit color on a 12" monitor but it gives 24–bit color on a 13" monitor on the 950. There are four sockets in two banks of two each. Sockets are for special 68–pin 256K (only) SIMMs. These are the same video SIMMs that are factory–installed on the LC. The 900 can use 100ns video RAM, but the 950 requires 80ns.