Commodore 1581 Disk Drive
A true 3.5″ drive for the C64/C128, released in 1987, capable of high speeds which makes it a true gem for collectors as 3.5″ disks are still relatively easy to come by (in contrast to the almost extinct 5.25″ disks).
Like all Commodore disk drives, the 1581 is a “smart” device, as it has its own processor, memory, disk operating system.
The 1581 drive would allow for storage of 3160 blocks (or 800 KBytes) of data on the disks – 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.
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.
Problems with incompatibility with the C64 ROM code, made it run unfortunately as slow as a 1541 drive on the C64 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. 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.