As processors are all going multi-core now, multi-threading is a must. My 4 core shows only ONE CPU being utilized during a 600MB 7zip decompression operation. This is on Windows Vista 32-bit.
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Actaully LZMA decompression is pretty fast for modern CPU: about 10 MB/s of compressed data + 20-30 MB/s of uncompressed data. So it's not too lower than speed of HDD.
Speeds are growed up, it's time to reincarnate this request.
https://sourceforge.net/p/sevenzip/discussion/45797/thread/71f8bd84/ some benchmarks and links are included. Today to achieve the maximum speed when unpacking big file that is one and lonely in archive we need multithreading. For the current condition on the lowest packing level (fastest) the speed limit is about 80 to 90MB/s (ramdisk and 4770K tested) I 've tested different algorithms and got even slower speeds. So it would be good to use at least two threads when unpacking big files, current speed limited by my system SSDs is 320/240 MB/s read/write speed. And yes, I want to unpack from one ssd to another.