OK, apologies for the confusion.
The 500GB storage in the previous screenshot is of the host computer running Linux mint.
The drive designated /dev/sda2 for 3.9 GB is also a partition on the host computer.(which I had mistakingly thought was the eMMC storage) Subsequently I put back the 320GB 2.5" HDD back into the Slice before I did the lsusb and here's what I got back.
What I think it is telling us is that the rpiboot program is either corrupt or not installed properly as I have tried several times to reinstall but the first time I got a fatal error of some sort as I was trying to clone from GitHub.com and then, each time after that, I got user name and password requests to attempt installation only to be met with more and more tasks in Linux for which I'm not equipped ???
I tried the automatic windows 7 installer which again I downloaded all the various programs, such as computemoduleboot only to find that it always hung and was never able to complete the scan or find and mount the so called mass storage drive on the eMMC. This is what led me to remove the internal (320GB) HDD of the Slice because for some reason I was unable to unmount or eject the drive in order to carry out the rest of the reflashing procedure.
So, in summary all this grief came about from what should have been a simple process of updating the OS in the first instance as I was not getting network connectivity???
Instead I've been plunged into a crash course on linux and all its foibles and not experienced any joy from my newly received device.