[Info-vax] Databases versus RMS

[Phillip Helbig---undress to reply]

In article <jmq9v4$krh$1 at Iltempo.Update.UU.SE>, Johnny Billquist
<bqt at softjar.se> writes: 

> > That's right. We had a similar device connected to PDP11 at the
> > newspaper I worked at that time. But these were not SSD's, they could
> > not store data without power present. They were RAM disks.
> 
> You cannot store data to a modern SSD today without power either...
> SSD - Solid State Device. Ie. no moving parts, no mechanics, just solid 
> state electronics.

Or Solid-State Disk.  There is a novella by Arthur C. Clarke which takes 
place in the far future where a character mentions the rule that no 
machine may contain any moving parts.

> But maybe you meant retain data without power. That might be. DEC was 
> fond of putting batteries on memories to make them keep their contents, 
> to get the same effect as for core memory.

Right.  This is why, in addition to HALT, there are both BOOT and 
RESTART options at the console.  These control what happens after a 
power cycle.  HALT stays at the console prompt, BOOT boots and RESTART 
tries to pick up where it left off, with the assumption that the 
contents of memory are still good (if this fails---as on all my VAXes 
since none of them have this battery-backed memory---for whatever 
reason, then a regular fresh BOOT follows).

> RAM disk is normally a term used for when you take some of your ram, and 
> implement a device driver to make it look like a disk to the OS.

Right.

> > And indeed there also was an SSB device with a RAM disk and a real disk
> > as backup. It had a battery to be able to write the data to disk in case
> > of a power failure.
> 
> Not sure what a SSB device is. But what you descibe sounds pretty much 
> like the cache every disk have nowadays.

SSB: Storage-Works Building Block, i.e. a hot-swappable "brick" which 
goes into a BA35X expansion box.  I have a couple of these: 256 MB and 
very expensive in their day.  Back when I was using a memory-starved 
machine I put page and swap files on these---slower than RAM (and 
cheaper) but faster (and more expensive) than regular disks.  Remember, 
as late as the mid-1990s DM 100 per MB was the going price for RAM.