Re: Large RAM sizes in embedded systems


larwe wrote:
I'd be curious to hear from anyone who has worked on embedded systems
with relatively large amounts of directly-addressable RAM.

I'm discussing with a colleague/client an application that would work
on a nominally 740GB data set. The nature of the data and the required
processing is such that it's a "must-have" performance improvement to
hold the entire data set in RAM rather than swapping in from some
secondary storage mechanism. It's perfectly acceptable for the machine
to take an entire week to cold-boot. It's not acceptable, once booted,
for it to wait several seconds to page in data from a hard disk :)


Let us assume for a moment that you have access to
the best chips, layouts and bank accounts.

You can build it with 24 modules of 32G each.

Each module consists of 128 512M x 4 DDR2 SDRAM.
Namely, 15 row/col addresses and 3 bank pins.
You can buffer/share the address pins,
but need individual bank pins (or 128x3=384 pins).
So, each modules require a 500 pins FPGA.

24 of 16 layers 8"x11" PCB
24 of 500 pins FPGA
3072 of 512M x 4

Assume that you can get the FPGA for $50 and SDRAM for $5 each,
it can be build for approxmately $20,000, give or take a few K.

.

Relevant Pages

  • Re: Large RAM sizes in embedded systems
    ... systems with relatively large amounts of directly-addressable RAM. ... I'm discussing with a colleague/client an application that would ... work on a nominally 740GB data set. ... in from some secondary storage mechanism. ...
    (comp.arch.embedded)
  • Re: Large RAM sizes in embedded systems
    ... with relatively large amounts of directly-addressable RAM. ... on a nominally 740GB data set. ... Is there some way to frame up the data access patterns? ... A hard drive array will have no problem to BEGIN serving up a purely ...
    (comp.arch.embedded)