Floppy SSD Redux

Discuss construction, troubleshooting, and operation of the Altair 8800c computer

Floppy SSD Redux

Postby KenF » April 27th, 2022, 8:50 pm

There is an earlier discussion about an SSD for the Altair, so I offer my own solution. This one fits a smaller buss, but as I am about to begin the build of a new Altair Clone, I will remake it on an S-100 card.

It provides four (A,B,C,D) floppies that emulate the original standard - 128 byte sectors, 77 tracks with 26 sectors each. Actually, the driver could be altered to make about any size that is wanted, maybe a pair of 512k floppies, but I prefer it setup as the original CP/M standard. Of course, even on an 8085, they are far faster than physical drives.

My main machine has a pair of these cards, giving me drives A - H, although I have to say that the upper four are mainly used just for storing the odd utility.

The big chip is an Intel 8255 interface IC (love the device - use them everywhere) and the two static rams are 62512's, or equivalent. The other three are just two ordinary 74ls138's and a 74ls27 - a meg of memory that divided four ways gives a set of 256k pseudo floppies.

The 62512's come with an ultra-low power off drain, and with the 1mfd capacitor backed up by the coin battery, the data will be held for... a long time. I have one from several years back and it still had good data after a year on the shelf.

The driver is only about 256 bytes, so I just plugged it into the bios and forgot about it.

So, a floppy solution for about thirty bucks.
Attachments
ramdisksm.jpeg
Floppy Ramdisk
KenF
 
Posts: 30
Joined: April 25th, 2022, 11:13 am

Re: Floppy SSD Redux

Postby AltairClone » April 28th, 2022, 6:19 pm

Cool! Are you going to make the S-100 board appear as an Altair controller so that original Altair disk software will run?

Mike
AltairClone
Site Admin
 
Posts: 632
Joined: April 5th, 2013, 10:55 am

Re: Floppy SSD Redux

Postby KenF » April 28th, 2022, 7:24 pm

Hmmm... I stick to CP/M 2.2 pretty much and I have very little documentation (actually none) about the Altair disk subsystem. My group of hobbyists (long ago in the 70's and 80's) were mostly IBM employees and we had access to surplus drives. Thus, all of our disk efforts were toward supporting the IBM 33FD standard using the Western 1771 Floppy Disk Controller. In that way we were compatible with almost all of the add-on manufacturers - Morrow, Thinker Toys, Pertec and so on.

However, that being said, this FDC is nothing but a pile of static RAM accessed through 4 I/O ports. A driver could be written to emulate almost any disk subsystem I would think. In fact, I even sketched out a hard drive emulator using one of the 16meg static rams, but never got around to ordering the parts.

So I can't really answer the question without some information on Altair controllers.

Ken
KenF
 
Posts: 30
Joined: April 25th, 2022, 11:13 am


Return to Altair 8800c

Who is online

Users browsing this forum: No registered users and 7 guests

cron