adrian@eagle.UUCP (A.Freed) (04/25/85)
We are hearing of hacks to provide 1Mbyte of memory for the Mac. One of the best ways of using this memory is to have 512k for programs and a 512k ram disk. Doesn't this mean that there is a niche for an external ram disk? This would suit better those of us who don't want non-Apple approved hardware intrusions. I would much rather pay for a ram-disk than a second floppy drive. You could boot off the ram-disk (by setting it up from the floppy and hitting reset). Battery backup ought to be straightforward. 30secs is enough to transfer the ramdisk to a couple of floppies. Two questions: Is anyone doing such a thing? What performance limitations does the hardware interface have to the second drive? I am assuming that 0 seek time provides the most benefit.
db@cbosgd.UUCP (Dave Bursik) (04/26/85)
I agree that an external ram disk would be a good idea. To make it more viable, however, I'd like to see it have multiple modes of operation: 1) As an external disk replacement (per the original posting) 2) As a "whole disk cache" (if that's not a contradiction in terms) that could sit in-between the external disk an the main unit. The advantage (real or imagined) of the second arrangement would be that the ram disk could simply swallow-whole a disk that is inserted in the external drive, without user intervention. Given a larger memory, it might be able to first swallow a disk from the external drive (as a ram disk) and then act as a cache for a different disk (inserted in the external drive once the first one has been ingested). Comments, anyone? Dave Bursik/..cbosgd!db
gus@Shasta.ARPA (04/27/85)
> I agree that an external ram disk would be a good idea....
I don't. The whole idea of a RAMdisk is that it is just that...
RAM. An external ramdisk would still have to go through the external
serial ports, and thus not be any faster than the AppleTalk fileserver.
(I don't think anyone will create a product like this that would not be
compatible with AppleTalk.)
Keep dreamingvishniac@wanginst.UUCP (Ephraim Vishniac) (04/29/85)
In a similar vein (novel sorts of RamDisks), how about a "smart" ramdisk that does data compression/decompression on the fly? I'd take odds that the actual information content of an apparently full 400k floppy could be expressed in less memory at some cost in coding/decoding. Packbits might be the fastest and easiest way to go (although not necessarily the most space-efficient). Now your puny 316k ramdisk can contend with your beefy 400k floppies! :-) Some problems: What's the size of such a ramdisk? Depends on what's in it. How do you decide what's safe to copy in? Should you overcommit? Undercommit? What if the disk is full and someone re-writes a sector with less compressible data? I see some possibilities for dealing with these problems. If you're low on space (more than x% of real memory full), you could snarf a little from the heap and declare yourself full, for example. But, your ramdisk support code might become large enough to negate any net advantage. -- Ephraim Vishniac [apollo, bbncca, cadmus, decvax, harvard, linus, masscomp]!wanginst!vishniac vishniac%Wang-Inst@Csnet-Relay
dennisg@sdcrdcf.UUCP (Dennis E. Griesser) (04/30/85)
In article <4967@Shasta.ARPA> gus@Shasta.ARPA writes: >> I agree that an external ram disk would be a good idea.... >I don't. The whole idea of a RAMdisk is that it is just that... >RAM. An external ramdisk would still have to go through the external >serial ports, and thus not be any faster than the AppleTalk fileserver. >(I don't think anyone will create a product like this that would not be >compatible with AppleTalk.) Actually, external RAM-disks have been around for quite awhile. I remember seeing an ad about five years ago for one that had an interesting twist. It had a diskette-style interface. This made it hardware and software compatible with any machine that could talk to a standard drive, while preserving most of the speed benefits. I think that a RAM-disk that connects like a diskette is a clever idea, but impractical for a number of reasons.
gus@Shasta.ARPA (04/30/85)
> In a similar vein (novel sorts of RamDisks), how about a "smart" > ramdisk that does data compression/decompression on the fly? I'd > take odds that the actual information content of an apparently full > 400k floppy could be expressed in less memory at some cost in > coding/decoding. Packbits might be the fastest and easiest way to > go (although not necessarily the most space-efficient). Now your > puny 316k ramdisk can contend with your beefy 400k floppies! :-) Data compression kills performance. Try out something like compace/ uncompact/ccat on UNIX and you will see what I mean. Packbits is nice for repetative data such as MacPaint pictures, but not for less regular data such as 68K code. (what you will normally put on your RAMdisk.) Face it, folks, RAM disks are supposed to be FAST. Any optimizations would slow them down to floppy speeds making them useless for what they were intended. I think you guys are all on the wrong track. Sure, you could figure out some neat new external Ramdisk, internal kludge, etc. but this will not give an order of magnitude better performance. The next step is to shell out real $$$ for new hardware such as a hard drive. There is one exception - a disk cache. This will cache blocks read into memory from disk so that they don't have to be read-in again. For example the first time you load the finder, it loads at floppy speeds. The second time, it comes in at RAMdisk speeds. This has certain advantages and disadventages to a RAMdisk which is pre-loaded at boot time. It is safe to say that a disk cache (such as the turbobuffer) is in the same realm as a ramdisk as far as functionality is concerned. Gus Fernandez
ehl@Navajo.ARPA (05/01/85)
Having used a disk cache (the TurboBuffer) for a while, I agree with Gus' assessment. My feeling is a bit stronger, though -- for most applications, I find a disk cache SUPERIOR to a RamDisk -- it's more useful for multiple programs since you don't have to store the entire system file. In particular, it's a godsend when I use Mac C -- I don't have to go into contortions trying to get the development programs to work with the RamDisk, and compilation whizzes right along. -- Elgin Lee UUCP: ..decvax!decwrl!glacier!navajo!ehl ARPA: ehl@su-navajo.ARPA, ehl@su-score.ARPA
tsc2597@acf4.UUCP (Sam Chin) (05/03/85)
<>
The last time I looked in PC Week the prices of 256K Ram Chips were down to
about $175 a megabyte (36 256K chips at <$4.99 a piece). With all the new
LSI ram controller chips, I bet you could put about 5Mb on a Ram Drive for
under $1000 by the years end. For the price of a hyperdrive, you could
probably get a 20Mb ram disk. People who deal with high performance
architechtures seem to be of the opinion that disk cache should be 10X main
memory. You can use the cheapest possible ram for ram disk - 300-400 ns
stuff and still get amazing performance. With ram disks of these sizes,
backup power is totally necessary but the UPS I've seen run under $400.
Sam Chin
allegra!cmcl2!acf4!tsc259
tsc2597.acf4@nyu.ARPAjoel@peora.UUCP (Joel Upchurch) (05/06/85)
> There is one exception - a disk cache. This will cache blocks read into > memory from disk so that they don't have to be read-in again. For example > the first time you load the finder, it loads at floppy speeds. The second > time, it comes in at RAMdisk speeds. This has certain advantages and > disadventages to a RAMdisk which is pre-loaded at boot time. It is safe > to say that a disk cache (such as the turbobuffer) is in the same > realm as a ramdisk as far as functionality is concerned. > > Gus Fernandez If you look at page 472 of the May Byte you will see an announcement for a disk cache for the Macintosh called TurboCharger. It appears to be only intended for Fat Macs and costs $95.
ems@amdahl.UUCP (ems) (05/09/85)
> <> > > The last time I looked in PC Week the prices of 256K Ram Chips were down to > about $175 a megabyte (36 256K chips at <$4.99 a piece). With all the new > LSI ram controller chips, I bet you could put about 5Mb on a Ram Drive for > under $1000 by the years end. For the price of a hyperdrive, you could > probably get a 20Mb ram disk. The interesting thing in all of these discussions has been how they emphasize the technical side. This would/wouldn't work because {it won't, no one would want it, hard disk would be better, real ram disk doesn't go slow, etc}. Here at last we have a posting that gets to the real question. Would someone buy one. The prices given look good. As a more or less average Mac user (technically proficient, but not a True Hacker) I should be representative of a reasonable sized chunk of the market. I would buy one. Why? I want a Fat Mac with fast disks. I have a Fat Mac that spends all his time looking like a skinny mac because he uses a RAM disk all day. An External RamDisk would be fast and would not impact my Fat Mac. For mass storage, I would continue to use my floppys. If the ERamDisk could do the compression on the fly (NOT impacting the Mac processor) so much the better. Why do I want one? To reduce the number of times I have to wait while the disk turns. It would do that. Where do I pay? -- E. Michael Smith ...!{hplabs,ihnp4,amd,nsc}!amdahl!ems Tilapia Zilli is the way and the light. This is the obligatory disclaimer of everything.