Correct me if I've messed up:
HDs stream data at about 33 megabytes per second or faster. 100 M in 3 seconds. 500 M in 15 seconds. So we have some serious overhead to get up to 250 seconds. (1/16 speed?) I wonder what that is?
When disk compression was the rage many years ago, it was generally accepted that the time saving from loading smaller files outweighed the decompression time. Both HDs and processors are far faster today, but processors must have outdone HDs tremendously. For text, the compression factor was 1/10 to 1/20, I believe. The compression for programs was about 1/2. Already compressed files, like jpg, mpg, divx, mp3, and zip, are practically uncompressible. However some of the compression comes from allocating disk blocks with less waste, so small compressed files may show some compression from that.
For a few years W9x had compressed volumes (drvspace, dblspace) built in, but it was phased out and dropped, as HD size outpaced file sizes. (MS paid the major company, Stacker, that developed the compression method MS "imitated", a huge settlement, the greatest windfall that company ever experienced considering that disk compression was worthless within a year or two.)
The primary objection to disk compression was data corruption. The exact cause was undetermined, but people began to shun compression just when it became mainstream. One problem was that the pieces of different files were combined in the same allocation block to eliminate slack. (Slack is the unused space in the last allocation block.) Maybe files were cached too long for that reason, leaving them more subject to not being written to disk during crashes and lockups.
Another oddity was that the reported free space was complete BS, especially when the drive got, say, 80% full. You would see all this space left, write a few small files, and suddenly be out of space. The reported compression rate was partly BS too. The base uncompressed size was not the size of the files added together, but the amount of space it would take to store the files on a volume of twice the HD size, and therefore double the slack.