usb - How does a hard drive compare to Flash memory working as a hard drive in terms of speed?

Some experiment I did with hard drive read/write speed was 10MB/s write and 40MB/s read, and with a USB Flash drive, it can be 5MB/s write and 10MB/s read.

Also, if I put a virtual hard drive .vhd file in a hard drive or in a USB Flash drive and try a Virtual Machine using it, the one using the hard drive is quite fast, while the one using the USB Flash drive is close to not usable.

So I wonder some early netbooks use 4GB or 8GB flash memory as the hard drive, and even the Apple Mac Air has an option of using flash memory instead of a hard drive. But in those situation, will the speed be slower than using a hard drive, like in the case of a USB Flash drive?

Answer

One big difference is that the flash drive is using the USB bus, while the drive is using the SATA bus. So even if your flash memory was the same speed in both cases, the drive would have a higher potential throughput.