The Z88 has 32K of internal RAM. This is not enough memory for every day use.
The memory can be increased two different ways.
- Externally - by changing the RAM chip in an external card.
- Internally - by changing the 32K RAM chip
Choosing a memory chip that works with the Z88 is important. Manufactures and the availability of chips change. See Memory Chips for the most 'up-to-date' results.
RAM chips
There are 3 types of RAM chips
- Static RAM
- Pseudo Static RAM
- RAM that should work but doesn't
Modern Static RAM chips are top of the list. They are now manufactured in smaller packages rather than the DIL packages that are used on the Z88 Motherboard and some external cards. unbelievable low current consumption when compared to the RAM chips used in the 1980's give longer battery life. Fortunately, PCB Footprint Converter are available. This allows these smaller size chips to be used now with the Z88.
Pseudo Static RAM chips were used in the 1980s as true static RAM was expensive. From the outside they appear to be like static RAM but internally they have a clock chip that need to refresh the memory before it forgets the value. This overhead means that the chips will need more power than true static RAM.
There are some RAM chips that according to the application or data sheets should work, but don't. They are only found by trying them and the reason why they don't work will remain unknown.
PCB Footprint Converters
To aid construction, these converters may be used to allow the new surface mount devices to be used as larger devices. Let's face it, DIL or DIP packages are a lot easier to handle and solder. These converters may be used to 'bridge that gap.' Here are some examples:-
 | 32 pin SOIC to DIL PCB |
 | 44 pin tsop to DIL PCB |
External RAM (fitted in the card slot)
The maximum size of RAM that can be fitted is 1M byte.
These became available about a year after the Z88 was released, but at £200 each, most users bought the 128K at just under £50.
Memory prices have fallen since then so this is more attractive now.
1M RAM
 | Amplia un cartucho de Z88 hasta 512Kbytes - Convert 32K RAM card to 512K RAM The memory chip described in the article above is no longer available. Suitable replacements are listed below.. |
  | CYPRESS SEMICONDUCTOR - CY62158ELL-45ZSXI - SRAM, 8MBIT, PARALLEL, 45NS, 44TSOP This memory chip is being used in the Rakewell's Flash/RAM card successfully. TESTED OK |
 | ALLIANCE MEMORY - AS6C8008-55ZIN - SRAM, 8MB, 2.7-5.5V, 1024KX8, TSOP44 TESTED FAILS |
| LYONTEK - LY62W10248ML-55LLI - SRAM, 8M, 1MX8, 2.7-5.5V, 44TSOPII This memory chip is a 'drop-in' replacement for the BSI chip (see below). TESTED FAILS when loading a file in PipeDream. |
| BSI (BRILLIANCE SEMICONDUCTOR) - BS62LV8001EIP55 - IC, SRAM 8M, 1024KX8, 2.4-5.5V, SMD This memory chip has been used in the Rakewell's Flash/RAM card successfully. TESTED OK This part is no longer manufactured. |
512K RAM
| Amplia un cartucho de Z88 hasta 512Kbytes - Convert 32K RAM card to 512K RAM The memory chip described in the article above is no longer available. Suitable replacements are listed below. |
 | ALLIANCE MEMORY - AS6C4008-55SIN - SRAM, 4MB, 2.7V-5.5V, 512KX8, SOP32 Note: This has not been tested. |
Internal RAM
The internal 32K of RAM is not large enough. Upgrading this to 128K or 512K internally is possible, but the original 'built-in' OZ operating system did not use this correctly.
Cambridge Computer commissioned OZ 4.0 ROM and were planning to use this with the new User Guide v3 but only the User Guide was changed. The new ROM was made available to users through the Z88 User Group.
The OZ version 4 ROM was the starting point for the disassembly of the code for subsequent versions of OZ. These are available in internal and external versions.
Z88 Motherboard
Here are where all the main parts are on the motherboard.
The external connector on the RH side was never used.
Note: On this motherboard the RAM socket is a 24 pin which is big enough for 32K. Later versions had a 28 pin fitted.
512K RAM
 | |
  | HITACHI HM658512LP-12 4Mb PSRAM HM658512 (250mW active) TESTED OK by Benny |
| To be written up | Look at the power dissipation Operating Standby CY62148G 20mA 3.5uA HM658512 75mA 2mA
http://www.cypress.com/file/42811/download SOIC to DIL PCB http://www.proto-advantage.com/store/product_info.php?products_id=3100173
|
| ALLIANCE MEMORY - AS6C4008-55PCN - SRAM, 4MB, 2.7V-5.5V, 512KX8, PDIP32 This has not been tested yet |
| |
| ALLIANCE MEMORY - AS6C4008-55SIN - SRAM, 4MB, 2.7V-5.5V, 512KX8, SOP32 This has not been tested yet
|
128K RAM
| ALLIANCE MEMORY - AS6C1008-55PCN - SRAM, 1MB, 2.7V-5.5V, 128KX8, PDIP32 This has not been tested yet |