512 DDR3 but the chip is 4gb DDR3. Why?

[Mike Larsen]

I've been looking into the chips used with the BBB and I'm curious about something.

Why do you use a 4gb chip and employ only 512mb of it? 

Is the extra space used for anything?

The hardware manual says that other DDR3L chips may be used...I'm assuming it needs to be a x16...but what other pitfalls should I watch out for?

[Robert Nelson]

Memory manufactures market their ic's using "Megabit (Mb)"...

4 (Mb) * 1024 / 8 = 512 (MB) Megabyte

Regards,

--
Robert Nelson
http://www.rcn-ee.com/

[Robert Nelson]

Doh! that should be "Gb" but the math Gb->Mb transition is still correct..

[Peter Baltus]

Could it be because 4 Gbit translates nicely into 512Mbyte? ;-)

Best regards,

Peter

[Mike Larsen]

I'm missing something and I do greatly apologize for my ignorance. The RAM module MT41K256M16 used on the BBB is a 512mb stick and not a 4gb? I see the 32mb x 16bit x 8 banks yields 4096...what am I missing?

Please humor me, I've been cramming for college finals and have very little mental RAM resources available right now.

[Robert Nelson]

On Fri, Dec 12, 2014 at 12:16 PM, Mike Larsen <touch.o...@gmail.com> wrote:
> I'm missing something and I do greatly apologize for my ignorance. The RAM
> module MT41K256M16 used on the BBB is a 512mb stick and not a 4gb? I see the
> 32mb x 16bit x 8 banks yields 4096...what am I missing?

4Gb = 512MB

> Please humor me, I've been cramming for college finals and have very little
> mental RAM resources available right now.

Mega"bit" vs Mega"byte"...

[Mike Larsen]

Thank you, sir. My understanding has been bolstered by your patience and insight.

Happy holidays.

~M