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Leaving the Z88 alone and using the external cards have quite unexpected advantages (apart from being a lot easier). The first thing the Z88 does when given a HARD RESET is to go to Slot 1 to see if there is a copy of OZ to run from there. If that happens, the program will not access the internal ROM thus putting in into standby mode.

External RAM (fitted in the card slot)

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	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 (fitted on the Motherboard)

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.

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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

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Motherboard Conversion in Service Manual Z88 32kb to 512kb Memory Upgrade  Original Article by Don Walterman
Image Removed	Wide internally your Z88 to 512Kbytes
Picture	Device	Operating	Standby
	32K RAM Standard in Z88 NEC 42832 32k x 8 Pseudo Static RAM 150 mS Datasheet	1 W 200mA	2.8 mW 560uA
	HITACHI HM658512LP-12 4Mb PSRAM HM658512 (250mW active) TESTED OK by Benny 02 Feb 2016  This part is no longer manufactured.	75mA	2mA
	CYPRESS-SEMICONDUCTOR-CY62148ELL-55SXI-IC-SRAM-4MBIT-512KX8-5V SOIC32 Data Sheet This part is no longer manufactured.	20mA	3.5uA
	ALLIANCE MEMORY - AS6C4008-55PCN - SRAM, 4MB, 2.7V-5.5V, 512KX8, PDIP32 This has not been tested yet Datasheet	30mA	4uA
	ALLIANCE MEMORY - AS6C4008-55SIN - SRAM, 4MB, 2.7V-5.5V, 512KX8, SOP32 This has not been tested yet	30mA	4uA

128K RAM

	Z88 32kb 32K to 128K Upgrade The memory chip described in the article above is no longer available. Suitable replacements are listed below.
Picture	Device	Operating	Standby
	ALLIANCE MEMORY - AS6C1008-55PCN - SRAM, 1MB, 2.7V-5.5V, 128KX8, PDIP32 This has not been tested yet	10mA	1uA

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