Strange peripherals… the HD20 hard disk

The weekend is about to begin, so this means it’s time for another “Strange Peripherals…” episode!

After all the different types of disks such as a RAM disk, the infamous 1581 disk drive and the Quick Data Drive, it’s time to take a look at something we usually only associate with PCs: a hard drive.

Back in 1991, a hard disk called the HD20 was released by Creative Micro Designs for the C64/C128 featuring a Conner CP-3020 SCSI disk.  Yes, that’s right, a real SCSI disk for your C64.  Actually, this isn’t so strange, as we know that in the Commodore world, all peripherals are really small computers themselves.  So a SCSI drive fits perfectly in this model.
The drive had an internal 6502A CPU, 64 KBytes of RAM and an EPROM containing the bootsystem for the drive.

The capacity was a whopping 20 MBytes, which could be extended up to 4 GBytes (remember, we’re still talking the early 90’s here!).
You could use this capacity in 4 different modes, such as a classic 1541, 1571 and 1581 mode, for which you could split up the 20 MBytes in 255 partitions, with each then having a “disk image”.
More fun though to use it in its native mode as a true hard disk, on which you could even create subdirectories and the likes (something which we mentioned in our article on the 1581, was also possible on the that drive, but on a hard disk, it really makes more sense).  Next to that, you could use real DOS-like commands to operate the drive.

Hooking it up to your C64 was easy, using the provided serial cable.  Ah, a serial cable I hear you say… isn’t this making the drive really slow?
Indeed, this was a major drawback which even made the drive only run roughly at the speed of a 1581.  Not really what you would expect from a hard drive.

There were 2 solutions to increase the speed though and really make good use of your drive.  The first one involved something we’ve seen in the article on the 1581 drive: JiffyDOS.
Upgrading your drive and your C64 to JiffyDOS set you back something like €60-€70 but the speed-gains were quite impressive, as can be seen from the comparison in the table below.

  C64/1541 C64/1581 C64/HD20 C64/HD20 (JiffyDOS)
202 Blocks (Load) 108 sec. 102 sec. 86 sec. 6 sec.
202 Blocks (Save) 188 sec. 71 sec. 73 sec. 25 sec.

The other alternative was to make use of your expansion port and a device called a “RAM Link”.  Basically, it would load the data in sort of a RAM cache before sending it to the C64.  This technique is comparable to the principle of the Silicon Disk (a RAM disk) that we discussed in a previous article.
By using this method, loading and saving 202 blocks takes less than 2 seconds!

Price-wise, the HD20 cost back in those days about €600, a good investment considering the fact that you had all the different drive modes and a real hard disk with DOS-like operating commands.

It sure is a peripheral that not many people know of, so definately one of the highlights in any collector’s collecion.

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4 Responses to Strange peripherals… the HD20 hard disk

  1. Pingback: Merging two worlds… with a disk drive | A Commodore Geek's Blog

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

  3. Pingback: Strange peripherals… the FD-4000 drive | A Commodore Geek's Blog

  4. Pingback: Hooking up an actual CD-ROM drive to the Commodore | MOS 6502

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