Percom Doubler II
LN Doubler 5/8
NEWDOS80 Version 2.0
Percom TFD 100-1
Double density disk storage - a close look at all you will ever need to upgrade your Model I.
Model I users have always been plagued by a problem called data sepa-ration, when the disk controller has trouble separating data from other bit streams of information, such as the clock cycle. This problem can become severe particularly when you are for-matting or writing to the innermost tracks of a disk. With double density (since the current double-density disk controllers all use a built-in data sepa-rator), disk I/0 is actually more reli-able than single density. My old drives reported fewer disk read/write errors from single-density I/0 with the Radio Shack disk controller when I moved up to double density, You can store more information on a double-density disk as well - 184,000 bytes on a formatted disk. With a four-drive system, single-density users are limited to a meager 332,000 bytes of on-line storage, whereas double-density users can have up to 700,000 bytes on-line.
How do you get double density? Which disk controller and DOS should you choose? There are a wide variety. I contacted many manufacturers of dou-ble-density products, and those that re-sponded are represented here.
Two double-density disk controllers, five DOSes, and four disk drives are re-
viewed. Although most of this infor-mation is applicable to Model I users only, four of the DOSes have Model III versions. Indispensable in my testing of the disk dr.ives and disk controllers was the Floppy Doctor, a product of the Micro Clinic in Fountain Valley, CA. The util-ity comes on a self-booting disk and has a memory test and nine disk-drive tests.
The Disk Controller
The disk controller is the circuit in the expansion interface that lets the computer talk to the disk drive. The Western Digital disk controller that ac-companies the Radio Shack Expansion Interface is a single-density disk con-troller, but it can write several kinds of DAMs (data address marks). To allow compatibility, both the Percom and LNW disk controllers allow your com-puter to use the original disk controller as well as the double-density disk con-troller.
You install both in the same manner. First, dismantle the Expansion Inter-face and remove the disk-controller chip from its socket. Next, plug the old disk controller onto your new disk-controller circuit board (which houses an additional, double-density disk con-troller) and plug the new circuit board into the disk-controller slot. It will take about 5-15 minutes to install, depend-ing on your familiarity with the parts involved. It requires no soldering, trace cutting, or any modification to existing circuits.
I reviewed the Percom Doubler II and the LN Doubler 5/8. The Percom Doubler comes with easy-to-follow in-
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structions and Percom's own DBLDOS; essentially a TRSDOS patched to run double density with a few corrected flaws. It sells for $169.
The LN Doubler 5/8 comes with better instructions and an even easier installation manual. The manual in-cludes the Western Digital technical manual for their disk controllers. The LN Doubler 5/8 also supports eight-inch floppy drives (if you have the nec-essary speedup enhancement to your Model I), and comes with DOSPLUS, a much better disk operating system. The LN Doubler 5/8 sells for $220,
Are they different in performance? No. I was unable to demonstrate a significant difference in any disk-con-troller functions between the Percom Doubler II and the LN Doubler 5/8. Reliability testing showed no signifi-cant differences in granules locked out or in read/write errors. This was using the brand new drives I received for this review and older Pertec drives. New Maxell disks were used and were for-matted to 40 tracks using double density.
A disk operating system is a pro-gram that controls computer operation in a disk-based computer system. The aspects of a DOS that I consider im-portant are: ease of use; speed of oper-ation; accompanying utilities, such as editor/assemblers, file utilities, debug-gers, monitors, and languages; read-ability and completeness of documen-tation; compatibility with other disk formats; and cost.
The DOSes reviewed here all sup-port double density and are avail-able for the Model III. They are MULTIDOS, NEWDOS80 2.0, DOSPLUS, and LDOS.
MULTIDOS, written by Vernon Hester, is the most inexpensive of these DOSes and has many features its more expensive competitors don't have. It is the only totally compatible DOS around. It will read any of the other disk formats, including DBLDOS (none of the others will). It is also a "no-hang" DOS, meanin'g that even if you remove the operating system from drive 0 and the DOS tries to access the system utilities on the DOS disk, it won't up and quit, as will the other DOSes. It won't do what you wanted, but it will remain in control of your computer. One useful, although per-haps minor, convenience is that press-ing the enter key without input will re-
execute the last DOS command. MULTIDOS is a fast DOS as well.
The only major problem with MULTIDOS is that it only checks four times on a read/write. My old Pertecs show many more "Data Record Not Found" errors with MULTIDOS than the other DOSes, which check 10 times before returning an error.
The manual is a terse 66 pages (not including a few pages of errata and ad-ditional information). It lacks an in-dex, but covers the features of MULTIDOS adequately, provided that you already have the TRSDOS manual. This complaint is true of NEWDOS80 as well. DOSPLUS and LDOS have manuals that don't require that you have read the TRSDOS man-ual to understand them.
MULTIDOS has many useful li-brary commands besides those provid-ed in TRSDOS. You can disable the break key from DOS, and build and execute DO files (although you cannot run a Basic program and pass input to the Basic program from the DO file). Some of MULTIDOS's commands in-clude: Forms, which lets you specify lines per page and line length for print-ed output; Hash, which returns the hash code of a file ID; and KEYBRD, which sets the keyboard parameters. MULTIDOS has a default keyboard driver that provides a repeating, flash-ing block cursor, but this can be changed with the KEYBRD command. Link and Route control the I/0 of data to the video and printer. You can send everything that goes to the printer to the video too (or instead) and vice ver-sa. Topmcm allows you to set the top-of-memory pointer from DOS.
MULTIDOS has a number of useful system utilities. Backup lets you make speedy backups on a single drive and alter the number of tracks on it at the same time. Copy allows single-drive copying of single files, including to and from non-MULTIDOS disk formats. Format formats disks in single, dou-ble, or P (DBLDOS) density formats.
Other utilities include a disk-based version of Radio Shack's Editor/As-sembler, a RAM Scanner to locate a one or two-byte word in memory, a graphics utility to allow direct key-board entry of graphics characters, a printer spooler, and best of all, MULTIDOS's Versatile File Util-ity (VFU). VFU is a utility for frequently need-ed disk operations, including purging files, printing a disk directory, multi-plying file copies, and executing menu-
based programs. The Purge option gives a screen of the available files, as do the Copy and Execute commands.
MULTIDOS has the best Basic around, SuperBasic. It also has a pro-gramming and debugging Basic called BBasic with Boss built into it. Super-Basic is the smallest Basic available since it uses extensive overlays for vari-ous operations - SuperBasic leaves 40,000 bytes free after loading. Basic can be loaded directly, recovered (with BASIC*), and it provides two more options: BASIC! loads Basic and re-covers a program left there by a non-MULTIDOS Basic. This means you can recover a Basic program left from running DOSPLUS or NEWDOS80 and recover it by inserting a MULTI-DOS disk in drive 0, pressing the reset key, and typing BASIC!. BASIC# re-covers a Level II program in memory. The recover utilities allow direct con-tinuation of a program. SuperBasic provides a special form of Level II to provide even more memory when needed.
BBasic incorporates Boss into Basic, and allows single stepping of Basic programs, reviewing the current values of any set of variables at any time, breakpoints, and an improved trace function. Other than this, BBasic is just like SuperBasic, except it takes up more room.
SuperBasic allows you to use single-key abbreviations for some com-mands. It alsa has a Pn command to display a requested page of a program. Several additions to Basic are provided with CMD"xxx" commands. CMD "C" compresses your program with-out eliminating remark statemeplts. CMD"E" displays an error message associated with the last disk error. CMD"K" zeros all elements of an Ar-ray. CMD "L" deletes an arrag-. CMD"M" moves a program line. CMD"N" duplicates a program line. CMD"0" opens an additional file buffer. CMD"Q" performs a string sort of a single or double-dimension string array, and CMD"V" displays all current scalar variables and their values.
SuperBasic has overlay utilities to re-number parts of your Basic program, search for ASCII strings within pro-gram text, change all or part of vari-able names, change graphics codes (CHR$(X)") into packed strings and it provides a cross-reference utility that shows all line numbers that contain specified variables. SuperBasic uses Name to chain programs without los-ing variables. I think SuperBasic is the
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best Basic to accompany any DOS available.
NEWDOS80 2.0 is a double-density DOS that writes and reads a specific disk format differently from the other .DOSes. The familiar gran for granule has been replaced by lumps. What's a lump? NEWDOS80's documentation doesn't go out of its way to tell you. It is definable with the PDRIVE GPL pa- rameter, so that there are between two and eight granules per lump. You can define the granules-per-lump (GPL) parameter as eight. Once you do so, the DOS's features are about the same : as in the others.
NEWDOS80 2.0 will read other : formats, but they must be configured with the PDRIVE (similar to , MULTIDOS's CONFIG) each time a different disk is used, particularly if the disks are in different densities. To ' get around this problem, The Alter- nate Source sells a program that gives NEWDOS80 2.0 automatic density recognition. This program is called DDSD and costs $19.95.
One of the examples in the PDRIVE section implied that I could read the directory of a Model III disk. I was unable to read the Model III disk's directory with NEWDOS80 : 2.0. You can, however, copy from a . Model III TRSDOS disk on a Model I with this DOS.
It will take you longer to get started with NEWDOS80 than with the other operating systems presented here. This .; is partially due to the manual's techni- cal approach, and partially to the ap- proach taken by the DOS in its perfor- mance of the various functions. All the other DOSes allow you to back up a disk with the familiar Backup com- mand, but NEWDOS80 requires using the Copy format. Once learned, NEWDOS80's approach is quite use- able and powerful.
NEWDOS80 has a large number , of library commands. The most not- able are:
NEWDOS80 also sports a miniDOS not found in the other DOSes. The miniDOS allows the execution of DOS library commands except Append, Chain, Copy, or Format. Since it is in-terrupt driven, it can be used from al-most. any program that keeps inter-rupts active and uses the NEWDOS80 keyboard driver.
The utilities provided by NEW-DOS80 include the ever-popular Superzap. It also supplies a patched version of Radio Shack's Editor/As-sembler and a disassembler. The disassembler writes disassembled code to disk from where it is loaded by the patched assembler. It will also send the disassembly to the printer or screen and display a cross-reference table.
LMOffset is a program used primar-ily for loading system tapes that over-lay the DOS and store them on disk, Chainbld is used for the creation and editing of Chain or DO files. ASpool is a printer spooler.
NEWDOS80 also sports an en-hanced Basic. Enhancements include toggling the break key, abbreviated line listing and editing commands similar to MULTIDOS's SuperBasic. Chaining is allowed and the Merge coinmand merges non-ASCII files. REF displays a reference list af variables and line numbers, and can specify different outputs in a number of ways.
CMD "F = ERASE" and CMD"F = KEEP" allow selective clearing of Basic variables, like the MULTIDOS SuperBasic CMD"L", only more powerful. The first format selectively clears a number of variables in a sin-gle statement, while the second for-mat clears all except the declared vari-ables. Some other CMD enhance-ments include clearing all Returns and For... Next loops from the stack, dynamic deletion of text lines, swapping of variable contents, single-stepping Basic, recovering a deleted program (providing it hasn't been overwritten in memory), and sorting arrays. CMD"0" sorts a multidi-mensioned array.
NEWDOS80 has some extensive disk I/0 enhancements to Basic as well. The manual spends 20 pages dis-cussing these disk I/0 enhancements in chapter 8 alone; appendices A and B
feature 65 more pages on the topic.
NEWDOS80 handles the standard sequential (which they call print/input) and random (which they call field item). It also handles marked item (which has three subtypes) and fixed item (which has two subtypes). Ran-dom-access files can be of 1-256 bytes in fixed length. The fixed time and marked item files have a maximum rec-ord length of 4,095 bytes.
Sequential files can only be accessed sequentially. That is, if you want to read item number 200, you must wade through the first 199 items. Random-access files can access record number 200 directly and are more useful and powerful.
In fixed and marked item files, Get and Put are used to access data in the I/0 buffers. The type and length of each item is determined by the IGEL (item group expression list) of the Get and Put for fixed-item files, but in marked-item files, the item always be-gins with marker bytes, specifying the format of the item. Although they are initially hard to understand, these new file types are quite useful.
NEWDOS80 is a good DOS. The Basic is not as good as MULTIDOS's, but it operates well. It has a disassem-bler, Superzap, and other powerful utilities. Apparat supplies zaps free to registered owners and has provided good customer support in the past. Un-fortunately, it does not have automatic density recognition.
DOSPLUS comes with the LN Dou- ' bier 5/8. It has automatic density rec-ognition, although it cannot read DBLDOS format.
The approach to operating system functions took a departure from TRSDOS with DOSPLUS. The DIR command automatically displays the information normally supplied with DIR (A) in TRSDOS, and a new com-mand, CAT, displays the abbreviated directory normally retrieved with DIR in TRSDOS. It would be nice if the DIR command displayed the number of granules left.
DOSPLUS has an automatic repeat-ing, lowercase keyboard driver and DO-file capability. The Format com-mand works quickly and verifies the tracks backwards rather than forwards to save time (since the drive head is al-ready at the highest track, it needn't move back to track 0). DOSPLUS Model I and III double-density ver-sions are directly compatible, meaning that a Model I DOSPLUS disk can be
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read by a Model III DOSPLUS. This does not mean that a Model I DOSPLUS can read a Model III TRSDOS disk. DOSPLUS does come with a Convert command to transfer files from a Model III disk to a DOSPLUS disk, somewhat like NEWDOS80.
Although DOSPLUS does not have a VFU command similar to MULTIDOS, Picotrin Technology of Lantana, FL markets a DOSPLUS-compatible program that provides cur-sor-oriented functions.
The DOSPLUS manual is reason-ably well done except for the omission of an index. The technical section is particularly good in how it describes the entry and exit points for the various DOS routines and DCB (device control blocks).
The library functions are similar to the DOSes previously described. The DO construct works well and lets you specify in the command the reserved high memory for the DO file.
The DOSPLUS utilities include a printer spooler, single-drive copy, Crunch (a program that compresses Basic programs saved on disk), Disk-dump and Diskzap (floppy-disk edi-tors similar to Superzap), Map (shows file locations on a disk), Restore (recovers killed files), Sysgen (creates nonstandard system disks), Tape (similar to NEWDOS80's LMOffset), and Transfer (for multiple file copies from one disk to another).
DOSPLUS enters Basic differently than MULTIDOS or NEWDOS80. The Basic is enhanced as well. TRON allows: you to single-step Basic, and Tab tabs on a line printer beyond 64 columns. You can move and copy Ba-sic program lines, and DOSPLUS Ba-sic has a large number of abbreviates.
DOSPLUS also comes with a tiny Basic called TBasic. TBasic occupies slightly more space than MUL-TIDOS's SuperBasic, but has no file space allocated. TBasic lacks many of the enhancements found in regular DOSPLUS Basic, but is useful because it will still run the full set of Basic com-mands. TBasic displays abbreviated er-ror messages in a further attempt to free up memory.
LDOS recently reduced its price from $169 to $129, due to the large vol-ume of sales. Registered LDOS users receive a quarterly magazine called, appropriately enough, The LDOS Quarterly, support hard to match. LDOS comes with a rather imposing
300-plus-page, well-written manual. The LDOS manual is the best of the DOSes reviewed here.
In order to make LDOS run with double density, you must use the PDUBL disk-driver program, which sits at the top of memory. This creates some real hassles with programs in high memory at times. You can use the Sysgen command to save the driver configuration so it automatically loads on boot. Model I users cannot boot up on a double-density LDOS disk - it must be single density, although you may change it to double density after the boot, a minor inconvenience.
LDOS on the Model I will not read a Model III TRSDOS disk, although the library command CONV can be used to transfer files from a Model III TRSDOS disk.
The library commands in LDOS are similar to those available in the other DOSes. Trace supports and displays the PC register in the upper right cor-ner of the display, and Filter is similar to the Route command on other DOSes but better. It establishes a pro-gram to filter the I/0 path of some de-vice. Several filter programs are sup-plied with the LDOS disk.
MINIDOS/FLT is a filter similar to NEWDOS80's miniDOS. In it, you can toggle the clock on and off, enter Debug, display free space, kill files, and so on. A filter for the line printer is also provided.
One of the most powerful features of the LDOS operating system is its job control language (JCL). A DO or Chain option is available for all the other DOSes, but a true JCL is lacking. The LDOS JCL is actually a compiled language. It can handle conditional statements and support variables. LDOS allows concatenation of vari-ables (which they refer to as tokens) and logic expressions using NOT, AND, and OR. LDOS JCL allows macros in its programs. This means that you can specify a macro name and some complex function will be per-formed.
The JCL feature is a powerful one, although it could be made more power-ful by adding the ability to direct exe-cution of the JCL program on the basis of the results of some program. An in-teractive control language (ICL) is available for NEWDOS80 version I and it allows this flexibility.
One of the utilities includes CMDFILE. Similar to NEWDOS80's LMOffset but more powerful, this
code programs together, saving them to disk or tape, moving them around in memory, and so on. CONV moves files from a Model III TRSDOS disk to an LDOS disk. Since this program can be used by a Model I running double den-sity, this provides the only utility to move programs from a Model III disk to a Model I disk. LCOMM is a com-munications program that allows your TRS-80 to talk to other TRS-80 com-puters or to bulletin board systems, such as Forum 80. Repair updates and corrects information on certain types of disks to make them useable to LDOS. This utility is more useful for Model III users than for Model I folks.
LDOS's enhanced Basic, LBasic, has some abbreviations and allows sin-gle-stepping of Basic programs. Re-store has been updated to allow you to specify a line number to start the Re-store at. LBasic allows chaining of Ba-sic programs without loss of variables. LBasic can also sort arrays and provide reference information on Basic pro-grams. LBasic is good, but in my opin-ion, not as good as the Basics in the other operating systems.
LDOS is a good DOS, but there are a few minor inconveniences. The Basic could be more powerful, and it would be helpful if the top of memory was free. (PDUBL sits at the top of memo-ry if you're using double density.) The manual is quite good, and the Filter and JCL features make this the most powerful microcomputer DOS around. Finally, the LDOS support is unprecedented in quality and ease for the registered user.
As you can see, all these DOSes have their good points. MULTIDOS has its low price tag, versatile file utility, no-hang ability, virtually total compatibil-ity, and the excellent SuperBasic. The manual is a bit terse and MULTIDOS only checks a read/write four times.
NEWDOS80 has good utility pro-grams like LMOffset, a disassembler, and Superzap. The manual, however, is lacking a tutorial and NEWDOS80 needs automatic density recognition. DOSPLUS has Diskdump, Diskzap and automatic density recognition. LDOS has its excellent manual, great customer support, very flexible filter-ing of I/0, and a powerful JCL. Which you choose depends very much on your applications.
A disk drive must be able to move a read/write head very precisely to any
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location and rotate the disk within pre-cise limits so that address marks and data can be accurately located. The drive speed is supposed to be 300 rpm. Most drive manufacturers say that a one-percent variation in-drive speed is tolerable, and often a precisely adjust-ed drive will still vary within + one per-cent of 300 rpm.
Older minifloppy disk drives had 35 tracks and wrote only in single ,density. Technology has improved, and now 80 and even 96-track minifloppy drives are available in single or in double density.
I was hoping to find differences in reliability of the brand new drives un-der severe stress-testing conditions. As long as I kept below the upper limit of the speed of the stepping motor of the drive, I was unable, generally, to get any errors in these drives. I could find no clear-cut reliability differences among the various drives, so it was im-possible to statistically investigate the presence or absence of an interaction of effects due to the disk controller used. I did, however, discover dif-ferences in their operation. The drives I reviewed are: Percom model TFD 100-1, PMC model SFD-51-A, Teac, and Trak model 5410-121.
The Percom is the only one of these drives that is flippy, meaning that you can remove the disk from the drive, flip it over, and reinsert it into the drive and write to the other side of the disk. This effectively doubles the amount of storage you have in your disk library. The Percom drive also has the drive-cable card extending out from the rear of the machine, so it is easily accessible without removing the case, a nice fea-ture. It has a stepping-motor speed that allows you to seek tracks at 12 millisec-onds. This is faster than the Teac (at 30 ms) and my Pertecs (at 20 ms), but slower than the PMC and the Trak (both at 5 ms). The list price of the Per-com drive is $305.
The PMC drive also has the drive-cable card extending out the rear of the drive. It has a fast-stepping motor with 5-ms track seeking. It allows writing only to one side of the disk.
The Teac drive was the slowest of the bunch, requiring a minimum of 30 ms to seek a track. In order to change the drive cable, you must remove the cover. The card for the drive is incon-veniently spaced, meaning the drives must be slightly closer than recom-mended by Radio Shack when using their four-drive cable. The Teac drive I
used was loaned to me by American Business Computers. They give their Teac drives a one-year warranty. All the other disk drives were loaned by the manufacturer.
The Trak drive was another fast drive, requiring only 5 ms to seek a track. The card for the drive cable was even more inaccessible than the Teac drive, and to use it with the four-drive cable, it requires you to run the drive with the cover removed, use the last connector on the cable, or use a disk-drive extender cable, which costs about $10. It came with a single-drive cable already connected to it, so single-drive users won't need to get a cable when purchasing this drive. A nice feature of this drive is the disks are spring loaded. When you wish to remove a disk, you open the drive door and the disk springs out a half inch or so for easy removal. This is also the only drive with a power-on light as well as a drive-busy light.
The disk drives all worked reliably. I prefer the Percom drives because of the easy cable hook-up and relatively fast operation, but primarily because it was flippy. Nonetheless, all the drives worked well and deserve a recommen-dation.
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