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--------------------------------- part 2 of 4 ------------------------------

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Section 2: Upgrades and Expansion

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Q2.1) What are the memory limits of the various Acorn machines?

For the most part the 8 bit machines were limited to a maximum of around 256k of memory. Although various expansion systems including second processors effectively meant the upper limit was about 1 Meg. (Although I have been told of a second processor with 4 Meg of memory in it. ) For the early 32 bit machines the upper limit currently is 16 Meg of memory. Not all of the range of machines are capable of this however and the list looks something like this:-

A3xx - 8 MB maximum through third party, 1 MB official limit.
A4xx - 8 MB maximum through third party, 4 MB official limit.
A4xx/I - 8 MB maximum through third party, 4 MB official limit.
A3000 - 8 MB maximum through third party, 2 MB official limit.
A540/R260/R225 - 16 MB maximum.
A5000 - 8 MB maximum through third party, 4 MB official limit.
A4 - 4 MB official limit.
A30x0 - 4 MB official limit.
A4000 - 4 MB official limit.
A5000 - 8 MB official limit. (alpha variant of the A5000)
A7000 - 128 MB + memory on mother board. (Tops out at 132 MB and requires a 128 MB SIMM to do it.)

Newer RiscPC machines have an official upper limit of 256 Mb, plus 2 MB of VRAM, on all models. However this does require you using 128 MB SIMMS.

If you add the Kinetic StrongARM upgrade (available from Castle Technology) then this upper limit can be expanded further because the Kinetic card contains either 64MB or 128MB SDRam on board. Further information on the Kinetic card is available from Castle Technology (http://www.castle.org.uk).

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Q2.2) What is a second processor and what second processors are there?

A second processor was the generic name for a range of parasite processors that could be linked to Acorn's original 8 bit machines via what was called the `Tube` interface. Basically the host machine became dedicated to handling the Input and Output while the second processor would do the higher level functions (like running your programs). The second processor ran asynchronously to the host processor allowing incredible increases in execution speed for programs. A wide range of processors were supported t
his way allowing Acorn's eight bit range of machines to remain viable and useful for much longer than their technology would suggest.

The Second Processors that existed are :-

Z80 second processor.
6 MHz RAM.
64k Memory.
CP/M OS.
External second processor for all eight bit machines.

* 6502 second processor.
3 MHz RAM.
64k Memory.
Extended version of the BBC MOS.
External processor for all eight bit machines.

32016 second processor.
6 MHz RAM.
256k-4096k Memory.
Panos.
External processor for all eight bit machines.

ARM 1 second processor.
4 MHz RAM. (At a guess...)
4096k Memory.
Brazil OS.
External processor for all eight bit machines.

6502 co-processor. (internal second processor)
4 MHz RAM.
64k Memory.
Extended version of BBC MOS.
Internal processor for Master 128 machines but could be fitted external to the other eight bit machines.

80186 co-processor.
10 MHz RAM.
512k Memory.
DR-DOS+ with GEM.
Internal processor for Master 128 machines but could be fitted external to the other eight bit machines.

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Q2.3) Can PC VGA & Multisync Monitors be added to an Acorn machine?

It depends on what monitor you have, and what Acorn machine you have. There are two main types of PC VGA monitors out there...

TYPE="1"
--------
* Fixed Frequency - These monitors will only display video signals with certain line and refresh rates. They will typically only display CGA / EGA / VGA modes.

* Multi Frequency - These monitors will display any video signal within a certain range, typically 30-50Khz line rate and 50-80Hz refresh rate.

Type 1 almost always require separate syncs as the monitor uses the polarity of the syncs (mainly positive going negative or mainly negative going positive) to determine what the line and refresh rate should be.

Type 2 vary. Some require separate syncs (vertical and horizontal) and others will work with composite syncs (vertical and horizontal EOR together).

As PC monitors typically start at a line rate of 30Khz compared to the TV broadcast modes (mode 12 etc.) that have a line rate of 15Khz, VIDC has to do more work to obtain a 30Khz line rate.

This means that you computer will slow down slightly if you use a 30Khz+ line rate monitor. If you have an ARM 3 fitted such slow downs will probably be negligible.

Now, depending on what type of Archimedes you have depends on what type of monitor you can use.

A540 / A5000 / A4 / A3010 / A3020 /A4000
----------------------------------------
Has software control over the polarity of the syncs and what frequency VIDC is clocked at.

The A540 with RISC OS 2 can only use modes 26-28 (640x480) and 31 (800x600). However, by changing links and a *configure option, you can get the computer to generate separate syncs with no problem.

The other machines with RISC OS 3 can do even better. If you tell the computer that you have a VGA monitor it will re-map all of the 15Khz line rate modes up to 30KHz line rate. This means that you can play your games that require mode 12 / 13. However, as a PC monitor is designed to display 320 lines minimum then you will get a 'letterbox' effect as mode 12 has only 256 lines.

All these machines have 24Mhz, 25.175Mhz and 36Mhz crystals to drive VIDC with. The 25.175Mhz crystal is needed to obtain the correct video rates for PC monitors displaying 640x480 screens. The 36Mhz crystal is used to obtain higher resolution modes, like 800x600x16 colours.

A3000
-----
This can generate separate syncs but requires links to be set to determine the polarity. It has only a 24Mhz crystal and can therefore only drive 'forgiving' monitors correctly that don't mind the 640x480 video mode timings being slightly incorrect.

The links to change, to set the sync polarity, are as follows:
Link 24: Change from SOUTH to NORTH
Link 25: Change from OPEN to CLOSED

In order to obtain proper timings, and software control of the sync polarity, you will need a VGA VIDC Enhancer for the A3000.

A400 series
-----------
The situation gets more complex. Due to an 'error' in the PCB / circuit diagram, the A400 series cannot generate separate syncs satisfactorily.
The video signal loses the green component when separate syncs is selected. It has been reported to me that 400/I series machines can have this fault corrected by cutting pin 3 of IC9.

As standard, there is no polarity control over the syncs. In common with the A3000, there is only a 24Mhz crystal. Also it is links 1 and 2 that need changing.

If the PC monitor can handle composite syncs then the monitor can be used in 640x480 mode only.

A300 series
-----------
Most, if not all, of the A300 series had the circuit board hardwired into composite mode continuously. There is only a 24Mhz crystal, and only composite sync monitors can be used. Also the A300 suffers the same problem as the A400, it looses green component in separate sync mode.

However I am told that it is possible if you are prepared to alter the hardware, by fitting a three pin header to both LK10 and LK11 (sited near the RGB connector). Cut the track which connects the middle pin to one of the outer pins of each header. Place a link between the middle pin and the other pin for each header. Finally configure sync to 0 and monitor to 3 to inform RISC OS of the change and you should have separate syncs.

Even after these changes it may be required to cut pin 2 of IC4 to remove the composite sync off the green signal. Some SVGA monitors in particular are fussy about this.

RiscPC series & A7000/A7000+
----------------------------
This has a very flexible VIDC in it and is quite capable of driving PC monitors with no trouble.
N.B. The Risc PC can sometimes get confused when set to 'auto' monitortype, resulting in a blank screen and no display on the monitor.
If this happens, try re-configuring the CMOS ram settings to the following and then reseting the machine.

*Configure Monitortype 4
*Configure Sync 0
*Configure Mode 40

This should prevent the monitor confusing the auto setting of the Risc PC.

However to connect an older machine (A3000,A300,400 series) to a VGA monitor, you will need a means of connecting the standard 15-pin VGA plug to the 9-pin socket in the computer. A number of companies sell 'converters', but all this boils down to is a lead with the following configuration :-

.------------------------. VGA 15-pin socket
\ 1 2 3 4 5 /
\ 6 7 8 9 10 /
\ 11 12 13 14 15 /
'------------------'

.------------------------. Arc 9-pin plug
\ 1 2 3 4 5 /
\ /
\ 6 7 8 9 /
'------------------'

Signal VGA pin Arc pin

Gnd 10 9
Red 1 1
Green 2 2
Blue 3 3
R gnd 6 6
G gnd 7 7
B gnd 8 8
H 13 4
V 14 5

In conclusion, apart from the A5000 and newer machines, no computer as standard can drive either a fixed frequency or multi-frequency PC monitor in all of the Archimedes modes satisfactorily. However VIDC enhancer boards can be bought to upgrade an Archimedes series machine to handle the needed timing and signals.

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Q2.4) Are there any Acorn cards for IBM PC or compatible machines?

Yes. Three cards in total :-

Springboard
ARM 2 processor, 4096k Memory, 8 MHz RAM, Brazil OS.

PC ARM development system
Precursor to Springboard. Hardware functionally identical.

Ecolink
An econet link card for the PC.

However, to the best of my knowledge none of these cards are commercially available.

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Q2.5) What is a VIDC enhancer? Will I need one for my new multisync monitor?

A VIDC enhancer is basically a clock change for your VIDC. Most Arcs (bar the A540 and newer machines) have 24 MHz VIDC chips installed in them. A VIDC enhancer increases this to 36 MHz allowing much higher resolution screen modes to be displayed on your Arc. (800x600x16 or SVGA standard becomes available.) You do not need one to use a Multisync monitor - the standard VIDC handles that just fine. However having a VIDC enhancer is only really useful if you do have a Multi-sync monitor.

A 'build-it-yourself' VIDC enhancer is available from http://www.mirror.ac.uk/collections/hensa-micros/local/riscos/drivers/autovidc.arc and Maplin Electonics supply 9-15pin converters for around Ł6.00

Note a VIDC enhancer is unnecessary and incompatible with the RiscPC range of machines.

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Q2.6) What configuration of serial cable should I use for modem work?

Here follows a diagram of the necessary connections for common terminal programs to work properly. They are as far as I know the informal standard agreed upon by commercial comms software developers for the Arc.

Pins 1, 4, and 8 must be connected together inside the 9 pin plug. This is to avoid the well known serial port chip bugs. The modem's DCD (Data Carrier Detect) signal has been re-routed to the Arc's RI (Ring Indicator) most modems broadcast a software RING signal anyway, and even then it's not really necessary to detect it for the modem to answer the call.

Arc (9 pin) Modem (25 pin)
----------- --------------

9---RI-------------------------DCD----8

Of course you can connect the Modem pin 20 to any one of pins 1, 4, or 8 on the Archimedes plug, as they are all connected together anyway.

Chocks Away Extra Missions (the flight simulator from 4th Dimension) suggests that the serial cable be wired as above except that pins 1-4-6 are connected together and the modem's CTS (pin 5) be connected to the Arc's pin 8 (ie the connections at pins 6 and 8 be swapped over at the Arc's end). This has been tried and it also seems to work fine.

However newer Arc's like the A5000 have come out (and indeed the occasional A310) with a `corrected` serial port. This newer serial port operates as it should and is directly compatible with standard PC cables.
Older comms software about do not take this in account and assume that you have a cable patched in the manner described above. If you do not use such a patched cable on these `fixed` serial ports this software will generally fail to work completely. (Usually hardware flow control fails.)

With the advent of the Risc PC a standard PC cable is advised.

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Q2.7) How can I get unfiltered sound from an Acorn machine?

All Acorn machines are equipped with a sound filter designed to remove high frequency harmonics from the sound output. However this does cause a muffled feel to the sound as on some machines the filter is a little too excessive and it filters out valid frequencies. Also the filter is optimised for 20.833 kHz output and has less desirable results when the output rate is changed. Accordingly people who do audio work often want to bypass the filter.

On all machines bar the A3000 there is the Internal Auxiliary Audio Connector (usually called link LK3), which can be easily plugged into to provide the unfiltered output. This connector has 10 pins on it and is usually found near the headphone socket on the motherboard. The pins are :-

1 Unfiltered Left
2 Ground
3 Filtered Left
4 Ground
5 Auxiliary Input
6 Ground
7 Filtered Right
8 Ground
9 Unfiltered Right
10 Ground

Simply hook into the Unfiltered outputs.

On an A3000 you need two 10uF 16V ALEC capacitors. Look for chip LM324 (IC39) and hook the capacitors like this:-

Pin 1 --> --|+ |--- Unfiltered Left
Pin 2 --> --|+ |--- Unfiltered Right

The Risc PC & A400 machines have a connector similar to the A5000.

There are several caveats to this procedure. Opening your machine may void your warranty and most definitely should not be attempted if you are unsure of the procedure. Do not unplug/plug the unfiltered audio output while the machine is turned on, by bypassing the filter you also bypass the normal protective circuitry for the audio output.

Finally you will hear higher harmonics present in the audio signal so you will need to connect the signal to a filter of some kind to reduce this extra noise.

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Q2.8) Can I connect a SCART monitor to my Acorn machine?

If you have an older Acorn machine with a nine pin video socket, then yes and here is the wiring diagram :-

.------------------------. Arc 9-pin plug
\ 1 2 3 4 5 /
\ /
\ 6 7 8 9 / Case
'------------------'
_____________________
|19 1| SCART 21-pin plug
| | | | | | | | | | | |
/ |
/ | | | | | | | | | | |
/___20_________________2_| 21 (metal casing)

A SCART connector is also known as a Euroconnector or a Peri-Television connector.

Arc SCART
Case | ------------- 21 Case
Red 1 ------------- 15 Red
Green 2 ------------- 11 Green
Blue 3 ------------- 7 Blue
CSYNC 4 ------------- 20 Composite video input
Ground (0V) 6 -+---------+- 13 Red ground
Ground (0V) 7 -+ +- 9 Green ground
Ground (0V) 8 -+ +- 5 Blue ground
Ground (0V) 9 -+ +- 13 CVBS video ground

Ideally each ground wire should be linked to a separate Arc pin. Also, depending on your SCART monitor, pin 16 may need a +5V input to it. Unfortunately the Arc 9 pin socket does not provide a +5V output so this will have to be sourced from somewhere else.

If you have a newer Acorn machine, with the 15 pin high density video socket then you need this kind of wiring :-

.--------------------. 15-pin VGA style plug
\ 1 2 3 4 5 /
\ 6 7 8 9 10 /
\ 11 12 13 14 15 /
'--------------'

Connections:

Arc SCART

1 red ---------------------------- 15
2 green--------------------------- 11
3 blue---------------------------- 7
4 ID[2] nc
5 0V (test)
6 red rtn------------------------- 13
7 green rtn----------------------- 9
8 blue rtn------------------------ 5
75 ohms
9 +5V-------------/\/\/\/--------- 16
10 0V----------------------------- 17,18
12 ID[1]-------------------------- 8
11 ID[0] <--13 |
13 HSync -->11 |
120 ohms
14 CSync------------/\/\/\/------- 20
15 ID[3] nc

Notice the two resistors. Also notice that the HSync output (pin 13) of the 15-way plug has to be connected to the ID[0] input (pin 11) of the same plug. (Be aware I have no direct confirmation that this wiring works.)

As is usual care must be taken when doing this procedure. Older Acorn machine did not have their VIDC chips fully buffered and unplugging/plugging cables from the video socket while the machine is turned on can cause damage to the video circuitry.

If you want to connect a BBC B computer to a Scart monitor, there are some online wiring diagrams at www.astro.livjm.ac.uk/~bbc/monitor/monitor.html

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Q2.9) How do I make a Null modem cable?

For starters you will need soldering skills and the necessary components.
Namely cable, connectors (9 pin female D-type), a soldering iron, solder and the will to use them. All of these items, bar the will, can be found down at the local electronic components store. Assuming you have them all then you will need to decide what kind of machines you are hooking together.

There are three cases and I need to define a few terms.

'Archimedes' is defined to be A300 series, A400 series (including the /I machines), R140, A540, A3000 (but not the A30x0 machines) and R260 machines.
'RiscPC' is defined to be both the RiscPC series but also the A5000, A4000, A30x0 & A4 machines. All of these machines have a 'PC Style' serial port that conforms closely to RS232 specifications.

This means that if you are connecting your Acorn machine to a non Acorn machine then generally treating the foreign machine as a RiscPC, in terms of serial handling, will work. There are exceptions, Macintoshes in particular have had non-standard serial ports and may require further research before you can create a cable for them.

The cases are :-

Archimedes to Archimedes

Arc (9 pin) Arc (9 pin)
----------- -----------

Archimedes to RiscPC

Arc (9 pin) RiscPC (9 pin)
----------- --------------

RiscPC to RiscPC

RiscPC (9 pin) RiscPC (9 pin)
-------------- --------------

2---RxD------------------------TxD----3

3---TxD------------------------RxD----2

4---DTR---------------------+--DSR----6
|
6---DSR--+ +--RI-----9
| |
9---RI---+ +--DCD----1
|
1---DCD--+---------------------DTR----4

5---0v-------------------------0v-----5

8---CTS------------------------RTS----7

7---RTS------------------------CTS----8

Note that most PC compatible machines have 25 pin D type male ports for their second COM port. You have two options in this case - either re-wire the cable for the 25 pin port or you can buy a 9 to 25 pin converter plug.
Either solution works well. Here are the relevant pins for the 25 pin port :-

Pin No. Function
------- --------
8 DCD
3 RX
2 TX
20 DTR
7 GND (0v)
4 RTS
5 CTS

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Q2.10) What are StrongARM dipswitch settings?

The StrongARM card has a set of dipswitches on it that control the clock speed of the processor.

These can be altered but there are some important caveats to mention first :-

This information is for the original 202MHz StrongARM. The newer 233MHz ones can't be clocked as high, as the base crystal speed is different.

Don't change the links while the card has power. This can result in damage to your processor, always turn your machine off before changing settings.

By default two tracks on the back of the card constrain the card to never go faster than 202 MHz. Cutting these tracks invalidates your warranty, so only do this if you are prepared to replace the card.

The chip is officially rated for 202 MHz, running it faster than this speed can result in hardware damage to the processor and will shorten the chip's lifespan. Again, only do this if you are prepared to replace the card.

If you do cut the tracks remember that the card is a multi-layer one, cutting deeper may sever more tracks than you intended and render the card non-functional.

Without cutting the tracks, the dip switches can be used to slow the processor down from 202MHz to 88MHz if required. Each switch sets one bit making sixteen possible speed settings. This table summarises those speed settings :-

Switches | SA frequency
----+----+----+----+------------------+---------------------
1 | 2 | 3 | 4 | Revision J and K | Revision R, S and T
----+----+----+----+------------------+---------------------
on | on | on | on | 88.473600 MHz | 85.909080 MHz
on | on | on | off| 95.846400 MHz | 93.068170 MHz
on | on | off| on | 99.532800 MHz | 96.647715 MHz
on | on | off| off| 106.905600 MHz | 103.806805 MHz
on | off| on | on | 143.769600 MHz | 139.602255 MHz
on | off| on | off| 151.142400 MHz | 146.761345 MHz
on | off| off| on | 162.201600 MHz | 157.499980 MHz
on | off| off| off| 169.574400 MHz | 164.659070 MHz
off| on | on | on | 191.692800 MHz | 186.136340 MHz
off| on | on | off| * 202.752000 MHz | 196.874975 MHz
off| on | off| on | 213.811200 MHz | 207.613610 MHz
off| on | off| off| 228.556800 MHz | 221.931790 MHz
off| off| on | on | 243.302400 MHz | * 236.249970 MHz
off| off| on | off| 258.048000 MHz | 250.568150 MHz
off| off| off| on | 276.480000 MHz | 268.465875 MHz
off| off| off| off| 287.539200 MHz | 279.204510 MHz

The default speeds are indicated with *'s.
(Thanks go to Matthias Seifert for this information.)

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Q2.11) Are there any PIC programmers available for RISC OS?

Robert Sprowson has produced an application called !PICsuite which caters for PIC programming under RISC OS. There is also a free PIC assembler to download, which has BBC Basic style assembly conventions. Visit http://www.sprow.co.uk/pics/ for more information.

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Section 3: Configuration

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Q3.1) What is ADFSBuffers and what is the best setting for it?

ADFSBuffers are Read Ahead and Write Behind buffers for ADFS on your Archimedes. These are designed to improve the speed of filing operations by doing work at optimum times. There are some side effects of using them though. When active under RISC OS v2.00 and v2.01 discs must be dismounted before being removed from the floppy drive. Failure to do so results in the dreaded 'FileCore in use.' error. However if you are prepared to sacrifice the speed improvement they give configuring the buffers to 0 does rem
ove this problem. (Or so I am informed.)

Under RISC OS v3.00, as supplied with the early A5000 machines, these buffers generate a different problem and must always be configured off. Failure to do so results in spurious errors when using the Hard Drive on an early A5000. Symptoms include reformatting of crucial sectors of the disc, disc address errors and general failure to save files to the drive. So when using an A5000 with RISC OS 3.00 remember to configure them off!

With RISC OS v3.10 all of the old problems have been cured with a new one introduced. Namely that if you have only a few ADFSBuffers configured and are accessing the floppy drive then your machine can occasionally lock up completely for you. It appears that any value of ADFSBuffers above 8 causes that problem to be largely alleviated (read it only occurs rarely at these settings). So under RISC OS 3.10 it is recommended that you set your ADFSBuffers to 8+. There is a patch module available, called ADFSUtil
s, that does fix this problem - contact your local dealer for a copy of it.

By default RISC OS 3.5 seems to have all of these problems cured and no new bugs introduced.

Under 3.5 the number of ADFSBuffers can be left at the OS's discretion and generally the OS chooses a number based on the amount of memory present in your RiscPC. Unfortunately this cannot be said of RISC OS 3.6, 3.7 or 3.5 using a softloaded copy of the 'extended' FileCore. When running under these conditions if you have a hard drive partition larger than 2 GB then the buffers must be configured off to allow the drive to work, however installing ROM Patch 3 from the Acorn ftp site will fix this bug with l
arge hard discs.

As for the optimum settings for ADFSBuffers, from some speed tests conducted on an A5000, then it has been observed that configuring the maximum of 255 buffers increases drive access speeds by 40-50% (this varies considerably with the type and make of drive) over accesses with no buffers at all. However it achieves only a 15-20% gain over using 32 buffers.

All in all ADFSBuffers behave in a fashion standard for caches. Enlarging the cache size does produce increasing gains, but there are increasingly limited gains as the cache size enlarges. So 255 buffers is better than 128 buffers but not twice as good. However at the low end there does seem to be a degree of synergy between the caches and the drive that means that 64 buffers is twice as good as 32 buffers. Accordingly I recommend that people use at least 64 buffers, more if they can spare the RAM.

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Q3.2) How do I enable solid drags in RISC OS 3?

Solid drags are controlled by bit 1 in byte 28 of the CMOS RAM. Setting this bit enables solid drags on all solid drag 'aware' applications. However setting this bit using a *FX command from the command line is a foolish way to do it, as this will unset/set the other 7 bits in that byte which have meaning to FileSwitch and the Wimp. Accordingly the recommended way to set this bit is using a program like this BASIC one enclosed below :-

REM Toggle state of DragASprite bit in CMOS
REM Read byte
SYS "OS_Byte",161,&1C TO ,,byte%
REM EOR byte with mask for bit 1
byte% = byte% EOR %10
REM Write byte back again
SYS "OS_Byte",162,&1C,byte%
END

Which safely sets bit 1 while preserving the settings of the other bits.

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Q3.3) To what size should I partition my Hard Drive?

This is a complicated question to answer with any hard and fast rules.
For starters the media and filing system being used must be considered. If you are using an IDE drive under ADFS then you usually should have your drive formatted as one whole partition due to ADFS' inability to support multiple partitions. (Although third party extensions, like Alsystems PowerIDE software, can extend the default IDE interface to include partioning.) However this is not always true and sometimes it can be beneficial to sacrifice a few Mbs of partition size to gain tens of Mb savings in red
uced space wastage when storing files.

RISC OS uses, and through FileCore virtually all filing systems share this, a fairly complicated map system that tries to make a reasonable compromise between filing system overheads, speed and flexibility. For drives 512Mb or less this system works quite well. With the advent of easily available multiple Gb size drives the system begins to suffer a little.

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