NeXT Memory improvment possible? Higher capcity?

Started by Rob Blessin Black Hole, January 19, 2018, 09:47:20 pm

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Rob Blessin Black Hole

Hello NeXT Community: I saw this FAQ and the very last paragraph has my wheels turning...

[John Graves, Hardware Engineering, NeXT Computer, Inc. adds]
"The memory system has programmable memory timing such that the number
of processor clocks needed to access a given amount of data can be
tailored to the speed of the memory installed. 70 ns memory is just
enough faster than 80 ns memory to allow the cpu to access the data with
fewer clock cycles. This improves memory system performance.

"70 ns" memory is faster than "80 ns" memory in many parameters other
than just RAS access time. The faster CAS access time in particular
allows the memory system to respond quicker to burst (16 bytes) bus
transfers.

>>>>>> I'm thinking it may be   possible in programming given the engineers statement  to write some whammy to support higher capacity ram chips   , for example the NeXT dimension supports 8Mb simms even though NeXT only officially supported 4 mb simms and in an official NeXTstation brochure
boom here http://www.nextcomputers.org/NeXTfiles/Docs/Hardware/nextstation.pdf  Supports 8, 16 and 32 MB SIMMs in two-SIMM increments.
When denser chips (16 MB) become available, NeXTstations can be
upgraded up to 128 MB

An aha moment , can we prove or test drive this theory  in previous?

What type of denser 16Mb 30 pin chips do we need ,  does that mean a cube in theory would work with 256Mb of ram?

And a Turbo boards or Dimension boards would possible support  64 or even 128Mb 72 pin chips lol  with programming tweaks , would the bottle neck then be the bus speed and processor ?  

Wound shit go up in a puff of smoke lol?

Also it seems like the most underused chip is that DSP 56001 .... any thoughts ?  

Peace Rob


Subject: N1. What type of memory may be installed in a NeXT?

References: NeXTanswers' hardware.620, 92_spring_bulletin
"Announcing NeXTstation Turbo and NeXTcube Turbo"  


NeXT Computer (68030-25MHz/68040-25MHz),
NeXTcube (68040-25MHz):

Number SIMM slots: 16
SIMM group size: 4
SIMM type: 30-pin low profile
SIMM access rating: 100 ns
SIMM capacity: 1, 4 MB (1x8/1x9, 4x8/4x9)
Maximum RAM: 64 MB

The low-profile vertically mounted 4 MB SIMMs are easier to install in
the NeXTcube than the horizontally mounted 4 MB SIMMs because of the
small height clearance above the SIMM slots.  It is possible to install
the horizontally  mounted 4 MB SIMMs, but you will be required to slide
the CPU board and the center tower in simultaneously.

Parity (9-bit) SIMMs can be used in both 68030 and 68040 NeXT machines,
but should not be mixed with non-parity SIMMs. Only 68040 boards with
ROM levels of 2.2 (v63) and higher can use the parity memory to detect
parity errors.    

[One user adds the following unverified claims:]

It is OK to mix parity and non-parity memory, but the system will not
boot unattended. Cubes with early boot ROMs will not work with 4 Mb
parity ram, unless at least 3 banks are used.  The system gives an
exception error on power up. The fix is to get a new boot rom from Next.
You can pay $30, or you may be able to squawk and get one for free.  I
have found Next to be pretty responsive, once I find the right person.

[Jimmie Quan, NeXT Hardware Service, adds:]

The correct version is v66 which was the last or final rev for this series
of 040 boards. This version also fixed the problem in the second paragraph.


NeXTdimension boards (i860):

Number SIMM slots: 8
SIMM group size: 4
SIMM type: 72-pin
SIMM access rating: 80 ns
SIMM capacity: 1, 4, 8 MB (256Kx32, 1Mx32, 2Mx32)
Maximum RAM: 64 MB (32 MB official NeXT)

NeXT didn't officially bless the use of 8 MB SIMMs, but they seem to
fit and work.


NeXTstations (68040-25MHz) serial numbers below ABB 002 6300:

Number SIMM slots: 8
SIMM group size: 4
SIMM type: 30-pin
SIMM access rating: 100 ns
SIMM capacity: 1, 4 MB (1x8/1x9, 4x8/4x9)
Maximum RAM: 32 MB

Faster SIMMS (70/80 ns) don't make the memory system work any
faster than the 100 ns units.


NeXTstation Color (68040-25MHz):  

Number SIMM slots: 8
SIMM group size: 2
SIMM type: 72-pin
SIMM access rating: 80 ns
SIMM capacity: 1, 4 MB (256Kx32/256Kx36, 1Mx32/1Mx36)
Maximum RAM: 32 MB


NeXTcube Turbo (68040-33MHz),
NeXTstation Turbo (68040-33MHz),
NeXTstation Color Turbo (68040-33MHz),
NeXTstations (68040-25MHz) serial numbers above ABB 002 6300:

Number SIMM slots: 4
SIMM group size: 2
SIMM type: 72-pin
SIMM access rating: 70/100 ns
SIMM capacity: 1, 4 ,8, 16, 32 MB (256Kx32/256Kx36, 1Mx32/1Mx36)
Maximum RAM: 128 MB

For maximum performance use 70 ns SIMMs: SIMMs rated at 80 or 100 ns will
be detected upon powerup and the memory system clock slowed to 100 ns.  

NeXT manufacturing introduced the new 25 MHz NeXTstation CPU board
into  production in late June '92. To verify which SIMM type your machine
uses, check the system's memory configuration. You can do this by using
the ROM monitor©s print memory configuration command m. Start with
your machine powered down. Press the Power key to power on. As soon as the
message ªTesting system...º disappears, press
command-command-tilde (~ on the numeric keyboard). Under these
circumstances, this will access the ROM monitor. In the ROM monitor,
type m and press return. Turbo-designed boardsÐincluding new 25 MHz
NeXTstations and all Turbo systemsÐwill return messages reporting
the memory configuration contained in four sockets (sockets 0 -3); old
25 MHz boards will return messages for more than four sockets (usually
8).   You can tell a Turbo-designed board, and the accompanying 72 pin, 70
nanosecond SIMMs, by the fact it only reports information for only four
sockets.  

[John Graves, Hardware Engineering, NeXT Computer, Inc. adds]

The memory system has programmable memory timing such that the number
of processor clocks needed to access a given amount of data can be
tailored to the speed of the memory installed. 70 ns memory is just
enough faster than 80 ns memory to allow the cpu to access the data with
fewer clock cycles. This improves memory system performance.

"70 ns" memory is faster than "80 ns" memory in many parameters other
than just RAS access time. The faster CAS access time in particular
allows the memory system to respond quicker to burst (16 bytes) bus
transfers.
:shock:
Rob Blessin President computerpowwow ebay  sales@blackholeinc.com http://www.blackholeinc.com
303-741-9998 Serving the NeXT Community  since 2/9/93

barcher174

Hi Rob,

The memory capacity is a hardware limitation of the Next custom ASIC. 64mb is the hard limit for nonturbo and 128mb for the turbo models. What -could- be possible is changing the max ram for the nextstations from 32 to 64. This would be an invasive hardware mod though which would require adding the additional sim banks. It's been on my list to try for fun some day, but not at all practical. I have confirmed the controller to be identical to the cube and even got a MO drive to boot in the past.  

The article you quoted is talking about memory timing. This is controllable from the ROM.

bobo68

With "controllable from the ROM" you mean detected during boot and displayed, right?

barcher174

Quote from: "bobo68"With "controllable from the ROM" you mean detected during boot and displayed, right?


I think the ROM is capable of overriding the memory timing. There are no user settings, but the early ROMs for instance force the timing to 100ns.