how many RAM chips would you need for ...?

[knavely]

so i have this assignment, and one of the questions is:
how many 512k x 16 RAM chips would you need for a 64M x 64 RAM chip?

my notes are really spotty kinda having trouble..

but i know that 512K = 2^10 * 2^9 = 2^19

so there are 19 address lines per chip

and we need to make that into 26
64 = 2^6 * 2^20 = 2^26

so if i use 2 chips i will have enough address lines, but the word size...
this is where my notes are failing me, not sure what to do.

[bwkaz]

512K words of 16 bits (2 bytes) each = 1 megabyte of memory.

64M words of 64 bits (8 bytes) each = 512 megabytes of memory.

Make sense now?

Alternatively, think of it this way:

If your 512Kx16 chips have 19 address lines (and they do), you'll need 7 extra chip-select lines that will ACT as address lines to the outside hardware to make 26. So you'd have 2 ^ 7 chips. But since the 64M chip has words that are four times the size of the 512Kx16 chips, you'll need 4 times that number of chips -- every address coming in on the 26 lines will actually address 4 512K chips. You come to the same answer.