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AXLON RAMDISK 320: A Review.........................Bill Morgan

AXLON's RAMDISK 320 is a system designed to add 320K of memory to an Apple, configured to look to the Apple like two very fast disk drives.  The speed improvement ranges from half the time for a large assembly to one-twelfth the time for directly dumping 192 pages of memory.


Hardware

The RAMDISK is a cabinet just the size of an Apple disk drive, containing the memory, its own power supply, and a backup battery.  There is also a large interface card, which includes 2K of static RAM for the operating system.

The backup battery is said to provide up to three hours of protection against power outage.  It did maintain power when we moved the system into another room (about 5 minutes), but you should certainly make floppy disk backups of the RAMDISK data before leaving the system unplugged overnight.  As long as it is plugged into the wall, the battery is kept charged and the memory is maintained.


Software

There are several programs supplied with the RAMDISK. These fall into the general categories of system software, utilities, and demonstrations.

RAMDSK1 is the operating system, which is stored in static RAM on the interface card, addressed in the $C800-CFFF space.  BRUNning this program hooks it into DOS and copies one or two mechanical drives into the RAMDISK.

RDCOPY copies between the mechanical and RAM disks, to load or back up the RAMDISK.  SELECT creates modified versions of RAMDSK1 for different slot/drive configurations.

The EXTRA40K utility allows you to access "tracks" 36-40 on the RAMDISK, but only on a level comparable to using RWTS directly.  That is, you must work in terms of addresses and track/sectors rather than variables and filenames.  The manual has a complete assembler source listing of this program.

SECTOR CHECKER and BYTE-BY-BYTE are self-test utilities to verify correct operation of the RAMDISK.

The demonstrations are The Directory and the Mini-Base Phone Book. The Directory is a large, disk-based, data-base program, in machine language, which uses the speed of the RAMDISK to its full advantage.  The problem with this program is that it is strictly fixed-format, with no provision for modifying the record structure.  The fields built into a record are last name, first name, dept #, mail stop, phone, special interest 1, special interest 2, and comments.  If you are a large company needing an on-line, internal phone directory, then The Directory is outstanding.  Otherwise, it's just an interesting demonstration of the system's capabilities.

The Mini-Base Phone Book is a memory-based data base, somewhat similar to File Cabinet.  The Mini-Base is also set up as an internal phone directory, but since it is written in Applesoft, it can be modified to suit your needs.  The documentation includes instructions for changing the record structure.  The manual also contains instructions for calling special machine-language routines for keyboard input, fast loading of text files (in a specified format), and fast sorting of a string array.


Documentation

The manual is in three sections:  63 pages on the system, 34 pages on The Directory program, and 43 pages on the Mini-Base Phone Book program.  It all comes in a large (8 1/2 by 11) 3-ring binder.  The system section has chapters on setting up the RAMDISK, using the included software, calling it from DOS 3.3, attaching and using it in Pascal, technical information, and accessing the system from assembly language.

The setup and software chapters are quite good; the DOS chapter just says that everything is standard. I don't have Pascal, so I can't evaluate that section.  The technical and assembly language chapters have all the information about memory usage, addressing, and programming techniques needed to use the RAMDISK without all of DOS's overhead.


Using the RAMDISK

To use the RAMDISK with your programs, you need to copy the RAMDSK1 program onto your disk and set up the HELLO program to BRUN RAMDSK1.  This will load the operating system into the interface card, then fast-copy your disk into drive one of the RAMDISK.  Once your information is loaded into the RAMDISK, you can use all the normal DOS techniques to read and write files; the only difference is speed.

You can avoid the DOS overhead either by calling RWTS in the usual manner, or by directly using the RAMDISK registers and memory window.  To do that, you just store track, sector, and drive information into two bytes, then read the data from $C800-C8FF.  This approach is fastest, but you must then take on all memory management chores.  Appendices to the manual list assembler source code for routines using both techniques.


The Negative Side

We discovered one apparent bug in the RAMDISK's operating system.  The program does not properly update the slot and drive found parameters in the I/O Control Block used by RWTS.  If a program tries to use those locations to determine which drive it was run from, it will get the wrong data.

Mechanical disk drives are known to be error-prone, so DOS has some built-in protection against errors.  Each sector is recorded with a checksum; when a sector is read the checksum should match.  This is very poor protection, but it does catch most errors.  The RAMDISK has no such protection.  The RAMDISK is much less likely to have any errors than the mechanical drives,  yet it still would be nice to have at least a sector checksum.  Parity on each byte would be even better, but it would be expensive.  


Timing Comparisons

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     Operation         Disk II time      RAMDISK time

Assemble 102 sectors      89 sec.           41 sec.
   of source code.
BLOAD Hi-res screen.      11 sec.            3 sec.
LOAD Applesoft program.   14 sec.            4 sec.
Dump RAM (192 sectors)     9 sec.           .8 sec.
   calling RWTS.
Dump 192 sectors direct     n/a             .7 sec.
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Summary

The RAMDISK is a well-made and well-documented unit; it performs as advertised.  The RAMDISK gives a terrific speed improvement over mechanical disk drives, especially if you do your own reading and writing and avoid DOS.

Two standard Apple drives with controller at normal retail prices would cost $1180; RAMDISK goes for $1395, and you get the equivalent of 10 extra tracks thrown in.  (On the other hand, several non-Apple drives are available with 40 to 80 tracks, at competitive prices.  And the 5- and 10-megabyte Winchesters are rapidly falling in price.)
  I have seen RAMDISK advertised for as low as $1170 in Byte Magazine.

The RAMDISK 320 is available from AXLON, Inc., 170 N. Wolfe Rd., Sunnyvale, CA 94086, (408) 730-0216.  RAMDISK 320, The Directory, and Mini-Base Phone Book are trademarks of AXLON INC.
