RK05/f is a hard disk drive, that was used among others at the PDP8/e system. If you think that there are now 8 GB Micro-SD cards (1mmx7mm4mm) its pretty amazing to see this box, that is bigger and with more weight than an common microwave and can only store 5 Mb data. But at this time, 5 Mb were an amazing storage size!
The letter 'f' in the model name stands for "fix", it means, its not a removable hard disk (Yeah, removeable hard disks exists at this time too, but not so handy as the acutal ones!)
Because the disk was not removeable, there were less mechanical problems ahead, with track alignment for instance, so the fixed version was able to store 5 MB, the removable version was limited to 2.5 MB.
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