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.