Stange peripherals… The 1581 diskdrive

Ok, it may not seem as exotic as the two previous peripherals discussed here (the Quick Data Drive and the Silicon Disk), but fact is, that the 1581 drive, did not have such a widespread use as the 1541 and the 1570/71 drives for the C64/128, making it a candidate for our weekly article in the series.

Back in the late 80’s, some C64 users tried to make use of the 1570/71 drives (which were intended for the C128 market) but could really only benefit from the increased disk-capacity as the C64 lacked the formidable serial bus which was to be found on the 128-models and which really augmented the power of the 1570/71 drives.
Great was the anticipation in 1987 when Commodore released the 1581 drive onto the market.  Would it finally be the powerdrive for the C64 comunity or would it be an expensive drive intended solely for the C128-users?

In many ways, it was a powerdrive, as it introduced the first use for 3.5″ disks for the C64 market.  These disks, together with the improved hardware, would allow for storage of 3160 blocks (or 800 KBytes) of data – compared to the capacity of the 1571 which had 340 KBytes, an increase by a factor of 2.4!
It could handle up to 296 files (instead of the 144 before) and introduced the notion of subdirectories onto the C64-userbase.  Fair enough, a subdirectory itself consumed up to 40 blocks and working with it back then wasn’t really easy.
And let’s not forget, it’s much harder to “break” a 3.5″ disk than the traditionally “floppy” of 5.25″ (remember the old “sticky fingers” problem).

Price-wise, it was OK, as it cost back then roughly €350,00, pretty much the same as a 1571 drive and you had much more storage capacity for the same price (true, a 3.5″ disk was a bit more expensive than the 5.25″), so all-in-all, it seemed a better deal.

But how did it score on the speed-front?  Was it faster?
Problems with incompatibility with the C64 ROM code, made it run unfortunately as slow as a 1541 drive although it did have the advantage of a larger RAM.  The 1571 drive had only 2 KBytes of RAM, making it impossible to load an entire 8 KByte track at once.  The 1581 had a whopping 8 KBytes of RAM, and this together with a utility called “Track Cache Buffer Loader” loaded all data first in RAM allowing then for RAM to RAM data transfer (which we’ve seen from last week’s review of the Silicon Disk, is lightning fast).
The speed gain was then roughly 10%.

The neat thing though, was that you could fit your 1581 drive and C64 with JiffyDOS chips (which also worked on the other drives), making it run a factor of 6-10 faster and hence bypassing the incompatability issues with the C64 ROM.

So in conclusion, the 1581 drive introduced the safer 3.5″ disks to the C64 owners and provided dramatic capacity gains in contrast to the other 15xx drives.  Fitted with JiffyDOS, this combined in a powerful peripheral that brought “mass-storage” capacity with fast disk I/O to the popular C64 market.

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3 Responses to Stange peripherals… The 1581 diskdrive

  1. Pingback: Stange peripherals… the HD20 hard disk | A Commodore Geek's Blog

  2. Pingback: Strange peripherals… JiffyDOS | A Commodore Geek's Blog

  3. Pingback: Utilities for the 1581 drive | A Commodore Geek's Blog

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