> Ok, explain to me...I took a 220MB system file and compressed it down to 28MB.
Must have had a lot of repeating data. Text files, etc... Also was that
220MB of allocated space or used space. I'd bet the former.
> Obviously this is lossless as I can recover individual files from
> within it that are things like extensions, fonts, etc.
> I admit, JPEG, MPEG, etc. are lossful, but modems have been doing
> v.42bis compression which is 4:1 on the fly for a long time now.
> Granted, the speed is only 53k at best (although some faster network
> equipment also uses a subset of v.42bis), so the time frame from
> receiving to sending would be larger that you would get with
> receiving to sending to local device like a tape drive.
The 4:1 assumed text. Transferring a binary file or especially a ZIPed
or .SIT file would crater that number down. Sometimes below 1:1 as the
simple processor in the modem tried to compress something using a text
oriented approach. In those cases the compression information overhead
would outweigh the limited savings, if any.
> I'm wondering if it would be possible for Retrospect to do some
> software compression that may be slower, but would allow greater
> inline compression. I would guess that the software compression
> built into Retrospect is the same algorythem that hardware
> compression drives use. By getting with a company like Alladin
> Systems, it would seem like they could improve on that technology.
A disk based compression has a major advantage over anything going to
tape. It can pre qualify individual files or even switch methods if
needed. With a tape drive you're in the position of having to keep the
drive buffers from emptying or you'd loose any advantage of the
compression. And you only get one try. Once the data is on the tape it's
gone and it would be a time disaster to rewind and switch methods.
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