WHAT IS FAST2 AND HOW DOES IT WORK?
-----------------------------------
What is FAST2? It is a new transient program for the CP/M (*)
disk operating system. It was originally written by by Roger
van Valzpah and released by the CP/M user group as FAST. This
version was modified by David Bennett of the Alfred Hospital,
Melbourne to be compatible with CP/M version 2.0.
FAST2 is used in conjunction with other transients to speed up
their execution. Of course, nothing but a hardware change can
increase the rate at which your CPU executes instructions. But,
most transients are "disk bound", that is, they spend a large
percentage of their total execution time just waiting for the
information they need from the disk.
FAST2 uses this fact to increase execution speed by reducing the
time spent waiting for the disks. This is accomplished by using
two different types of buffering. Firstly, portions of the disk
which are frequently accessed (the directory) are held in a
buffer, eliminating the need to seek to read them. Secondly,
disk accesses are grouped together in time to reduce the amount
of time lost to rotational latency and head load delay.
HOW TO USE FAST2
----------------
The normal CP/M command to assemble a file with the name
MUMBLE.ASM is:
A>ASM MUMBLE
To perform the same function under FAST2, simply type:
A>FAST2 ASM MUMBLE
Thus, in its simplest form, FAST2 can be used as a prefix to any
normal CP/M command. This will load FAST2 which will link
itself to your operating system and allocate its disk buffers.
Then the transient ASM.COM is loaded and given control. The
fact that FAST2 is in the system is totally transparent to the
transient, except for the reduced memory size. Messages will be
printed just before and after the transient is executed to
indicate that FAST2 is in control. After execution, you should
see something like this on your terminal:
A>FAST2 ASM MUMBLE
Alfred Hospital FAST 2.01
CP/M ASSEMBLER - VER 1.4
1234
056H USE FACTOR
END OF ASSEMBLY
FAST terminated
A>
Where N.NN is the version number of FAST2 that you are using.
COMMAND LINE OPTIONS
--------------------
The buffering action of FAST2 may be altered with the use of
command line options. This is accomplished by following the
FAST2 command with an option string enclosed in square brackets
("[" and "]"). A valid option string must consist of a drive
specification followed by one or more buffering mode
specifications. This group may be repeated for buffering of
multiple drives. Examples of typical option strings will be
given below.
Explicitly specifying the buffering mode is desirable to reach
the best trade-off between speed of execution and memory usage.
In general, as more buffering is used, execution speed will
increase. However, more buffering means more memory usage.
The type of buffering selected should be tailored to the disk
usage patterns of the transient being executed. For instance,
write buffering will offer no speed improvement when a transient
only reads the disk.
One thing that FAST2 must know is which disk drive is to be
buffered. This is communicated to FAST2 simply by using the
single letter name of the desired drive (e.g. "A" for disk
drive A). As a convenience, the current default drive may be
specified with the commercial at sign ("@").
The second thing which FAST2 must know is which mode of buffering
is to be used. FAST2 supports three different buffering modes.
Each mode may be used individually or in combination with other
modes to offer the fastest execution. The three modes available
are:
Seek buffering
Read buffering
Write buffering
Yes (all of the above)
The type of buffering desired is communicated to FAST2 by a
single letter in the option string. The letter is simply the
first letter of the word which describes the type of buffering
(capitalized above). The operation and application of each mode
will be discussed below. Thus, a typical FAST2 command line
might look like this:
B>FAST2 [ASWBSR] ASM MUMBLE.BAA
In this example, the .ASM source file is on drive B so read and
seek buffering have been specified for that drive. The A drive,
on the other hand, is to receive the result of the assembly (the
HEX and .PRN files), so it gets write and seek buffering.
BUFFERING MODE DESCRIPTIONS
---------------------------
Seek buffering causes the disk directory to be read into a buffer
the first time a drive is accessed. From then on, all reads
from and writes to the directory can be carried out without
moving the disk head from its current position. Thus,
transients which access the directory frequently will be sped up
considerably by seek buffering. Transients which fall into this
category are those which deal with many different files
simultaneously, perform operations with temporary files and
rename them, read or write large (more than 16K) files, and those
which perform random disk I/O. In particular, ASM.COM, MAC.COM,
PIP.COM, and ED.COM are examples of such transients.
Read buffering causes an entire track from the disk to be read
into a buffer the first time any sector is read from that track.
This increases execution speed because CP/M typically reads most
of one track before going on to the next one. Additionally, the
time required to read a whole track is a fairly small percentage
increase over the time required to read a single sector. The
net effect is that less time is spent waiting for the rotational
latency of the disk. This mode of buffering is most beneficial
to transients which read disk files sequentially. As a matter
of fact, it may slow down transients which read files in a random
access mode. Fortunatlly, the vast majority of CP/M transients
read the disk sequentially. Examples of such transients are
ASM.COM, MAC.COM, PIP.COM, and BASIC-E.COM (if the BASIC program
doesn't do random I/O!!).
With write buffering, sectors that are to be written to disk are
held in a buffer for a time, instead of writing them immediately.
Sectors for any given track are held in the buffer until CP/M
tries to write to a track that is not buffered. When it is time
to change tracks, only those sectors which were changed are
actually written before clearing the buffers to make room for the
new data. This improves execution speed for the same reasons
that read buffering does, i.e. a whole track can be written in
about the time it takes to write a single sector. Transients
which benifit from this type of buffering typically write to disk
sequentially. Examples include ASM.COM, MAC.COM, and ED.COM.
DEFAULT PHILOSOPHY
------------------
Two of the qualities generally associated with a good program are
versatility and ease of use. FAST2 has been written with these
two qualities in mind as the primary design goals. Many times,
however, these two goals can be contradictory. A versatile
program is one which is capable of a wide variety of tasks or one
that fits many different FAST2 Default philosophy applications.
This usually means a program with many user selectable options.
Forcing the user to type the same frequently used options every
time a program is invoked or committing him to remember a long
list of options is contradictory to the goal of ease of use.
This conflict is resolved by the use of default mechanisms within
FAST2.
A default mechanism is simply a rule that can be used to make
assumptions about the user's wishes when he has not stated them
explicitly. Thus, versatility has been retained by allowing the
user the ability to specify options explicitly, while the default
mechanism frees the user from this tedium much of the time. In
short, defaults allow versatility and ease of use to peacefully
co-exist in the same program.
cp 3
DEFAULT MECHANISMS IN FAST2
---------------------------
There are two levels of defaults built into FAST2. The first
default mechanism is used when either the drive or buffering mode
is omitted from an option string. If a drive name is not given,
the default drive for CP/M is used (this is equivalent to "@").
If no buffering mode is specified, read and seek buffering are
used. Thus, the following two commands would be equivalent.
B>FAST2 [BRW] LOAD MUMBLE
B>FAST2 [RW] LOAD MUMBLE
And so would the following two commands.
A>FAST2 [BRS] PIP B:THIS=B:THAT
A>FAST2 [B] PIP B:THIS=B:THAT
The second default mechanism comes into play when no option
string is given on the command line. Instead of executing the
transient with no buffering, FAST2 uses a default option string
to specify the buffering used. This string is [@RS], giving the
user read and seek buffering on the default drive when no option
string is present on the command line. The user may, at his
option, alter the default option to one which is more suitable
for his typical uses. For instance, if you typically use FAST2
for assembling and don't have to worry about running out of
memory, a good default string would be [@RWS]. Conversely, if
you are running in a small memory system, a good choice would be
to change the default option string.
HOW TO CHANGE THE DEFAULT OPTION STRING
---------------------------------------
The default string is stored in FAST2 at address 0130H. Thus,
to change the option string, use SID or DDT to change the
existing string. Assuming you have SID this is very easy:
A>SID FAST2.COM
SID VERS 1.4
NEXT PC END
0A00 0100 94FF
#S130
0130 5B "[@RWS]
0136 20 .
#^C
A>SAVE 9 FASTX.COM
If you do not have SID, you'll have to use DDT and figure out the
hex for the ASCII string you wish to patch in. Then use the
Substitute command to patch the file as above. In either case,
test the patched file before killing the old FAST2.COM and
renaming the new file to FAST2.COM.
cp 3
WARNINGS N-E-V-E-R CHANGE DISKS WHILE EXECUTING UNDER FAST2!!!
And in case you missed that one I'll say it again...
YOU MUST
********** N-E-V-E-R N-O-T E-V-E-R **********
CHANGE DISKS
WHILE EXECUTING UNDER FAST2!!!
(not even if you think you know what you are doing)
Wait until you see the message "FAST2 terminated" before even
thinking about switching disks. A rather nasty side effect of
seek buffering is that it disables the disk change detection
mechanism built into CP/M. This means that you will NOT get the
warning message "Bdos error on A: R/O" if you forget and change
disks without booting. Instead you will get wild and
unpredictable effects possibly including destroying your disk
directory.
This also gives rise to a minor incompatibility with any
transients which use the BDOS reset function (BDOS call 13).
This function is used in transients which allow the user to
change disks without rebooting. Some examples are MBASIC,
CBASIC, WORDSTAR, and others. Fortunately they only this BDOS
function when an explicit command is used to permit changing
disks. FAST2 is compatible with transients of this sort as long
as no attempt is made to change disks.
One way to avoid trouble is to avoid using FAST2 with any
transient which requires user input. Any such transient, by
waiting for your reply, would leave you with the opportunity to
change disks. To minimise the risk of your running into trouble
with such programs, FAST2 watches out for any requests for user
input. When such a request is detected, FAST2 immediately writes
all modified blocks back to disk. While this gives some
protection against lost data, it fails with programs such as
Wordstar which monitor console status and only request input
after a key is struck. Again, DON'T change disks.
COMPATIBILITY
-------------
FAST2 is fully compatible with the following transients and can
be expected to provide a significant reduction in execution time.
CP/M utilities:LOAD, SUBMIT, DUMP, MAC
Compilers: ASM, MAC, RMAC, M80, FORTRAN, F80, COBOL-80,
PL/I, etc.
FAST2 is fully compatible with the following transients, but due
to the fact that they require user input, some caution should be
exercised when they are used with FAST2. As mentioned above,
stopping for input gives the user the chance to inadvertently
change disks which CP/M would not be able to detect. If the
user is able to guard against this occurrence, he may use FAST2
with these transients and expect a significant reduction in
execution time. In particular, the improvement in the speed of
PIP is little short of unbelievable.
FAST2 is fully compatible with the following transients, but due
to the way in which they access the disk, little or no speed
improvement can be expected.
Special utilities: SYSGEN, MOVCPM, FAST2, COPY
Due to an unfortunate memory dependency, STAT (version 1.4) does
not correctly report the number of bytes remaining on the disk
when it is executed under FAST2. This is no great loss because
FAST2 can do little to speed up the execution of STAT.
Best results are obtained in situations where the disk is
accessed sequentially, especially if large files are read from
beginning to end. The following examples indicate some of the
results which can be expected using standard single-sided single-
density 8 inch diskettes.
A>FAST2 [AYBY] PIP B:=*.*
This command can be expected to copy a 241k diskette full of
data, file by file, in about 80 seconds. With verification,
it takes perhaps 100 seconds.
A>FAST2 [ARBY] WS
Use this command on your Wordstar utility disk to edit text
on drive B: (but don't change disks!) and you will marvel at
the new version of your editor. It will load overlays in
the blink of an eye and save files (e.g. ^KS) in nothing
flat.
A>FAST2 [ARBY] COBOL CMUMBLE
The compilation for a small 100 line program drops from
about 90 seconds to less than 40. The biggest gains are in
loading overlays of the compiler.
A>FAST2 [ARBY] CBASIC BMUMBLE $BF
One of the most irritating features of this compiler is that
if you switch off the listing, you don't know which lines
contain any errors which are detected. Solution: save a
listing on disk and with FAST2 the compilation will still
take no longer than before.
FAST2 MESSAGES
--------------
During the course of execution, FAST2 may print any of several
different messages. Each of these messages is listed below
along with conditions under which it is printed.
Alfred Hospital FAST 2.01
This message is printed after the transient to be executed
under fast has been successfully loaded, but just before
control is transfered to it. This is simply an informatory
message and does not signal an error condition. In this
message, N.NN is the version number of FAST2 which you are
using.
FAST terminated
This message is printed after the transient has finished
execution and all disk buffer
s have been emptied. This too
is simply an informatory message printed under normal
conditons.
NO COM FILE
This message is printed when the transient filename given on
the command line cannot be found in the directory. No
recovery action can be taken, so the execution complete
message is printed and FAST2 re-boots.
OUT OF MEMORY
This message is printed when the size of the TPA is exceeded
while allocating buffers or while loading the transient.
In either case, no recovery action can be taken, so the
execution complete message is printed and FAST2 re-boots.
There are several solutions to the out of memory problem:
use less buffering, use smaller transients, or, of course,
buy more memory.
DISK WRITE ERROR
This message is printed when FAST2 attempts to write data to
disk and gets the unsuccessful completion flag back from the
BIOS. The only recovery action taken is simply the
printing of the message, then execution continues normally.
This usually indicates a serious error (like a protected
disk) and the user should boot and take corrective measures
as soon as possible.
INVALID OPTION
This message is printed whenever an error is detected in the
option string being scaned by FAST2. This may be the
option string supplied on the command line or the default
option string in memory in the unlikely event that it has
been incorrectly modified. Some examples of invalid
options are the null option ([]), options containing invalid
characters ([Q]), or options which specify buffering of the
same type for the same drive twice ([ABA]).
MEMORY HIT
This message is printed whenever FAST2 attempts to write to
a memory location and cannot read the data it has just
written. The recovery action taken is to print the message
and ignore the error. It is usually an indicator of
hardware problems in your system and should be looked into
immediately. If MEMORY HIT errors are persistent and you
have a ROM monitor in your system, you can use FAST2 to help
find the memory at fault. Create a special FAST2.COM with
a jump to your monitor patched into location 521H. This
location is called when a memory hit is detected. The HL
register contains the address of the bad byte and a bit in
the A register is set for each bad bit in memory.
MEMORY ALLOCATION
-----------------
When FAST2 is loaded, it automatically relocates itself to the
top of the TPA (just like DDT and SID). This action overlays
the CCP. A side effect of this is that transients which
normally return to the CCP without booting will boot when
executed under FAST2. An example of such a transient command is
LOAD.
As mentioned earlier, the only way a transient can tell that it
is being executed under FAST2 is that the size of the TPA is
decreased. The amount of memory taken out of the TPA by FAST2
is dependant on the number of buffers which are allocated.
cp 4
The formulas used to determine the amount of memory used
are:
buffers = NTB * (3 + 131 * SPT) + NSB * (3 + 131 * SID)
SID = NDE / 4
mem used = 768 + [buffers]
Where: NTB is the Number of Track Buffers allocated
SPT is the number of Sectors Per Track
NSB is the Number of Sector Buffers allocated
SID is the number of Sectors in the Directory
NDE is the maximum Number of Directory Entries
[ ] indicate rounding up to the next multiple of 256
For a normal 8 inch IBM compatible version of CP/M, all these
computations can be replaced by a simple estimating rule: Allow
1024 bytes for FAST2 code overhead, 3409 bytes for each track
buffer (R or W), and 2099 bytes for each seek buffer (S). As an
example, FAST2 executed without a command line option string will
use 1024 + 3409 + 2099 bytes. If this sum is rounded up to the
next multiple of 256, the actual memory usage figure becomes 6656
bytes. The maxmimu on a two drive system is the command option
[AYBY] which costs 1024 + 4x3409 + 2x2099 or a total of 18.5K
(18944 bytes).
