An ancient lie that is no more?
January 5, 2012 9:26 AM   Subscribe

Are GBs given for SSD capacities actually GiBs (2^30 bytes each) or standard "hard disk GBs" (10^9 bytes each)?

I'm trying to transparently replace a 250 GB conventional laptop hard disk (this one) with an SSD (this one) tagged as "240 GB" and wondering whether it will be large enough to just copy the existing partition (fills entire drive) over byte-for-byte.

Will it be large enough to do this?
Bonus question: How likely is a byte-for-byte copy of the disk to result in an unchanged Windows XP system?
posted by themel to Computers & Internet (4 answers total) 2 users marked this as a favorite
From the SSD's page: "Consumers may see a discrepancy between reported capacity and actual capacity; the storage industry standard is to display capacity in decimal. However, the operating system usually calculates capacity in binary format, causing traditional HDD and SSD to show a lower capacity in Windows."

So, they seem to use the same convention.
posted by inigo2 at 10:03 AM on January 5, 2012

I would assume SSD capacities are are measured in GB (not GiB), but I'm not sure about that.

But I came into the thread to point out that you can resize NTFS partitions using something like gparted to make this work, even if the new drive is slightly smaller.

I've copied both XP and Windows 7 systems to new hard drives in the manner you describe, and they have both worked fine, assuming the new HD is using the same interface as the old one (SATA) and the machine's hardware isn't being otherwise changed.
posted by qxntpqbbbqxl at 10:11 AM on January 5, 2012

YMMV. You have to consider both the GiB vs GB naming convention, plus another variant that didn't really exist in HDDs. Many SSD manufacturers set the firmware to reserve some of the cells to actively replace failing or worn out cells on the SSD. It can be anywhere from 1-3% of the cells.

My personal example: I have a Mushkin Io 128GB SSD from early 2010 on the Indilinx Barefoot controller. When I connected it, it reported 117.9GiB available. The actual conversion of 128GB -> GiB results in 119.2GiB. 1% of the cells were reserved and therefore showed as unavailable.
posted by Mister Fabulous at 10:37 AM on January 5, 2012

When I connected it, it reported 117.9GiB available. The actual conversion of 128GB -> GiB results in 119.2GiB.

Formatting a disk reserves some space for file allocation tables and other filesystem record-keeping, so this doesn't really mean anything. It's like taking a 40'x40' space, building a house on it, and then complaining that you don't actually have 1600 sq. ft. of floor space. Your floor isn't less than 1600 sq. ft. because the space was mis-measured, it's smaller because the walls and counters and other things that are required for a house to exist are using some of it.
posted by tylerkaraszewski at 11:22 AM on January 5, 2012

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