How fast could you read/write to floppy disks, both 3 1/4 and 5 1/2?

Question

Does anyone know/remember the actual read/write speed of floppy disks? I want to use this as a tidbit for arguing how painfully slow our Sharepoint server is, but all the websites with information about the disks don't seem to have the actual speeds they worked at.

Heave

It depends on OS and hardware. I had a 4 MHz Z80 clone as PC and 5.25 floppy drives. Copying a 780k disk from one drive to the other took about 10 minutes. – Neil

Answer 1

IIRC,

The controllers at the end where rated 500kbps to 1Mbps for most modern floppy controllers older ones had about 250 kbps.

The actual disks always maxed out around 100-250kbps and I've never seen above 250kbps on a floppy.

Read speeds could reach higher but I've never seen close to a controllers max. Not the best answer perhaps but some insight for you.

Haslett

Thank you, that was the information I was looking for. Our sharepoint server is LITERALLY the speed of an average floppy disk. – Heave

Answer 2

Depends, in the late 1970s, an 8bit Intel 8271 Floppy disk controller, with an Intel 8257 DMA controller, operating in a machine clocked at say 1 MHz, and reading a 40 track, single sided, single density, 5.25", 3 KByte / track, disk, would incur a ~ 400ms spin up cost, as the drive accelerated from 0 to 300 rpm, before waiting the > 50ms necessary for the head to seek and settle on the desired track, to be able to have it initiate a sector operation, which would incur a ~ 60ms penalty, as the device waited for the desired sector to come under the head. Tracks were typically partitioned into 128, 256 or 512 byte sectors (blocks). So reading / writing a > 3 Kbyte file would incur over a second of spin up and seek overhead, before adding the cost of the bytes transferred, say 4-8ms per byte written. Two tracks having to be sought, and numerous sectors read, to assemble the file. So nowhere near achieving the 1 MByte / sec, the controllers were theoretically able to crunch.

Add the like of Commodore opting, in the early 1980s, in say their Commodore 1540/1 drives, to stick a 300 bits (37 bytes) per second, serial bus between the external disk drives and the computer, making 0.4 KBytes a second the theoretical maximum transfer rate. Atari opting for a slightly faster 2400 bits (300 bytes) / second serial controller, in the same period.

In the late 1980s High Density, double sided, 80 track, 360 rpm rated, 3.5" disks, notionally able to hold ~ 2MB, and typically partitioned into 512 byte sectors, would more than quadruple transfer rates, as seek times improved. The disks being physically smaller, requiring the heads to travel a smaller distance, and spun faster, to reduce sector seek operations, while still requiring less energy and time to be spin up. The larger sector sizes also reduced the number of individual block transactions, with the associated set-up costs. Though still nowhere near achieving the 1 MByte, even an 8 bit, 1 MHZ controller could in theory shift a second, let alone what could be pushed over the > 50 MByte / sec data buses, of the almost 32bit systems, the drives were sold with.

Grant

Actually, Commodore's 1541 was capable of around 300-400 bytes per second. I used to estimate the loading time of games by looking at the number of blocks and then counting that many seconds. The 1571 and 1581 were both quite a bit faster: roughly on a par with PC drives of the same capacity. – Shad

Answer 3

I definitely remember my first PC's hard drive topping out at a bit under 500KB/s, and the floppy drives were definitely much slower.

The one definitive answer I can give is that the IBM PC's floppy controller ran at 250Kbit/sec. This gives a speed of around 25KB/sec for floppy access on the original PC.

Shad