80-Bus News


Summer 1985, Volume 4, Issue 2

Page 20 of 31


by David Hunt

In this set of DRH ramblings he looks at a utility called LU, a deadly little program called VIRUS, the new Gemini GM870 80-BUS MODEM board and its software, the new UKM720 program, and Gemini’s latest BIOS, version 3.2.

DH disk storage crisis

Having sat down to write this sessions’ pile of disjointed bits, I’d done about a page’s worth and for some reason decided to save it.

ERROR Destination disk full

Well perhaps it’s not a crisis, I didn’t lose anything and I’ve plenty of secondhand disks knocking about, but I had a look at the full disk anyway, sure enough 784K with 4K free, and not a .BAK file in sight. Oh well, start a new disk; format it and label it. The label, –80BUS4 ??? Did that mean I’d completely filled three disks? It sure did! Almost 2.4M bytes worth, and that’s exclusively this mag and its predecessors, and then only what I’ve bothered to keep. Just as an exercise – a word count; I put everything into one big library using LU on the winnie, and then set SPELGARD the problem of counting the words whilst I went for a bite [Ed. – byte ?] to eat. Well of course, SPELGARD gave up at 65000 odd words, not surprising really, and I learned for the first time that SPELGARD has a 16 bit word counter. Well by now I really did want to know how many words had been written, so I truncated an average file to exactly 8K using a debugger and fed that to SPELGARD, then multiplied the result by 295. The result, I know you’re all dying to know – just over 300,000 words. Was it really that much? Well a re-count on another file came out about the same, so I guess it must be something like that. Just as well 80-BUS doesn’t pay me at a commercial word rate, I’d be quite rich and 80-BUS wouid be broke.

I mentioned LU; well this program has been lurking around the CP/M libraries for some while now, but I only came across it a few months ago. It’s marvelous for archive stuff, you know, the sort of thing you are loath to erase, but at the same time don’t ever intend to look at again whilst begrudging the disk space it takes up. In fact your typical DH 80-BUS article. No in fact DH type articles are too long and rambling to make much advantage of stuffing them into a library, the only advantage being in this case, keeping bits of things together. It’s much more useful at archiving lots of little things, letters, dBASE .CMD files and the like.

As you know, CP/M allocates space to files in blocks. In the good old days of single density 8"

disks with only about 240K of usable capacity, life was easy. CP/M builds a map of where things are put on the disk, it’s part of the directory entry for the file, and saved along with the name. That’s what file control blocks (FCBs) are all about, but then if you know about file contro! blocks, you know about directory allocation blocks. Anyway, the disk is carved up into nice small chunks, and allocated an 8 bit number. Now there can only be

256 discrete 8 bit numbers, so the maximum

number of blocks is 256. If the disk has a capacity of 240K, 240 1K blocks can be allocated. But like Topsy, disks growed, and double sided double density 35 track disk formats came along. These had a capacity of about 340K, and you can’t have 340 1K blocks, so the block size was doubled, 170 2K blocks. Then someone increased the number of tracks available by halving the track pitch, and 80 track disks appeared with a capacity of 788K. So now we have 197 4K blocks. Yes I know I’ve dodged the issue of single sided 80 track disks and the ‘double byte’ block allocation numbers used in winnies, but the fact remains that on the Gemini high capacity disks systems, we have 197 4K blocks.

The snag, you ask? Weil, it doesn’t matter if a program is two bytes long, it’s still allocated 4K of disk space, and so appears as a 4K file. More typically, letters and dBASE .CMD files are usually about 1K long, so 3K goes wasted. LU gets round this rather neatly. It constructs one file called a library file from a number of files, adding them end to end, and then puts an internal directory into the file. Yes, LU also has an internal biock size, but it’s only 128 bytes, so not much space is lost.

Of course LU must have snags, the biggest is that once a file is in the library you can’t execute it or even look at it, it has to be extracted from the library before you can do anything with it. Having said it’s for archive stuff anyway, this isn’t too much of a limitation. More annoying perhaps is it’s quirky syntax, which is also rather unhelpful and unforgiving.

Having said that you can’t do anything with a file in the library without extracting it, LU came with a couple of utilities, LDIR, so you quickly look at the file narnes in the internal directory, and LRUN so you can execute a xxx.COM file from within the library. Unfortunately if a program is executed from the library using LRUN, the program still can’t access any overlays it might want, they’re still buried in the library. The one utility that should have been there but wasn’t was LTYPE, as much of my library stuff is ASCII files. Still perhaps there wasn’t one or it had got lost or something. Or worse still, someone out there thinks DH should write one – no way!

I made a major mistake when I first got LU. I played with it a bit and thought it would come in useful

This is an OCR’d version of the scanned page and likely contains recognition errors.

Page 20 of 31