CW%APG.PH.UCL.AC.UK@CUNYVM.CUNY.EDU (06/21/91)
I'll volunteer to review the bank switching RAM cards.
Who wants to send me one for appraisal? :-)
Conradakcs.joehorn@hpcvbbs.UUCP (Joseph K. Horn) (06/22/91)
Tim Conrow writes: > So, has anyone out there built up any experience with the new higher > density cards, particularly the 256k card? Does the 256k version > require bank switching? Is bank switching a pain, or mostly ok? > It's time for a review. Is anyone game? Both the 256K and 512K cards require bank switching, because the 48SX can only talk to 128K per port. The only difference between the 256K and 512K cards is that the number of banks (128K each). But bank switching is NOT a pain. TDS did it right. It's not a hardware switch. It's totally done by programmable commands. There is a single write-protect switch, like all RAM cards have; it write protects only the currently active bank. (The other banks don't even exist, as far as the 48 is concerned, so they're REALLY write protected! I suppose a static crash could scramble them, though.) There are two kinds of bank switching commands, a safe one, and a dangerous one. The safe one performs a "system halt" (like you get by pressing ON-C) after bank switching, so that there are no "loose ends" in memory, such as addresses of objects that were in the old bank but of course are no longer in the new bank (or at least not at the same address). Unfortunately, this command cannot be used within programs, because programs cannot continue after a system halt. This command is used from the keyboard, and can be thought of as equivalent to unplugging one 128K card and plugging in another, with ALL that this implies about access to the information in each card (bank). The dangerous bank switching command merely performs the switch. No system halt is performed. This means that careless use can result in a Memory Clear. But the careful programmer can use it, so that a program can effectively be 540K long (in chunks), or have 512K of "RAM Disk" available for data. (A megabyte with two cards!) Note well that the 256K and 512K RAM cards cannot be used effectively as MERGEd memory. Since the 48 requires you to FREE a card before removing it, the TDS cards must likewise be FREEd before being bankswitched. If MERGEd, you can't bankswitch, which sorta defeats the whole purpose of these cards. But if you merely need a temporary extra 128K of main memory, you _can_ MERGE the current bank, and then FREE it afterwards. What most people will probably do is use one 128K card and keep it MERGEd, and one 512K card and keep it FREEd. This allows 160K main memory, and 512K ram disk; an optimum configuration (for now). These are solely my observations and opinions. Tripod Data Systems, EduCALC, and Hewlett Packard do not pay me; it's vice versa. -- Joseph K. Horn -- Peripheral Vision, Ltd. -- P.S. Conrad says he'd like a free TDS card for reviewal. Heck, I'd even like one at list price. EduCALC is having trouble getting them at all. Maybe some day I'll own one and stop playing with the demo at EduCALC. -jkh-