Kind of an off-the-wall computer question

[jmatt]

This came up at work and no one knew the answer (things are slo-o-o-o-ow today...).

Does anyone know why floppies were 8", then 5-1/4" then 3-1/2"? Not the size change due to technology improvement, but why were those sizes chosen/used?

Told you it was off-the-wall....

 

[Fanny McLonghorn]

They didn't actually have anything to measure the discs when they first started making them, so they used cups that they found around the office. In another five years, we'll have the shot disc.

 

[VacantlyOccupied]

The switch from 8-inch to 5.25 inch diskettes was for a very scientific reason:

In reply to:

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[Hayden_Horn]

that is badass.

 

[MrPhlegm]

and the 3.5" ones are that size so that they will fit into a shirt pocket along with a pocket protector and 15 pens.

The reason they started out 8" is because that is how big IBM had to make them to hold 100K due to the low storage density of magnetic media at the time. IBM needed 100K to hold the microcode for their mainframes.

The microcode ran between the hardware and the operating system and made whichever model of IBM mainframe look like an BM 360 or IBM 370 to the OS no matter what the native machine code was.

It was a big breakthrough because befor the 360 series every different model of a mainframe had to have a custom OS that knew the machine code of the particular model of machine it was written for. This was a royal pain in the *** because if you wanted to upgrade to a faster bigger machine you had to convert all of your programming to interface with the new operating system at great expense.

When IBM brought out the 360 series you could start out with a baby 360 and upgrade to larger and larger 360's just by backing up your system and data, unplugging the little 360 and hauling it away and plugging in one of it's big brothers and reloading your system and data and IMPLing and IPLing and away you would go with hardly a break in the action. It was brilliant and the reason IBM dominated the computer world for so long.

To Cold Boot an IBM 360 or 370 (actually I am only sure of this for the 370 series as I never worked on a 360) you would first IMPL (Initial Micro Program Load) the microcode and the bootstrap loader (I don't remember what IBM called the bootstrap loader) on the 8" floppy that was in the floppy drive in the console, then you would load the actual OS (MFT, MVT, VS1, VS2, or VM) with an IPL (Initial Program Load) that would read the OS off of tape or disk.

Basically that is the way computers work today, the bios is the microcode and bootstrap loader, it loads first from the cmos or rom and then the OS loads. The OS never actually talks to the chip it talks to the BIOS and the BIOS talks to the chip.

This stuff has come a hell of a long way since I first got introduced to computers. The scary part of the whole thing is that the rate of change keeps growing exponentialy.