My first "big" hard drive was a 10 Mbyte drive with one fixed and one removable 17" platter. Each side was 2.5Mbyes and I thought I had the world of storage. The drive was 10.5" tall by 19" wide and about 30" long and weighed close to 130 pounds. It cost over $10,000 plus the controller for the DEC compatible computer box made by Heathkit. The 2.5 Mbyte size was the same size as the Digital Equipment Corp (DEC) 2.5 MB RK-05. The DEC RL-01 was 5 MB and the RL-02 was 10MB with the same diameter platters. These initially were also north of $10k drives.
The DEC PDP-11/38 had 256 Kbytes or ram. We ran 16 terminals, four parallel printers and had a 10,000 item inventory with point of sale software. The VT-100 terminals could switch between the Dibol language POS software, word processing and spreadsheets.
The last iteration of the dual sized DEC PDP-11 CPU card could support the dual sized 4 MBYTE memory card that cost $2,000. The 32Kbyte dual memory card was $2,000 and each doubling of size cost $2,000 64K - 128K - 256K - 512K - 1Mega byte - 2 MB - 4 MB. I used 2.5 MB of the 4 MB memory as the same size as the RK05 as the swap disc for compiling Dibol code. It was really fast.
The Seagate ST-05 was a 5 MB Winchester drive (non removable platter and sealed against dust) and was called a 5" hard drive. It was a sealed unit like the 3.5" drives of today. The drive cost $1,500 and the controller for my Heathkit computer cost $1,500.
We paid dearly for storage in the late 70s and early 80s.