# What do memory configurations like “256Kx18” mean?

This is a beginner question here. When choosing memory ICs, one of the options is the memory size/configurations. I understand the size part, but what does the "16Kx9" mean? It seems the same memory size is usually available in different configurations. I attached a screenshot from Digikey as an example.

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What hasn't been mentioned in the answers yet: if the configuration is some multiple of 9, it generally means that you're dealing with some combination of 8 bit bytes and 1 bit parity. – Robert Harvey Mar 7 '14 at 20:36
Usually, although there is no requirement to use it in that manner. – Ignacio Vazquez-Abrams Mar 7 '14 at 23:02
that's good point. thanks guys for your great answers - good karma :) – wildwildwilliam Mar 13 '14 at 19:26

## 2 Answers

256K x 8 means 256 kibi-locations, each location holding 8 bits. There are 18 address lines (218 = 256 * 1024) and 8 data lines.

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16k x 9 means that the memory chip has a total of 16k locations in which it can store a binary number that consists of 9 bits. It will have a 14 bit address structure (14 bit gives you 16,384 locations in decimal). It may be a serial device but the address lines will still be there but internal to the device.

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When you say it will have a 14-bit address structure, is this a common property of all memory or is it derived from the aforementioned 16k x 9 notation? – JYelton Mar 7 '14 at 21:29
@JYelton $2^{14}$ = 16,384 and 16k (binary speak) is 16,384 and uses 14 address lines. Not sure I've answered your question? – Andy aka Mar 7 '14 at 21:38
I see it now, it's a matter of taking the number of locations (16k, which is 16,384) and knowing to what power 2 is raised to arrive at that figure. I was missing that, which made it seem like you magically came up with the number 14. :) – JYelton Mar 7 '14 at 21:49
@JYelton a pleasure to help you sir! – Andy aka Mar 7 '14 at 21:50