Friday, November 14, 2014

Article Number: 9898


LIVING WITH DOS: DISK CACHES



by Barry Simon





Copyright (c) 1987, Capital PC User Group Inc.



This material may be republished only for internal use



by other not-for-profit user groups.





Posted on Compuserve with permission of CPCUG. May not be



reproduced without including the above copyright notice.





Published in the March 1987 issue of the Capital PC Monitor;



discussion of extended memory has been changed from the published



article.







I/O, I/O, Its Off to Work We Go!





There is much noise made about running 286 based machines at 8, 10



or even 12 Megahertz. While running your computer's



microprocessor at a faster speed will make a difference, for many



tasks the difference is bounded because the limiting factor is



often the speed of your input and output devices known



collectively as I/O. That these devices slow down the CPU is seen



by the typical times involved. 8 MHz means that the CPU goes



through 8 million cycles per second. Since a single instruction



on the 80xx family of chips takes from two to over twenty cycles,



a CPU in the current generation of MS-DOS machine can run at



roughly 1 MIPS (millions of instructions per second).





Memory chips are rated at speeds of 70-200 nanoseconds. A



nanosecond is a billionth of a second which means that such chips



are capable of speed comparable to CPU speeds. That the speeds



are slightly less is shown by the need for "wait states", which



slow down the CPU to allow access to memory at its speed; RAM



speeds, however, are roughly equal to those of the CPU. I/O



speeds are considerably less. Even a fast hard disk rated at 20



milliseconds has a rated speed 100,000 times the speeds associated



to RAM. Of course, because the RAM speed is a statement about



each access and hard disk access times involve the first access of



a disk sector, the actual ratios are not that bad.





But memory access, even by slow memory chips, is much faster than



even speedy hard disks; diskettes are even slower. While disk



transfer rates are slower than RAM exchanges, they are speedy



compared to output through parallel or serial ports, where



transfer rates are measured in 100's of bytes per second. (1200



baud, for example, means roughly 120 characters per second.) And



your console, the name for the combined keyboard/monitor I/O



device must interface the computer's slowest component -- you;



its speeds are often the slowest of all.





There are software tools to try to speed up I/O especially by



using RAM for certain operations. This month, I'll discuss one



category of those tools -- disk caches; programs that can



substantially speed up disk access.





In this article, I discuss six commercial and one shareware disk



cache programs; the programs are:





o Emmcache, a shareware product by Frank Lozier;





o Lightning from the Personal Computer Support Group;





o Polyboost from Polytron;





o Quickcache from Microsystems Developers, Inc.;





o Speedcache from FSS Ltd;





o Super PC-Kwik from Multisoft Corp.; and





o Vcache from Golden Bow Systems.







What Is a Disk Cache?





Disk caches are based on the idea that you are likely to want to



access a file that you accessed recently. This is not only true



for obvious data files like a database which you might search



several times in a row, but also for program overlays and for the



files that DOS often consults to locate other files: the FAT and



the various directories, especially the root directory.





Thus every time that a file is accessed, a cache will keep a copy



of that file in memory set aside especially for that purpose.



Since this special memory is limited, the cache has to have an



algorithm to decide which parts of the cache to clear out to make



room for new sectors. All the caches under discussion use the



algorithm of discarding those parts of the cache which were least



recently accessed; that is, not the ones that were first read the



longest ago but rather than ones which were needed longest ago.



Whenever DOS calls for a sector from disk, the cache program



intercepts the call to check if the requested material is in the



cache memory. If it is, the copy in memory is used and a disk



access is saved. A cache can avoid anywhere from one-third to



two-thirds of your disk accesses. To allow a large cache, it is



natural to put the data part of the cache (that is, the copies of



the sectors which were read rather than code that controls this



data) in extended or expanded memory.





For safety's sake, you would not want these programs to delay



writing to disk material that DOS wants to write to disk; this is



called keeping dirty buffers and none of these programs keep dirty



buffers. However, as I'll explain, DOS does some of its own disk



caching and it does keep dirty buffers which can produce problems.





Do not confuse keeping dirty buffers, that is delaying writing to



disk, with caching writes. The latter means that the cache writes



to disk but keeps a copy of the material which is written to disk



if it is different from the copy that was read previously. For



example, if you load a file in your word processor, change it and



save it, a program that caches writes will save a copy of the



final file version in its cache while one that does not, will not



keep such a copy. All the commercial programs discussed in this



article cache writes, but Emmcache does not.





When I first started using a cache, I found the experience eerie.



I'd do some action that I often did and wondered why my disk



access light wasn't going on.







Types of Memory





In our discussion of caching, various references will be made to



the different kinds of memory that are available to microcomputer



users. These include:





o Conventional memory, the 640K of Random Access Memory (RAM)



that is readily accessible by most 8088/8086/80186 computers.





o Extended memory, the memory above 1 megabyte (up to 16



megabytes) that is accessible by 80286 computers. This memory



is not normally accessible for use as conventional memory but is



generally used for RAM disks, disk caches or print spoolers.





o Lotus/Intel/Microsoft Expanded Memory Specification (LIM EMS) and



supporting memory boards (up to 8 megabytes) are paged in and out



of conventional memory, thereby providing the user with additional



memory for supported software.







Not a Memory Cache





You should be careful to distinguish between a disk cache and



memory caches. There are circumstances where it may happen that



some of your RAM runs at a higher speed than most of your RAM. In



that case, it may pay to cache some of the reading of instructions



from the slow RAM to speed up programs with loops. Two situations



are where you add a speedup (usually 80186- or 80286-based) board



to a PC with lots of old RAM typically at 200 nanoseconds or with



386 machines where RAM that keeps up with the processor should be



rated at 100 or even 70 nanoseconds. In any event, these



situations involve a memory cache, not a disk cache which is the



subject of this article.







Caches Versus RAM Disks





You can also cut down on access to a physical disk by using a RAM



disk, that is by setting aside a part of RAM as a virtual disk



which DOS accesses as if it were an ordinary disk. There are



several differences between RAM disks and disk caches. Accessing



files from a RAM disk is often slightly faster as our time tests



will show. Moreover, the first access of a file with a cache will



be slower than later accesses. On the negative side, you must



decide in advance which files you'll want on the RAM disk; you'll



also have to be sure to copy any changed data files from the RAM



disk to a real disk or risk losing them when you power down or if



your system crashes.





Which should you use? That depends on how you use your computer.



If you only use a few programs without extensive data files, a RAM



disk is probably better if you can make one large enough to hold



what it needs to. In other circumstances, a cache may be



preferable. If you have the RAM, there may be sense in using



both: a RAM disk for your common programs and a cache to take up



the slack. Most of the cache programs have built-in procedures



to avoid caching programs from the RAM disk, allowing you to save



valuable cache space for files from your physical disks.







Read Ahead





Many caches will "read ahead", that is, read in an entire track



whenever any reading takes place. If your files are large and not



fragmented, this can give you a real speed advantage but if not,



your cache will fill up with unused material. On a hard disk



with many isolated bad sectors, read ahead can actually slow down



disk access because of phantom disk errors. Lightning, Super



PC-Kwik, and Vcache have read ahead while the others do not.



Super PC-Kwik has the advantage of having read ahead as an option



that you can turn off. The makers of Polyboost maintain that



since most hard disks have errors and fragmented files, their



lack of read ahead is a gain over the competition, but I think it



will depend very much on your individual setup. In my own case,



for example, I have turned read ahead off when running on my main



machine because of the isolated bad sectors on my hard disk.







Are Caches Dangerous?





If your word processor fouls up a file write, all you are likely



to lose is the file you wanted to save. Typically, the files in



your cache include the FATs and root directories of your disks.



If these go bad, you are likely to have real problems getting to



any of the data on your entire disk. There are various tools



which can help you recover from such a disaster, but they may not



always work. This means that caches have an inherent danger to



them. Of course, since DOS is also writing these files all the



time, you could make the argument that caches are no more



dangerous than DOS; perhaps even less so, since DOS keeps dirty



buffers.





I cannot answer the questions about whether disk caches are really



dangerous. I can report that I've met several users who are sure



that problems they've had with FATs were caused by cache programs.



This may well be true, although it is also true that if you have



any problems with the logical structure of your disk and you have



a cache, you are likely to blame the cache. During the testing of



cache programs which went over six months, I lost the contents of



one of my hard disks three times. Two seemed to be hardware



problems solved in one case by a low level reformat and in the



other by a disk replacement. But the third one involved a piece



of software crashing the system; after rebooting, the root



directory on the hard disk was chopped liver. I'm suspicious that



the culprit was the cache I was using but maybe it was DOS' dirty



buffers or the program that crashed in the first place. All I can



say is that caching may be risky. You should be sure to back up



often but especially so if you have a cache. In fact, unless you



are willing to back up regularly, I recommend strongly against a



cache. On the other hand, caches are rather useful. I'm still



using a cache in spite of the problems that I had and some of



those who are certain that they had cache related problems are



still using them. And I've met people who feel that caches are



among their most important utilities.







Non-standard Setups





Because of the inherent dangers in caching and because caching



involves modifications of the disk BIOS, you need to be extremely



careful if your disk setup is non standard. You may need to



consult the vendors. Super PC-Kwik explicitly says not to use it



if you have a Bernoulli Box while Vcache says that it supports



these devices. The publishers of Vcache warned me not to use



Vcache with my 60 Meg Priam disk which I partitioned with Priam's



software into two 30 Meg drives; only large disks handled with the



VFEATURE program they they publish are compatible with Vcache. On



the other hand, Super PC-Kwik warns against disks with non-



standard sector sizes but said that it should work with software



making multiple standard DOS partitions. I was warned that they



had not tested the program with the Priam software but I can



report that it worked perfectly. Here, my advice is to check with



the publishers, be sure that you are backed up and run CHKDSK



several times a day when you first try a caching program with



anything non-standard.





With these programs, you cannot cache a network by having a cache



on your work station although you can sometimes cache the network



disks with a cache on the server. These are complex issues and



before attempting to use caches on machines connected to LANs,



you should be sure to speak with both the cache vendor and the



network vendor.





There is a second warning that needs to be made about using these



programs with AT extended memory, an option that is only available



with Polyboost, Super PC-Kwik and Vcache. Unfortunately, there



is no memory management protocol for AT extended memory provided



by the current versions of DOS. This lack of a standard means



there is potential for programs that you try to load there to not



know of each others existence and to therefore overwrite each



other. Since IBM publishes the source code for VDISK, all these



programs know about its protocol and can avoid clobbering it.



The situation is not so good for other virtual disk programs.



I've seen complaints about problems with AST's SUPERSPL program



and I've had problems with a cache in extended memory overwriting



a RAM disk set with the RAMDRV program included with Microsoft



Windows and with some versions of MS-DOS. It is unfortunate that



Microsoft has not published the specifications that this program



uses to access extended memory. So, if you are using any other



programs in extended memory and using an extended memory cache,



be sure to check out the operation of the other programs after



the cache is loaded. Super PC-Kwik and Vcache have a command



line parameter which you can use to give the program an absolute



address in extended memory at which to load and so avoid the



conflict "by hand". That they have to resort to such a kludge



speaks to the rather sorry state of extended memory support in



DOS 3.x.





A second aspect of caches in extended memory is that access of



extended memory involves features in the ROM BIOS that are not



often used in the current generation of AT software. Thus, the



operation may be improper on some AT clones. In fact, Vcache



comes with a program to test the BIOS access of extended memory.



If there is a problem, the clone maker must correct it.



Given the advent of a DOS that will access extended memory, it is



essential to get such problems rectified.





Two of the programs Speedcache and Quickcache load as device



drivers rather than as com files. Conventional wisdom would hold



that device drivers are somewhat less prone to compatibility



problems but I don't know if that is valid in these cases.







Use Your Free Cache





If you don't purchase and use one of these stand alone caching



programs, you should at least be sure to make use of the free



cache that comes with DOS. The cache size is set in units of 512



bytes called buffers. The default number, which DOS uses if you



don't specify otherwise, is two for 8088 machines and three for



80826 based machines; both are woefully inadequate. To increase



the number of buffers you must include a line





buffers=nn





in your config.sys file. Here nn is the number of buffers that



you want and the recommended numbers tend to be from 15 to 20.





Why not take buffers=99? The algorithms that DOS uses are not as



efficient as those in commercial caches so that the time it takes



to search the buffers to see if the proper sector is in the buffer



negates the time saved once the number of buffers becomes too



high.





What are the disadvantages of using buffers for a cache? First



there is the issue of dirty buffers. Actually, just using a



commercial cache doesn't effect this since caches still use DOS



for reading and writing and so the DOS buffers will still get



used. However, a cache that lets you decrease the number of



buffers that you use will force DOS to write its buffers to disk



more often because of space considerations. Another disadvantage



of DOS buffers is that since it is based on 512 byte chunks, if a



program requests more than that at once, DOS will always go to



disk and not check to see if the request is residing in its



buffers. Finally, there is the size issue that I mentioned; for



really large caches, you'll need a commercial program.





In short, if you don't use a commercial caching program, be sure



to put a line like





buffers=20





into your config.sys file.







Parameters





Once loaded, cache programs act in the background and require no



action or input from the user. But some of these programs have



option switches which you'll need to study carefully to load the



program to operate in an optimal manner. For many, the defaults



will be correct, but you'all at least want to adjust the cache



size.





What is the proper size? That's a trade off-between what else you



want to use your RAM for and how you use your machine. I have the



impression that unless your cache is at least 60K, you may be



better served by DOS buffers although for some operations, a 20K



cache will show a noticeable improvement.





Lightning has the annoying feature of using EMS memory if you have



it, even if you'd prefer to use conventional memory; it does not



support AT extended memory. As the name implies, Emmcache uses



only EMS memory. Speedcache supports the special bank switching



protocol on the Tall Tree JRAM boards as well as conventional



and EMS memory. For the other programs, you'll have to decide



whether your cache will reside in conventional, EMS or AT extended



memory and how much memory it will take. Be warned that some of



the programs default to rather unreasonable values of cache size,



such as all the remaining EMS memory or all the conventional



memory except for 232K for your remaining programs. Other



parameters vary from program to program and concern things like



what drives to cache and what algorithms to use in specific



cases. For all but the what and how much memory to use, you can



probably get away with using the defaults initially.





Super PC-Kwik has many switches and it may pay to vary some of



the switches and do some testing if some aspects of performance



seem below what you expect. For example, on the Kaypro 286i,



changing the diskette parameter from the default /d+ to /d-



resulted in an improvement of the diskettes test by a factor of



more than 4!







Memory Usage





Table 1 shows memory usage of the cache; it lists the amount of



conventional memory used by the control part of the software



exclusive of the memory taken by the cache. If you put the cache



in conventional memory, the amount in this table will be



overwhelmed by the amount of memory taken by the cache itself



but, if you place the cache in EMS or extended memory, this



figure will be quite important. For some of the conventional



memory caches, you pick only the total size of cache plus



controlling code. For these, the amount of memory in the control



part cannot be determined; these are indicated in the Table with



an *. All numbers are in kilobytes except for the first row.



For those that allow you to decrease the number of DOS buffers,



the second row can show a rather significant savings. The



figures for diskette cache give the amount needed to cache two



diskette drives; for several of the programs, diskette caching is



automatic and this amount is then listed as zero. Polyboost



suggests that you won't need to cache diskette drives if you have



a hard drive; depending on your mode of operation, that may be



true.





All the programs except for Polyboost will cache several hard



disks from the same cache with only one loading of the control



software. Polyboost requires multiple loading of its hard disk



cache which has two unfortunate consequences: you double the



overhead involved with the cache control software and you must



dedicate memory as associated with either one hard disk or the



other; this isn't useful if you tend to work on one hard disk for



a while and then switch to the other. Polyboost's caching is



limited to two hard disks. Two of the programs, Quickcache and



Speedcache, use an "advanced" EMS call not supported in the



current version of the Xebec Amnesia board software which I was



using; therefore, I am not able to report their memory usage. In



this instance, Speedcache printed an error message and exited



without loading and Quickcache crashed the system.





(Table 1 goes here)







Time tests





Table 2 shows the results of time tests. The tests are intended



to be "real world" tests. Tests 1-4 are tests of cache read



functions. Test 1 is the time to sort a 140K database that I



had just sorted a different way. This demonstrates the savings



you would get from repeated access to a database. Test 2 is the



time to spell check a 40K document through the first pass which



checks for possible misspellings. Test 3 is the time it took to



convert a 500K database from one version of a database I had to



another. Test 4 is the time to compile, link and EXE2BIN a 100K



file which I had just treated by MASM, LINK and EXE2BIN on a hard



disk and edited. This is typical of a situation where you may



get a compiler error, correct the source file, and then



recompile.





Test 5 and 6 test the ability to speed up disk writing. Test 5



is a PC Magazine "write random sectors" test. This test writes



the same data repeatedly to sectors which may be the same and so



it is particularly sensitive to the trick that caches use of



suppressing a rewrite of identical data to what was earlier



written to disk. Test 6 is a patched version of test 5 which



writes different data each time. It was supplied to me by the



publisher of Super PC-Kwik but I think it is a more significant



test than the original test 5.





The remaining tests attempt to check cache overhead or special



elements and are not as significant. Test 7 is the time it took to



copy 10 files adding to 350K from a hard disk to a floppy and



test 8 is the same for a floppy to floppy copy.





Tests 9, 10 and 11 are Norton's disk test program on a hard disk,



1.2 megabyte floppy, and regular floppy, respectively. The



Norton tests are included because the results are so dramatic.



These dramatic speed increases over DOS are due mainly to read



ahead as can be seen by running Super PC-Kwik with this option



turned off. The copy tests check on whether there is time lost



because of cache overhead.





The three columns listing DOS nn are tests done with no cache and



nn buffers. Tests 1, 2, 4, 5 and 6 were also done from a 1



megabyte RAM disk and Test 3 using two 1 megabyte RAM disks. For



vague comparison purposes only, three other times are reported



within asterisks: The time for a Norton disk test on a 2.4 Meg



RAM disk (#9), and the times to copy the same set of files used



in Tests 7 and 8 from a hard disk to a RAM disk (as #7) and from



one RAM disk to another (as #8).





All the tests are done on a Kaypro 286i with a Xebec EMS board.



To check how much overhead EMS causes, I ran the tests for Super



PC-Kwik in both EMS and conventional memory. This overhead is



due to the lack of DMA support in EMS and not to the bank



switching. Since I could not get Quickcache and Speedcache to



run under this EMS setup, I did their tests in conventional



memory which gives them a slight advantage. I used the



recommended number of DOS buffers with buffers=20 in those cases



with no recommendation about decreasing the number of buffers. I



used 256K of cache. For all the tests but Tests 8, 10 and 11,



the cache was only hard disk for those programs (Polyboost,



Vcache) with separate diskette caches. For Vcache, I used a 240K



vs. 24K split between disk and diskette caches and for Polyboost,



which requires separate caches for each diskette, I used a 256K



hard disk cache and 16K for each diskette.





(Table 2 goes here)





First, the test results illustrate the importance of increasing



buffers above the default 2 or 3 if you are not using a cache;



they also illustrate that there is a break point where too many



buffers can hurt you. On things that caches do well (Tests 1-4),



caches are competitive with RAM disks.





On Test #1 which is the most typical application of a cache, the



cache programs all showed the same rather substantial gain. While



there is a some spread on the other figures, the read tests really



don't distinguish between the different caches. On writing, I'd



give the nod to Super PC-Kwik and note that none of the tests



adequately check for caching writes. The lack of this feature in



Emmcache made me lean towards Super PC-Kwik. While Super PC-Kwik



stands out as special in a positive way on writes, it also stands



out negatively on diskette copies.





While on the subject of time tests, I should mention that



Lightning allows you to call up a screen which tells you how much



time you have saved by using the cache. Its figures are pure



fairy tale! I found that often it told me that I'd saved time in



situations where I'd actually taken more time than using



buffers=20. Presumably, it was using some algorithm giving me a



comparison on some kind of slow 8088 based machine with buffers=2.



Super PC-Kwik and Vcache will give you the more accurate listing



of the number of accesses that have been from the cache as



opposed to disk accesses.







Screen Speedup





Polyboost and Vcache come with screen speedup programs;



Polyboost also has a keyboard speedup program which I did not



test. Table 3 shows tests that I did in typing the same 111K



file to the screen that I used in my earlier articles on console



software. RAW is a program which turns on DOS' raw mode (see



February Monitor). The tests with the CRTBOST and EGABOOST



programs that come with Polyboost are done with their optional



parameters set to 1 and to 5. Setting this parameter to 6 is



equivalent to setting it to 5 and turning RAW on. Setting the



parameter to 1 is recommended for most users. Times are given in



seconds. For comparison, times are given for some of the other



screen management programs that I have considered. Fansi Console



has a "quick" parameter which can be turned on and off.





(Table 3 goes here)







While the times on EGA/CRTBOOST are impressive, it has some bugs.



When EGABOOST was installed, even with its speed parameter set to



the slowest value (1), I was unable to change monitors on a two



monitor system with either DOS' MODE command or a public domain



program that I use. There are programs that require me to use



Fansi's capability to turn Q=1 on and off from BATch files. These



programs do not work properly with CRTBOOST at its highest



settings. You can change to a setting where they do work but only



with a menu driven utility. Finally, both CRTBOOST and VSCREEN



suffer from the defect that screen speedup can be a disadvantage



if you don't also have screen scrolling memory. I have not



tested all screen scrolling memory programs with these two speedup



programs but I'd expect at least some incompatibilities. Fansi



comes with its own screen scrolling memory which even supports



EMS.







Summary





Lightning comes in both copy protected and unprotected versions;



indeed, the price difference is so great that I'd call it



ransomware. Because you'll want to load the program as part of



your autoexec.bat and the copy protection is of the key disk



version, you will really need the unprotected variety. All the



other programs are not copy protected.





It seems to me that these programs, as a group, are somewhat



overpriced. They are subtle but not that complicated as can be



seen by the fact that the main programs are typically about 5K.



Indeed, in cost per byte, they may be the most expensive class of



programs on the market.





On the basis of time tests alone, it is difficult to pick one



among these programs. Your choice will have to depend on factors



like the amount of conventional memory they use, the particular



characteristics of your system as they relate to issues like read



ahead, and price.





Emmcache is a free program by Frank Lozier of Cleveland State



University. It is available to CPCUG members in a file called



EMMCACHE.ARC on the MIX BBS, (301) 480-0350.





Lightning is published by the Personal Computer Support Group,



11035 Harry Hines Blvd., #206, Dallas, TX 75229, (214) 351-0564.



The non-copy protected version is $89.95 and the copy protected



version is $49.95.





Polyboost is published by POLYTRON, 1815 Northwest 169th Place,



Suite 2110, Beaverton, OR 97006 (503) 645-1150 and lists for



$79.95. The package includes screen and keyboard speedup in



addition to the caching software.





Quickcache is published by Microsystems Developers, Inc., 214-1/2



West Main Street, St. Charles, IL 60174; it lists for $49.95.





Speedcache is published by FSS Ltd, 2275 Bascom Ave., Suite 304,



Campbell, CA 95008, (408) 371-6242 and lists for $69.95.





Super PC-Kwik is published by Multisoft Corp., 18220 SW Monte



Verdi, Beaverton, OR 97007, (503) 642-7108 and lists for $79.95.



Also available is a conventional memory cache called Personal



PC-Kwik for $39.95 and a cache without all the options and



"advanced support" called Standard PC-Kwik for $49.95.





Vcache, which includes the Vdiskette and Vscreen programs, is



published by Golden Bow Systems, P.O. Box 3039, San Diego, CA



92103, (619) 298-9349 and lists for $49.95.









³EMM ³ LIGHT³ POLYB ³SPCK ³ VCACHE ³SCACHE³QCACHE



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Recommended buffers ³ x ³ x ³ x ³ 5 ³ 15 ³ x ³ x



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Buffer memory saved ³ x ³ x ³ x ³ 7.5 ³ 2.5 ³ x ³ x



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Conv. mem cache 20K ³ NA ³ 2.7 ³ * ³ * ³ 4.2 ³ 7.5 ³ 9.7



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Conv. mem each add 16K ³ NA ³ 0.4 ³ * ³ * ³ 0.3 ³ 0.5 ³ 0.5



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EMS memory 256K ³ 7.1 ³ 19.0 ³ 9.1 ³ 12.5 ³ 8.4 ³ * ³ *



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄ



EMS mem each add 64K ³ 1.0 ³varies³ 1.7 ³ ~0 ³ 1.1 ³ * ³ *



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄ



EMS memory 1 Meg ³19.1 ³ 36.3 ³ 30.1 ³ 12.7 ³ 21.6 ³ * ³ *



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄ



AT Ext. mem 256K ³ NA ³ NA ³ 9.7 ³ 29.4 ³ 8.9 ³ NA ³ NA



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄ



AT Ext. each add 64K ³ NA ³ NA ³ 1.7 ³ 2.0 ³ 1.1 ³ NA ³ NA



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄ



AT Ext. mem 1 Meg ³ NA ³ NA ³ 30.7 ³ 43.4 ³ 22.1 ³ NA ³ NA



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄ



Maximum cache size (EMS) ³4 Meg³ 1536K³ 2200K ³1072K ³ 15 Meg³ ? ³2000K



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄ



2 Diskette cache 16K (con) ³ 0 ³ 0 ³ 34 ³ 0 ³ 25.9 ³ 0 ³ 0



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄ



2 Diskette cache 16K (EMS) ³ 0 ³ 0 ³ 5.4 ³ 0 ³ NA ³ 0 ³ 0



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄ



Able to load twice in error³ Y ³ N ³ N ³ N ³ N ³ N ³ N



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÄ





Table 1. Memory Usage of Cache Programs















³DOS 3³DOS 20³DOS 90³EMM³LIGHT³POLY³VCACE³SPCK³SCON³SCAC³QCAC³RAMDSK



ÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÄ



#1 ³ 19 ³ 19 ³ 19 ³ 11³ 11 ³ 11 ³ 11 ³ 12³ 11³ 10³ 10³ 12



ÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÄ



#2 ³ 43 ³ 38 ³ 39 ³ 37³ 36 ³ 38 ³ 37 ³ 35³ 32³ 35³ 34³ 33



ÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÄ



#3 ³1550 ³ 783 ³ 814 ³615³620 ³735 ³ 650 ³ 614³ 571³1065³ 704³ 642



ÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÄ



#4 ³ 86 ³ 80 ³ 82 ³ 75³ 75 ³ 77 ³ 75 ³ 73³ 73³ 75³ 75³ 73



ÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÄ



#5 ³ 18 ³ 20 ³ 20 ³ 13³ 3 ³ 3 ³ 3 ³ 5³ 5³ 12³ 2³ 5



ÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÄ



#6 ³ 18 ³ 18 ³ 20 ³ 13³ 13 ³ 12 ³ 12 ³ 5³ 5³ 12³ 11³ 5



ÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÄ



#7 ³ 45 ³ 31 ³ 30 ³ 31³ 30 ³ 28 ³ 32 ³ 41³ 41³ 29³ 27³ *4*



ÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÄ



#8 ³ 70 ³ 64 ³ 77 ³ 62³ 64 ³ 64 ³ 63 ³ 69³ 69³ 62³ 61³ *2*



ÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÄ



#9 ³604 ³ 500 ³ 535 ³465³671 ³476 ³ 585 ³ 490³ 371³ 451³ 453³ *20*



ÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÄ



#10³419 ³ 415 ³ 417 ³418³ 67 ³418 ³ 61 ³ 61³ 61³ 418³ 417³



ÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÅÄÄÄÄÄÄ



#11³ 92 ³ 91 ³ 91 ³ 90³ 36 ³ 81 ³ 36 ³ 37³ 37³ 91³ 89³



ÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÄ





Table 2. Time Tests on Disk Caches





EMM = Emmcache;



LIGHT = Lightning;



POLY = Polyboost;



VCAC = Vcache;



SPCK = Super PC-Kwik, all in EMS.





SCON = Super PC-Kwik;



SCAC = Speedcache;



QCAC = Quickcache, all in conventional memory.













º EGA w/o³ EGA & ³ Mono w/o³ Mono &



Program º RAW ³ RAW ³ RAW ³ RAW



ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÎÍÍÍÍÍÍÍÍÍÍØÍÍÍÍÍÍÍÍØÍÍÍÍÍÍÍÍÍØÍÍÍÍÍÍÍÍÍ



ANSI º 143 ³ 120 ³ 125 ³ 93



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄ



FANSI CONSOLE/Q=0º 105 ³ 74 ³ 76 ³ 44



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄ



FANSI CONSOLE/Q=1º 32 ³ 17 ³ 38 ³ 15



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FLICKER FREE º NA ³ NA ³ 34 ³ 13



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄ



NANSI º 104 ³ 66 ³ 74 ³ 38



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TALL SCREEN º 204 ³ 177 ³ 174 ³ 149



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VSCREEN º 90 ³ 74 ³ 61 ³ 46



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄ



POLYBOOST S=1 º 81 ³ 66 ³ 53 ³ 37



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄ



POLYBOOST S=5 º 30 ³ 13 ³ 25 ³ 10



ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÐÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄ





Table 3. Time in Seconds to TYPE 111K File


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