NOTE: Tricia told me that this starts out a bit too technical, but gets better toward the end (so hang in there).
I've had in mind to do a technical post on computer memory for quite some time. Last week John gave me the push I needed to get it done. He sent me and Francois a link (http://www.toxicjunction.com/
Okay, back to my story.
Their comparison cries out for a response, so here it is. Comparing 25 -year-old brown spinning media to recent solid state "flash" memory is like comparing a warehouse to a pickup truck. This isn't a realistic pairing. The SD card (and half-sister "thumb" drives, etc.) is more a replacement for floppy disks rather than mainframe DASD (direct access storage device).
A point to compare: the speed difference. Disk I/O service time is measured in milliseconds (1/1000 or 0.001 .aka. thousandths of seconds ms). Internal random access memory (RAM) reference time is measured in nanoseconds (1/1000000000 or 0.000000001 .aka. billionths). To soften that blow (the million to one performance difference), I will point out that memory references are in bytes (typically 8 or 16 at a time), disk I/O is done in blocks of at least 128 bytes and more typically 2K or 4K and sometimes much more than that. These devices are not designed for single byte access. And that's where buffering and/or caching come in - to mitigate the drastic speed differences between disk and memory. SD memory access time is around 25µs (micro seconds or 0.000001) for first access and cycles of 50 ns for subsequent cycles.
Okay, now for my memory comparison:
This picture is of 2 memory modules. The large one is a 4MB memory board from a VAX-8600 circa 1986-1990. Next to it is a micro SD card. This one is only 2GB but it could just as easily be 16GB (I don't think 32GB micro SD cards are out yet). In case you don't know this, you can click on the picture for a close-up view.
Okay, now for some statistics:
The 4MB board is 12" x 15.5" x 0.25" and weighs 2 lb 8.5 oz.
The micro SD is 0.43" x 0.6" x 0.032" (11mm x 15mm x 0.82mm). My postal scale measures in 0.1 ounce increments and the micro SD doesn't register on it (nor does a standard SD card).
16GB / 4MG = 4096
So,
4096 x .25" = 1024" = 85.333'
4096 x 40.5 oz. = 165,888 oz = 10, 368 lb. = 5.184 tons
In other words, it would require 4096 of the 4MB boards to hold the same amount of information as a 16GB micro SD.
If you were to get 4096 of these boards and stack them up, it would be 85' 4" tall and weigh over 5 tons.
Now, for the rest of the story: pricing
As for cost, the 16GB micro SD cards are selling on eBay for $50-60 including shipping, although 8GB micro SD's are going for under $20 (get 2 8's for about $35).
My 1990 price list does not have the 4MB VAX 8600 memory board (the one in my photo). It was already obsolete by 1990; it was new in 1986. The book does have a 64MB board listed for $50,400 and a 256MB board was $434,000. So, based on ever decreasing memory prices (on a per-megabyte basis in those days), I'm going to estimate that the 1986 list price of this 4MB board was probably around $10,000.
So, based on that estimate, in 1986, 16GB of silicon based computer memory would have cost:
4096 x $10,000 = $40,960,000.00
Disclaimer: The more techno savvy of you may point out that comparing RAM and a micro SD card is not quite valid either. You're probably right. This is more like comparing a Porsche 911 Turbo Carrera and a VW Beatle.
