Memory Modules for HP-75C

[toml_12953]

Did HP ever sell a memory module for the HP-75C of more than 8K? If so what was the part number? If not, were there third-party module makers? I'd like to maximize the RAM on my 75C.

[Sylvain Cote]

(03-18-2024 05:08 PM)toml_12953 Wrote:  Did HP ever sell a memory module for the HP-75C of more than 8K? If so what was the part number? If not, were there third-party module makers? I'd like to maximize the RAM on my 75C.

Unfortunately the maximum RAM the HP-75C/D can have is 24KB.

Reference: HP-75 Service Manual , HP-75 Memory Organization, pages 2-44 to 2-46

[Dave Frederickson]

The Expansion Pod can add an Electronic Disc up to 64k.

[floppy]

(03-19-2024 03:51 AM)Dave Frederickson Wrote:  Electronic Disc

What part number?

[Dave Frederickson]

(03-19-2024 09:06 AM)floppy Wrote:  

(03-19-2024 03:51 AM)Dave Frederickson Wrote:  Electronic Disc

What part number?

The Expansion Pod is the 82718A. The 64k Electronic Disc is OPT #064. Usually the Expansion Pods are found with a 75 attached, like this one.
https://www.ebay.com/itm/364578500258

[floppy]

(03-19-2024 09:49 AM)Dave Frederickson Wrote:  

(03-19-2024 09:06 AM)floppy Wrote:  What part number?

The Expansion Pod is the 82718A. The 64k Electronic Disc is OPT #064. Usually the Expansion Pods are found with a 75 attached, like this one.
https://www.ebay.com/itm/364578500258

+1
Page 7 of https://literature.hpcalc.org/community/...-rm-en.pdf
..
Electronic Disc
The HP 82718A Option 032 or 064 provides either 32 or 64 kbytes of additional random access memory
(RAM). This additional RAM simulates a mass storage device such as a digital cassette or disc drive.
Unlike a mechanical device, however, you get fast data transfer and rugged, reliable operation.
..

[Sylvain Cote]

To my knowledge, there are Expansion Pods versions:

• Listed Expansion Pods
  • 32KB RAM disk with modem (OPT 32) [I have several]
  • 64KB RAM disk with modem (OPT 64) [I have several]
    
• Unlisted Expansion Pods
  • 24KB RAM disk with modem [I have seen one]
  • 24KB RAM disk without modem
  • 32KB RAM disk without modem
  • 64KB RAM disk without modem [I have one]
    

[rprosperi]

(03-19-2024 11:05 AM)Sylvain Cote Wrote:  To my knowledge, there are Expansion Pods versions:

• Listed Expansion Pods
  • 32KB RAM disk with modem (OPT 32) [I have several]
  • 64KB RAM disk with modem (OPT 64) [I have several]
    
• Unlisted Expansion Pods
  • 24KB RAM disk with modem [I have seen one]
  • 24KB RAM disk without modem
  • 32KB RAM disk without modem
  • 64KB RAM disk without modem [I have one]
    

I'm not sure what you mean by unlisted; if not mistaken, I believe the pods without modem were never sold to consumers, these were only sold to large corporate of VAR customers to form the core of some mobile solution, e.g. for surveying, logging, warehouse management, etc. which often also required a wand. Perhaps they were given a new model number, but possibly not.

Does the one you (@Sylvain) have w/o modem have a new or standard p/n ?

[J-F Garnier]

(03-19-2024 11:05 AM)Sylvain Cote Wrote:  [*]Unlisted Expansion Pods

• 24KB RAM disk with modem [I have seen one]
• 24KB RAM disk without modem
• 32KB RAM disk without modem
• 64KB RAM disk without modem [I have one]
  

I have a 64KB unit without modem too, because I removed the modem board :-)
This saves some weight, the line coupling transformer is bulky.

The 24K units are surprising, why bothering to make a different version to save only 8k?
Maybe the initial plan was to have 24k and 64k versions.

J-F

[Sylvain Cote]

(03-19-2024 12:40 PM)J-F Garnier Wrote:  I have a 64KB unit without modem too, because I removed the modem board :-)

Expansion Pod without modem from factory.

(03-19-2024 12:40 PM)J-F Garnier Wrote:  The 24K units are surprising, why bothering to make a different version to save only 8k?

My guest would be, custom units ordered by corporations, probably to save cost.

[Sylvain Cote]

(03-19-2024 11:57 AM)rprosperi Wrote:  I'm not sure what you mean by unlisted;

Not listed in any official price lists. Special units ordered by corporations, my unit was made for AT&T.

(03-19-2024 11:57 AM)rprosperi Wrote:  Does the one you (@Sylvain) have w/o modem have a new or standard p/n ?

My unit does not have any part number on it.

[rprosperi]

(03-19-2024 01:17 PM)Sylvain Cote Wrote:  

(03-19-2024 11:57 AM)rprosperi Wrote:  I'm not sure what you mean by unlisted;

Not listed in any official price lists. Special units ordered by corporations, my unit was made for AT&T.

Interesting! One would think anything AT&T custom ordered in the 80's would include a modem... I have at 2 (3?) AT&T branded pods and have just assumed they included modems, but will have to check, now that you've raised my curiosity. Thanks!

Another variation, I presume from the factory, is the presence of an external speaker. Seems pretty awkward for a unit intended to be mobile, but these were early days of mobile computing...

[Sylvain Cote]

(03-19-2024 02:10 PM)rprosperi Wrote:  .. and have just assumed they included modems, but will have to check, now that you've raised my curiosity. Thanks!

(03-19-2024 02:10 PM)rprosperi Wrote:  Another variation, I presume from the factory, is the presence of an external speaker. Seems pretty awkward for a unit intended to be mobile, but these were early days of mobile computing...

To be more precise, the presence of an external speaker "plug", in which you could insert a wired single mono ear bud.

[toml_12953]

(03-18-2024 07:29 PM)Sylvain Cote Wrote:  

(03-18-2024 05:08 PM)toml_12953 Wrote:  Did HP ever sell a memory module for the HP-75C of more than 8K? If so what was the part number? If not, were there third-party module makers? I'd like to maximize the RAM on my 75C.

Unfortunately the maximum RAM the HP-75C/D can have is 24KB.

Reference: HP-75 Service Manual , HP-75 Memory Organization, pages 2-44 to 2-46

I guess I'll have to buy an HP-71B then. Thanks for the reply!

[KeithB]

Other than the keyboard and real space "bar", is there any other reason to choose an HP-75 over an HP-71?

[Valentin Albillo]

(03-20-2024 03:40 PM)KeithB Wrote:  Other than the keyboard and real space "bar", is there any other reason to choose an HP-75 over an HP-71?

Not really. Speed could be a factor but see this post & my reply.

V.

[Sylvain Cote]

(03-20-2024 03:40 PM)KeithB Wrote:  Other than the keyboard and real space "bar", is there any other reason to choose an HP-75 over an HP-71?

The design spirit of the two machines is different and it shows in a lot of places.

The HP-75C/D is a portable version of a HP 80 series desktop machines.
It use the CMOS version of the 8-bit CPU, same system architecture and has almost the same BASIC implementation.
To me, the HP-75C/D feels like a desktop computer with mobile capabilities.
IMHO, a minimal HP-75 system must have at least: HP-75C/D, 24KB RAM (16KB + 8KB), I/O ROM and Math ROM.

The HP-71B is a generational evolution of the HP-41. → Ever heard of an HP 44A (71B look-alike)
It use a new 4-bit CPU inspired by the 1-bit CPU of the HP-41, a new system architecture and a new BASIC implementation based on Minimal BASIC.
To me, the HP-71B feels like a handheld computer/calculator hybrid with great expandability.
IMHO, a minimal HP-71B system must have at least: HP-71B, 48KB+ RAM (17.5K + RAM modules), HP-IL and Math ROM.

Minimal BASIC → Wikipedia , ECMA-55 , ANSI X3.60-1978
Standard/Full BASIC → Wikipedia , ECMA-116 , ANSI X3.113-1987

A desktop like setup with the HP-75C, VisiCalc ROM, IL/Video interface and a monitor.

[Steve Simpkin]

(03-20-2024 05:22 PM)Sylvain Cote Wrote:  ...
The design spirit of the two machines is different and it shows in a lot of places.
...
The HP-71B is a generational evolution of the HP-41. → Ever heard of an HP 44A (71B look-alike)
It use a new 4-bit CPU inspired by the 1-bit CPU of the HP-41, a new system architecture and a new BASIC implementation based on Minimal BASIC.
To me, the HP-71B feels like a handheld computer/calculator hybrid with great expandability.
IMHO, a minimal HP-71B system must have at least: HP-71B, 48KB+ RAM (17.5K + RAM modules), HP-IL and Math ROM.
...

I had not seen that post and did not realize that the HP-71B started out as a follow-on or replacement for the HP-41 series before evolving into a handheld BASIC computer.

(12-26-2015 10:38 AM)Massimo Gnerucci Wrote:  From "A Guide to Hp Handheld Calculators and Computers" by Wlodek Mier-Jedrzejowicz 3rd edition 1999 p.80

Quote:The Titan was first given the model number HP-44 and was partly a follow-on to the HP-41 and partly an expanded HP-15C. As the project progressed, the calculator features of the HP-44 were subsumed into a handheld computer with a built-in calculator. Titan became a series 70 model, and was given the model number HP-71B, with the 1 derived from the HP-41. The B stood for "Basic-language computer", to distinguish the HP-71B more clearly from the HP-75C and the HP-75D.

I wonder if HP came to a similar conclusion as TI did when cancelling the TI-88 project, that keystroke programmable calculators were a declining market and would largely be replaced by handheld computers programmable in BASIC, FORTRAN and even Pascal.
https://www.hpmuseum.org/forum/thread-16...#pid144813
TI-88 Part 1: History and Go / No Go Decision (Gene Wright)