[net.micro.mac] Cheap RAM upgrade

xxajtxx@hou2d.UUCP (A.THANGARAJ) (10/24/85)

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640K bytes of RAM is becoming more and more desirable on PC's today. The extra
RAM can be used as a RAMDISK, especially for floppy-disk PC models. (You can
zip along faster than a hard disk in some applications). Many programs these
days are memory-hungry and can use (or may need) a lot more than 256K bytes RAM.
Now that cheap RAM upgrades on the motherboard using high-density 256K chips
have become commonplace, it would be interesting to find out on just which
models of which computers it is feasible to do so. I would think that at least
two conditions need to be satisfied:
1. The motherboard should have sockets into which the high-density chips can be 
   inserted. For example, the motherboard might have 128K bytes of soldered
   memory and eighteen empty sockets for additional RAM. If you insert 18 
   low-density (ie. 64K-bit) chips, you will get another 128K bytes of RAM
   (2 of the 18 chips store parity bits; the remaining 16 chips make up 
   16X64/8 = 128K bytes of RAM). If, on the other hand, you insert 18 
   high-density (256K-bit) chips, you get another 16X256/8 = 512K bytes of RAM.
   If the motherboard comes with low density chips in the sockets, you can pull
   them out and replace them with high-density chips for under $60 total cost. 
   If all the RAM in the motherboard is soldered, and there are no empty 
   sockets for additional RAM, that particular model of that PC cannot be 
   cheaply expanded - you will need an expansion board.
2. Having put the extra memory in, you have to be able to tell the computer
   that it now has that extra memory. This usually involves changing the 
   settings of dipswitches on the motherboard. You have to know which 
   dipswitches to set and how to set them. If the PC manual doesn't tell you 
   that, you have to experiment, or ask a friend, etc., and it still may not
   work. 

I would like to hear from the net regarding which PC's (and which models)
have socketed RAM and support cheap RAM upgrades, and whether the dipswitch
(or other) settings required are mentioned anywhere. I will summarize and post
to the net.
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